Category 6™

California Rainy Season Ending; January-April rain in San Francisco Lowest on Record

By: Jeff Masters , 2:44 PM GMT on April 30, 2015

The fourth consecutive severely dry California rainy season is drawing to a close. Rain-bearing low pressure systems typically stop bringing heavy rains to the state by mid-April, as the jet stream shifts to the north in its usual springtime migration. With almost no rain in the forecast for the next seven days, and the 16-day GFS model forecast showing mostly light rains affecting the northern portion of the state 8 - 16 days from now, California has likely seen over 95% of the precipitation that it’s going to get this anemic rainy season. What little precipitation did fall this winter came mainly in the form of rain, thanks to record-warm ocean temperatures off of the coast. This resulted in snow falling only at very high elevations, keeping the critical Sierra snowpack--which provides one-third of the state's water--at record low levels. According to the California Department of Water Resources, snow depths in the Sierras are the lowest on record for this time of year, only 2% of average, and the Southern Sierras have no snow at all--nearly three months earlier than usual. California's eight largest reservoirs are 30% - 83% below their historical average, and the portion of the state covered by the highest level of drought--"Exceptional"--was at 47% this week. The area covered by "Exceptional" drought peaked at a record 58% during the summer of 2014, and this mark may well fall during the summer of 2015.

Figure 1. Aerial view showing recreational boats by the Bidwell Marina at Lake Oroville, California on March 2, 2015. Lake Oroville, California's 2nd largest reservoir, was at 62% of average on April 29, 2015, which was its third lowest level since 1989. Image credit: California Department of Water Resources.

Record dryness in San Francisco
According to wunderground weather historian Christopher C. Burt, with just 1.30” of precipitation in downtown San Francisco this April and no chance of any additional rain to the end of the month, the January-April period will have a total of only 2.89”--easily the lowest on record, and well below the approximately 11.5" of rain the city usually gets. San Francisco got no rain at all in January, the first January on record that has occurred. Here is a list of the top ten driest Jan-April periods on record since 1850 in San Francisco:

1.   2.89” 2015
2.   3.54” 2013
3.   3.68” 1898
4.   4.01” 1976
5.   4.43” 1851
6.   4.75” 1972
7.   4.92” 1862
8.   4.92” 1864
9.   5.08” 1984
10. 5.11” 1977

Figure 2. Predicted precipitation for the 7-day period ending on Thursday, May 7, 2015. With the exception of light rains in the Sierras, California will be dry this week. Image credit: NOAA/HPC.

The long-range forecast: hot, dry, and more intense drought
The latest 3-month outlooks from NOAA's Climate Prediction Center, private forecasting firm WSI, and Columbia University's International Research Institute for Climate and Society all call for above-average chances of hotter than usual weather in California though July, and the U.S. Seasonal Drought Outlook calls for drought to persist or intensify over California. This should be no surprise, given that ocean temperatures along the coast of California are at record or near-record levels for this time of year, and will be slow to change. These record warm ocean temperatures will drive hotter weather and more intense drought this summer than otherwise would occur, and this summer's fire season will likely be severe. Next winter, California has a decent chance of getting a better rainy season, if the current El Niño event manages to intensify into a strong one (an event predicted by several of our better El Niño models.) Still, the Sierras need 1.7 - 2.9 times more precipitation than a usual rainy season brings to bust the drought; some portions of the state need even more than that.

Figure 3. Ocean temperatures off the coast of California were at record or near-record levels for this time of year on April 29, 2015. Ocean temperatures off the coast of Los Angeles and San Diego were more than 4°C (7.2°F) above average, an astonishingly high anomaly. These high temperatures were due to a combination of effects: a very persistent ridge (the Ridiculously Resilient Ridge, or RRR) that has been in place along the West Coast much of the past three years, bringing warm air temperatures and little mixing of cool waters from the depths; a positive phase of the Pacific Decadal Oscillation (PDO), a decades-long natural pattern; and global warming, which has warmed oceans world-wide over the past century-plus. Image credit: NOAA Environmental Modeling Center.

Portlight disaster relief charity raising funds for Nepal earthquake relief
The disaster relief charity, founded and staffed by members of the wunderground community, has connected with disability stakeholders in Nepal, India and Pakistan to seek their input on how best to help our brothers and sisters affected by their devastating earthquake. Portlight has determined that they can be of the most service by raising funds to directly support the relief and recovery efforts of these and other in-country stakeholder organizations. You can donate to this effort at this link:

You can follow the progress of the relief effort on the Portlight Blog. Thanks!

FYI, we are having some technical issues with some of the blog comments disappearing, and are looking into the cause.

Jeff Masters


Air Pollution and Dust Credited With Weakening Hurricanes Irene and Katrina

By: Jeff Masters , 1:30 PM GMT on April 28, 2015

As Hurricane Irene churned northwards out of the Bahamas towards the Northeast U.S. on August 25, 2011, residents there scrambled to prepare for the arrival of what could well be the most destructive hurricane ever to hit the United States. Irene had just devastated the northern Bahamas as a Category 3 storm with 120 mph winds, and the National Hurricane Center forecast called for the hurricane remain at Category 3 strength as it plowed over the Outer Banks of North Carolina. Irene was then expected to slowly weaken to Category 1 strength at landfall on the New York/New Jersey coast three days later. Fortunately, Irene surprised forecasters by weakening unexpectedly to a Category 1 storm at landfall in North Carolina, and further weakening to a strong tropical storm with 70 mph winds when it reached New York City on August 28. Even so, Irene did $16 billion in damage, making it the 7th costliest U.S. hurricane in history, and most expensive hurricane ever to hit the Northeast U.S. (until Hurricane Sandy in 2012.)

Figure 1. Tropical Storm Irene, with top winds of 70 mph, was centered almost directly over New York City in this image taken on August 28, 2011.

Figure 2. The European (ECMWF) model is not known for making good intensity forecasts, and is not one of the intensity models the National Hurricane Center uses to make intensity forecasts. Nevertheless, its 4-day forecast of Hurricane Irene making landfall in Delaware as a borderline Category 3/Category 4 hurricane with a central pressure of 936 mb had forecasters like me sweating a bit.

Why did Irene weaken?
Like most intense hurricanes, Irene underwent an eyewall replacement cycle, a process where the inner eyewall shrinks, becomes unstable, and collapses, and is replaced by a new outer eyewall that forms from an outer spiral band. Typically, this process results in a temporary weakening of the storm of 10 - 30 mph in peak winds and 10 - 20 mb in pressure. After about a day, though, the outer eyewall usually grows more organized and contracts, and the storm re-intensifies. Unexpectedly, Irene never completed its eyewall replacement cycle after it left the Bahamas, and the size of the new outer eyewall grew in parallel with an intensification of the hurricane’s outer rain bands. This resulted in the somewhat unusual case where the minimum pressure occurred 40 hours after the winds peaked in intensity. Research accepted for publication last week in the Journal of Atmospheric Science, led by Barry Lynn of The Hebrew University of Jerusalem, "The sensitivity of Hurricane Irene to aerosols and ocean coupling: simulations with WRF spectral bin microphysics", gives partial credit for Irene’s weakening to dust and air pollution sucked in by the storm. These particles (collectively called aerosols) invigorated the outer spiral bands and outer eyewall, and kept the outer portions of the storm strong at the expense of the inner core. Using a high-resolution model that used a 1-km grid to simulate the storm, the researchers were able to show that dust particles from the Saharan Air Layer (SAL) and air pollution particles from the Eastern U.S. could have caused a weakening of Irene’s winds of 20 - 30 mph, accompanied by an increase of 10 - 15 mb in the central pressure, and caused the observed delay of the storm’s lowest pressure occurring 40 hours after the winds peaked. Unfortunately, none of the hurricane intensity models that NHC uses include aerosol particles, or have the fine 1 km resolution used in the Hurricane Irene study. I hope that within a few years, computers will become powerful enough to run such a model in real time for use in operational forecasting.

How do aerosols weaken a hurricane?
Aerosol particles of the right size and composition (called Cloud Condensation Nuclei, CCN) provide convenient places where water vapor can condense and form cloud droplets. An increase in concentration of small aerosols increases droplet concentration and decreases droplet size. The net effect is a decrease in the collision rate to form large raindrops, and a delay in raindrop formation and rain. As a result, small droplets ascend in cloud updrafts and continue growing by condensation, leading to an increase in supercooled water content. When the moisture condenses in these updrafts, it releases extra "latent heat" (the energy it took to vaporize the water originally, which the water vapor stores). This release of energy leads to an increase in cloud updrafts and an increase in cloud top height and lightning. When this process occurs in the outer bands of a hurricane, the resulting invigoration of the thunderstorms there creates heavy rain that drags down cold air from aloft to the surface, creating pools of cold air near the surface that act to block the inflow of warm, moist air into the hurricane's core, thus weakening the storm.

Figure 3. Dry air/Saharan Air Layer (SAL) maps from the University of Wisconsin - CIMSS ( for 18 UTC 21 August 2011 (top) and 00 UTC 24 August 2011. Hurricane Irene crossed a wide band of Saharan dust during its northward movement. Figure 3 (top) shows that Saharan Air Layer dust impinged on Irene in three sectors at 18 UTC 21 August 2011. Fifty-four hours later (0000 UTC 24 August 2011) most of the dust was not observable by satellite, but it was still seen to Irene's north in a cloud-free area (Figure 3, bottom). This indicates that the dust seen at the earlier time was likely absorbed into Irene’s circulation.

Figure 4. Official NHC intensity forecasts for Irene every 6 hours from 1200 UTC 23 August to 0600 UTC 28 August. The black line is the observed intensity of Irene. NHC consistently over-predicted the strength of Irene's winds.

Aerosols are also credited with weakening Hurricane Katrina
According to Khain et al. (2010), ”Aerosol Effects on Intensity of Landfalling Hurricanes as Seen from Simulations with the WRF Model with Spectral Bin Microphysics”, ingestion of aerosols also may have been responsible for weakening Hurricane Katrina as it approached landfall in Mississippi on August 29, 2005. Katrina peaked as a monster Category 5 storm with a central pressure of 902 mb and 175 mph winds about 24 hours before landfall, but weakened to a Category 3 storm with 125 mph winds and a 923 mb central pressure when it came ashore. Up to 35 mph of the wind decrease and 15 mb of the pressure rise could have been due to the storm pulling in aerosol pollution and dust particles from Southern U.S. in the final 24 hours before landfall, the authors deduced, using a detailed computer model of the storm.

Why not use aerosols to intentionally weaken hurricanes?
Since we’re pretty sure that aerosols can help weaken hurricanes, why not intentionally introduce small particles into a hurricane to control its intensity? That was the rationale behind a $1 million study by the Department of Homeland Security between 2009 - 2011, HURRMIT (The Identification and Testing of Hurricane Mitigation Hypotheses). Scientists with the project conducted a number of computer simulations on what would happen to a hurricane by intentionally spraying small aerosol particles into the storm using aircraft. They found that in theory this approach would work, with winds decreasing 20 - 30% for Category 4 and weaker hurricanes. However, the hurricanes had to be treated during an intensification phase to get these reductions in intensity; the effect was significantly less when the simulated storm had completed an intensification cycle and was fully mature. In addition, they found that putting too much aerosol into a hurricane’s outer rain bands thrust more water substance into the thunderstorm anvils, lowering storm precipitation efficiency and short-circuiting the reduction in surface winds.

It is quite possible that seeding a hurricane with aerosol particles can actually make the storm more intense, though. The authors of the Hurricane Irene study commented that if aerosols can manage to penetrate directly to the core of a hurricane, they can act to invigorate the inner eyewall and make the storm stronger. In addition, putting aerosols into a tropical depression in its formative phase can help it, since the storm typically needs an extra boost in cloud droplets to get going (however, the dry air that often accompanies aerosols from the Saharan Air Layer often destroys a budding tropical depression.) So, we’d better be really sure we know what we’re doing if we are going to be intentionally messing with hurricanes. I am very sure that we are not really sure, and that we should leave hurricanes alone for the foreseeable future!

Related: my 2009 blog post, Bill Gates Takes on Hurricanes.

Jeff Masters

Air and Water Pollution Hurricane

Massive Tornadic Storm Just Misses Dallas; Extreme Heat in South Florida, Cuba

By: Bob Henson , 12:09 PM GMT on April 27, 2015

Near-record atmospheric moisture for late April teamed up with an extremely strong jet stream to produce a fearsome night of severe weather over north Texas, mainly south of the Dallas-Fort Worth area. The most intense storms of the day developed by early afternoon southeast of Abilene, with one large supercell emerging at the south end of the complex. After producing several brief tornadoes and hail as large as softballs from a giant stacked-plate circulation, the storm grew even larger and more threatening after dark as it moved just south of the DFW area. Slowing and reoganizing, it dumped more than 5” of rain on some areas, according to Doppler radar estimates. At one point, there were three potentially tornadic circulations evident on Doppler radar along the storm’s south edge, a pattern eerily reminiscent of the deadly storm on May 30, 2013, that killed several storm chasers near El Reno, Oklahoma. Soon after midnight, the circulations congealed into a powerful comma-shaped bow echo that swept across the prairie with high winds (see Figure 1). Nineteen preliminary tornado reports were logged by NOAA's Storm Prediction Center in Texas on Sunday.

Figure 1. National Weather Service radar imagery from 11:55 pm CDT Sunday, April 26 (left) and 12:55 am CDT Monday, April 27 (right) shows the dramatic evolution of the storm complex south of Fort Worth into a bow echo (right), with a “bookend” circulation evident on its north end. Here's an animation from NCAR showing the storm's evolution on radar. Image credit: Weather Underground Storm.

Sunday night’s storm would have been far more destructive had its track been just one county north, across Fort Worth and Dallas. Just two nights earlier, parts of the Fort Worth area were racked by a powerful downburst that brought winds estimated at 80 – 85 mph. That storm went on to produce high winds all the way to Mississippi, with three brief EF1 tornadoes reported there. Another storm complex produced an even more extensive swath of high wind on Saturday, stretching nearly 500 miles from southeast Louisiana to the Georgia coast. Also on Saturday, hail up to baseball size pounded central Kentucky, with a short-lived EF2 tornado reported northwest of the town of Brownsville.

Figure 2. A hazy sunset on Saturday night, April 26, served as a prelude to Miami’s record heat on Sunday. Upper-air analyses carried out by the National Weather Service traced a smoke layer that lay a few thousand feet above the city on Saturday back to its origin several days earlier above fires on Mexico’s Yucatan Peninsula. Image credit: NWS/Miami.

Heat wave blasts April records in South Florida and Cuba
The spring of 2015, already one of the warmest on record across southeast Florida, turned it up a notch on Sunday, as residents baked in heat that would be unusual even in midsummer. Fort Lauderdale International Airport broke its all-time April heat record with 96°F, while Miami tied its April record with the same reading. Fort Lauderdale Executive Airport sizzled at 99°F; this was just 1° short of the city’s all-time any month record of 100° achieved on Aug. 4, 1944 (records date back to 1912 in the city.) In addition, one preliminary report of 100°F came in from the Boca Raton area. The day’s heat was not only intense but persistent: Miami hit 96°F at 1:27 pm and stayed above 90°F for eight torrid hours. Strong westerly winds kept the typical afternoon cooling from the sea breeze at bay.

Figure 3. The weekly U.S. Drought Monitor issued on April 23 showed an area of severe drought (orange) across far south Florida that had grown fivefold in size from the previous week. Image credit: National Drought Mitigation Center.

The heat may have also gotten a boost from parched ground across far southern Florida, where drought conditions have intensified rapidly in the last several weeks (see Figure 3). Dry ground heats up more readily than moist ground in full-sun conditions, and Sunday’s westerly winds swept across the drought area en route to the big east-coast cities. Miami is coming off its second-warmest March on record, and April is currently running at the warmest pace on record (80.4°F). Even with slightly less brutal temperatures on tap this week, April should end up toppling the monthly record of 80.1°F set in 2011.

The heat has been even more impressive in nearby Cuba, where Havana set its all-time temperature record on Sunday with a sizzling 37.0°C (98.6°F). The day also brought the second-highest temperature ever recorded anywhere in Cuba: 38.7°C (101.6°F), at Holguin. These data were provided courtesy of Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. He notes that these records are all the more impressive since July and August are usually the hottest months in Cuba.

Bob Henson

Tornado Severe Weather Heat

Updated Flagship WU App for All iOS Platforms, including Apple Watch

By: Bob Henson and Jeff Masters , 2:47 PM GMT on April 24, 2015

The latest version of Weather Underground’s flagship app is now available for iPad, iPhone, and iPod touch, as well as Apple Watch, which debuts on Friday. The app is free to download from the App Store, including the dedicated App Store for Apple Watch.

Small is beautiful
WU developers have compressed many of the features familiar to WU fans into an elegantly compact format for Apple Watch, which measures about 1.6” by 1.4” wide. This format includes:

• “Force Touch” navigation for quick access to hourly outlooks, ten-day forecasts, and saved locations, plus options for graph view and list view
• Notifications on the latest NWS severe weather alerts
• Real-time radar and satellite imagery

Users across iOS platforms will find a range of enhancements in the latest version of the WU flagship app, including:
• A new layout for quick access to your favorite weather data
• An “interface-lift” that allows the most customizable app experience yet, including light or dark mode, map types, metric/English units, and rearrangeable tiles
• Worldwide storm tracking on the hurricane and tropical storm tile
• The ability to submit local sky and hazard reports
• New animations and visualizations for health information (UV index, pollen counts, flu prevalence)

“Timing is everything with weather, and we want to ensure that users receive the most accurate, hyper-local weather information possible, which is why we’ve made it easily accessible across all iOS devices,” says Jim Menard, Senior Vice President and General Manager of Weather Underground.

WU is working on some exciting options for Android fans as well. Stay tuned for more details.

Strong tornadoes possible Friday in southern Plains, Saturday in Tennessee Valley
Another round of severe weather is expected to fire up from Kansas to Texas on Friday afternoon, spreading into the Mississippi Valley overnight. This time the tornado threat will be heightened by a strong upper-level wave flowing atop unstable air pooled along a dry line and warm front. Last night’s models slowed down the approach of the upper wave, which should allow for deeper moisture and stronger vertical wind shear to support potentially tornadic supercells along a corridor that includes Dallas/Fort Worth, Oklahoma City, and Wichita. Extensive thunderstorms that covered much of Texas on Friday morning should move off to the east later in the day, permitting at least some heating and destabilization of the air mass. NOAA’s Storm Prediction Center has placed parts of Kansas (near the intersection of the dry line and warm front) and northeast Texas into northwest Louisiana (where moisture should be especially rich) under an enhanced risk of severe weather, with very large hail possible in both areas and significant tornadoes possible in the southern area. We’ll be covering Friday’s severe weather in a live blog accessible from the WU home page.

A significant tornado threat may emerge on Saturday in and near Tennessee and southwest Kentucky as the system moves east; SPC has placed this area under an enhanced risk in its Day 2 outlook. Yet another round of substantial severe weather may unfold on Monday across Texas, with models suggesting that an especially potent upper low will encounter deep moisture and extremely high instability.

Unique climate odyssey to set sail in June
This June, a unique year-long sailing expedition and art and science collaboration called Climate Odyssey will depart from Manitowoc, Wisconsin, go through the Great Lakes, head down the Erie Canal, then make its way southwards along the U.S. East Coast to the Caribbean. Along the way, hydrologist Zion Klos and artist Lucy Holtsnider will be photographing climate change impacts and adaptation strategies, interviewing stakeholders, politicians, scientists and artists, and visiting classrooms and community groups. They will share their photographs and encounters in an interactive digital map and blog on their website. Each image added to the digital map will be linked to relevant blog entries and other adaptation resources, making the map both a piece of art and an engaging tool for sharing the science of climate change. At the end of the journey, they will print out the digital map and make it into an artists' book, like this prototype at right, to be shared in libraries, galleries, and classrooms in those same communities they visited. Jeff had the opportunity to meet this creative duo last summer at a workshop on climate change communication hosted by the American Geophysical Union, and enjoyed experiencing their energy and dedication. Communicating the magnitude of the climate change challenge is one that can use more innovative efforts like theirs, and we encourage you to join us in supporting the Climate Odyssey by contributing to their Indiegogo fundraising campaign, needed to cover the costs of restoring the old sailboat they are using.

Have a good weekend, everyone!

Bob Henson and Jeff Masters

Earth Day Updrafts: Supercell in Texas, Volcano in Chile

By: Bob Henson , 4:43 PM GMT on April 23, 2015

A spectacular supercell thunderstorm over the Texas Panhandle on Wednesday afternoon morphed into a sprawling complex that moved across North Texas overnight with strong winds, heavy rain, and hail. The original supercell dropped several brief tornadoes south and east of Amarillo and displayed some impressive structure (see Figure 1) before it merged with other storms to form a mesoscale convective system (MCS). These large clusters of showers and thunderstorms can persist for more than 12 hours, often forming in the evening and persisting until morning.

Figure 1. This supercell northwest of Floydada, Texas, has the classic corkscrew appearance produced by the rotation of the entire thunderstorm. The supercell produced several brief tornadoes. Image credit: Brock Burghardt.

Wednesday night’s MCS drew from a pool of deep moisture over Texas, and it was hustled along a northwest-to-southeast frontal zone by powerful jet stream winds, exceeding 140 mph above the DFW area at 0000 GMT Thursday. Further south, another complex of storms developed near Corpus Christi earlier in the day, toppling power poles and downing power lines with wind gusts estimated at 70 mph, before moving into the Gulf of Mexico, where it maintained impressive vigor into the night. A buoy about 100 miles south of Houston reported a wind gust to 87 mph. Remnants of this MCS moved across Florida on Thursday morning. The strong upper winds prevalent across the East also worked their way to the surface in and near New Jersey on Wednesday afternoon. A batch of modest rainshowers produced downburst winds that gusted to 71 mph at Philadelphia International Airport around 3:00 p.m.

Figure 2. The Day 2 convective outlook valid on Friday, April 24, shows an enhanced risk of severe weather across parts of the southern Great Plains. Image credit: NOAA/SPC.

More severe weather on the way into next week
Conditions are ripe for more tornadic storms and MCSs over the next several days across the south-central states, as upper-level energy ripples along the strong jet stream and rich moisture remains in place. A slight risk of severe weather is in place for Thursday across parts of central Texas, southern Louisiana, and eastern Colorado/western Kansas. More significant severe weather is expected on Friday, with NOAA’s Storm Prediction Center already highlighting the possibility of strong tornadoes ahead of a dry line that should extend from central Kansas to central Texas. SPC’s Day 2 outlook for Friday shows an enhanced risk of severe weather in two pockets ahead of the dry line (see Figure 2). The ultimate locations of elevated risk will hinge in large part on where storms develop on Thursday night; any widespread activity could leave clouds and rain-cooled air that reduce the amount of instability available on Friday afternoon. The zone of greatest severe risk will shift east across the lower Mississippi Valley and into the Southeast on Saturday.

Another strong upper low could bring renewed severe weather in Texas and Oklahoma by late in the weekend. SPC’s Day 5 outlook is already pointing to a ramped-up probability of severe weather on Monday in central Texas, a rare upgrade for so far into the future. The last several runs of the longer-range GFS model suggest this upper low would continue eastward as a distinct system across the Gulf states early next week, with very strong thunderstorms and heavy rain eventually possible as far southeast as Florida, while the latest run of the ECMWF model (issued at 0000 GMT Thursday) moves the upper-level energy more slowly and in a weaker form. Before the month is done, Kentucky should get one or more bouts of heavy rain, possibly giving several cities their wettest April on record, including Frankfurt (10.68” to date; record 13.95” in 2011); Lexington (10.61” to date; record 12.70” in 2011); and Louisville (10.61” to date; record 13.97” in 2011).

Figure 3. Children in Puerto Varas, Chile, watch the Calbuco volcano erupt on Wednesday, April 22, 2015. The volcano’s huge ash cloud spread over a sparsely populated, mountainous area in southern Chile. Authorities ordered the evacuation of the inhabitants of the nearby town of Ensenada, along with residents of two smaller communities. Image credit: AP Photo/Carlos F. Gutierrez.

Chile’s Calbuco volcano springs to life
For sheer visual power, Wednesday’s U.S. thunderstorms were eclipsed by the surprise eruption of Calbuco in southern Chile, just north of Patagonia. The volcano, located near Puerto Montt in the Los Lagos region, has a peak elevation of about 6,500 feet. Wednesday’s event was Calbuco’s first eruption since 1972 and the first major one since 1961. The initial burst of ash formed a narrow column that quickly reached the stratosphere (at least 10 km high) and spread out into an anvil cloud resembling that of a severe thunderstorm (Figure 3). Overnight, a second eruption was reported, with lava flows and lightning painting a eerie, brilliant scene. This Mashable photo album shows the many faces of the Calbuco eruption as the day and night unfolded. About 4,000 nearby residents had evacuated by late Wednesday, but there were no immediate reports of injury.

Vulcanologist/blogger Erik Klemetti at Wired pointed out that the eruption’s initial phase was “a classic Plinian column”—a term derived from the infamous A.D. 79 eruption of Mount Vesuvius, which was documented by Pliny the Younger. The apparent height and nature of the plume from Calbuco would put the volcano’s first eruption on Wednesday at a ranking of at least 4 (“cataclysmic”) on the Volcanic Explosivity Index, which runs from 0 to 8. It would take a much more potent eruption to generate the massive impacts on climate described by Jeff Masters in his recent post on Indonesia’s Mount Tambora, which produced a colossal eruption 200 years ago.

Erupción volcán Calbuco

Erupción volcán CalbucoGENTILEZA :Felipe Andrés Canales Torres


Video 1. This amazing time-lapse sequence, from Chile’s Centro Información Monitoreo Alerta Temprana, shows the eruption of Calbuco through nightfall Wednesday.

This week’s WunderPoster: Dust devils
If you can appreciate the power of rising air on a more modest scale than a volcanic eruption or a supercell thunderstorm, check out this artistic take on dust devils, the latest installment in our WunderPoster series (Figure 4, right). When the summer sun bakes a field or a desert, a pocket of surface air may heat up enough to create a narrow, rotating updraft. Most dust devils spin harmlessly across the landscape--too small, weak, and short-lived to cause much trouble--but the most powerful can be dangerous, lasting for 10 minutes or more and packing winds exceeding 60 mph. All WunderPosters can be downloaded in formats suitable for posters or postcards.

Bob Henson

Volcano Severe Weather

A positive spin on Earth Day from WU

By: Jeff Masters and Bob Henson , 1:57 PM GMT on April 22, 2015

The challenges facing our global environment are serious indeed, but there are many smart people working on solutions, and there’s much to be optimistic about. At Weather Underground, we’re highlighting a wide range of these good-news stories in a special WU microsite created in honor of Earth Day. The theme is progress: through a collection of articles by researchers, field experts, and scientists, the microsite outlines the current state of our climate, how humans can adapt in coming years, and the various ways that we can minimize the damage to our planet's precious ecosystem.

Among the topics we cover:

--How climate change will influence food and wine production

--Why we needed Earth Day, and how it’s evolved since 1970

--The true cost of water: how water and energy are inextricably intertwined

--What a terrarium can teach us about the atmosphere, plus how to make your own

--How middle-school kids are using personal weather stations to learn about weather and climate

We invite you to dig into the microsite today as well as after Earth Day. It’s full of accessible information from experts and packed of engaging artwork and informative graphics. As is our tradition on Earth Day, we also present at the bottom of this post Dr. Jeff Masters' favorite wunderphotos uploaded to our web site over the past year. The Weather Underground staff has also put together an Earth Day gallery of 50 all-time awesome wunderphotos. Thanks go to everyone who has participated in making this the largest (1.8 million!) and best weather photo gallery on the Internet--your photos are truly an inspiration! Many of the choices were taken from our Worldview Gallery, updated weekly with the top wunderphotos of the week.

Jeff Masters and Bob Henson

Figure 1. Top wunderphoto of the past year: “Clouds to the Left", was taken on July 16, 2014 in Omaha, Nebraska, by wunderphotographer LarryD. Driving across Nebraska, it’s the scenery above that always impresses!

Climate Change

The Story Behind That Quadruple Rainbow

By: Bob Henson , 8:40 PM GMT on April 21, 2015

Social media lit up on Tuesday as a stunning photo of what appears to be a quadruple rainbow made the rounds. Amanda Curtis took the shot while waiting on a train at Glen Cove, NY, this morning. After she posted it to Twitter, the image quickly went viral. Curtis was interviewed over the phone by Jim Cantore and Sam Champion on The Weather Channel’s “AMHQ” program. As Curtis explained: “I was waiting for my commuter train into New York City and I was outside on the Glen Cove station platform and saw two double rainbows and was just absolutely blown away by it and decided to take the opportunity to snap the picture to use for later inspiration... I was outside and my train was coming, so I think I’m good under pressure and just decided to snap it and then run after the train.”

Figure 1. Amanda Curtis interviewed this morning on “AMHQ”. Image credit: The Weather Channel.

Figure 2. The tweet that sent cyberspace into rainbow heaven today. Image credit: Amanda Curtis.

At first, I was skeptical: the photo seem to run counter to everything I knew about atmospheric optics. Multiple rainbows can form due to reflections within the same raindrops that produce a single rainbow, but each iteration produces a fainter bow. The optics that produce each type are well-known. The arc of a single rainbow extends 41° around a line that runs from the sun through the observer’s head to the opposite side of the sky (the antisolar point). The closer to sunset it is, the higher in the sky the rainbow will appear. A double, or secondary, rainbow, forms a ring around the first rainbow, with an angle of 51° from the antisolar point. Secondary rainbows are fairly unusual, though I’ve seen a few. (See a good WunderPhoto example below.)

Even more rarely seen, and often disputed, are true triple and quadruple rainbows, which would appear on the other side of the sky--surrounding the sun, instead of opposite from it, and thus much harder to see. The first-ever scientifically vetted and verified photo of a pair of tertiary and quarternary (third- and fourth-order) rainbows were captured in Germany just four years ago, with the subsequent analysis published in the journal Applied Optics in 2011. And even more recently, a photographer in New Mexico captured the exceedingly faint fifth-order rainbow, which occurs in the slightly dimmed area called Alexander’s dark band between the primary and secondary bows.

Figure 3. Example of a primary (bottom) and secondary (top) rainbow. Image credit: wunderphotographer DI85.

What happened this morning in New York was a quite different phenomenon. A good analog is this Astronomy Picture of the Day, posted by NASA in 2007. It includes a standard single rainbow (the brightest) and secondary bow (arcing around the first one, toward the left), but also visible is a third bow that seems to connect the two. NASA explains: “This [third] rainbow is likely caused by sunlight that has first reflected off the lake before striking the distant raindrops that is reflecting sunlight back toward the observer. Each of these rainbows appears to be reflected by the calm lake, although because the positions of rainbows depend on the location of the observer, a slightly displaced image of each rainbow is actually being imaged.”

When I expressed initial doubt about today’s viral image, NOAA scientist and avid photographer Paul Neiman begged to differ. Paul pointed me to the NASA photo mentioned above, and provided this compelling explanation for the Glen Cove image:

“A typical primary rainbow is caused by refraction and one internal reflection of sunlight within raindrops, resulting in a rainbow that is positioned 41 arc degrees from the anti-solar point (i.e., the point directly opposite the sun – for example, if the sun is 10 degrees above the horizon at your back, the anti-solar point is 10 degrees below the horizon directly in front of you). The refraction causes the separation of white sunlight into its component colors, with red on the outside of the rainbow and violet on the inside. The secondary rainbow, which is centered 51 arc degrees from the anti-solar point (i.e., the larger of the two bows during a typical display), involves two internal reflections of sunlight within the raindrops rather than one, resulting in a reversal of the color sequence (red on the inside and violet on the outside). We can usually only see the portion of these rainbows above the horizon, because there isn’t a sufficient density of raindrops between the observer and the ground to see the rainbow below the horizon (exceptions include full-circle rainbows viewed from locales such as airplanes and mountain tops).

“So far, so good. For the much rarer reflected-light rainbows shown in this spectacular photo, a large glassy-smooth water surface is required behind the observer. This smooth water surface reflects the sun, such that a second solar light source is generated. This reflected sun, which is located the same the number of arc degrees below the horizon as the real sun is above the horizon, creates a second primary and secondary rainbow on the opposite side of the sky from the sun, but with the center of these reflected-light rainbows above the horizon. The geometry dictates that the regular and reflected-light rainbows will join at the horizon, as this photo suggests.”

Supporting Paul’s explanation is the fact that Oyster Bay sits a few miles east of where Amanda Curtis took the photo, so the morning sun could have reflected off a nearly calm bay, as noted by The Weather Channel’s Mark Elliot, before producing the rainbows captured by Curtis in the western sky. Readings from a Wunderground personal weather station at Oyster Bay showed that winds were nearly calm early this morning.

Special thanks go to Paul Neiman and to the Weather Channel’s Matt Sitkowski and Stu Ostro for informative discussions on this fascinating image.

Bob Henson

Figure 4. Another good example of a primary (bottom) and secondary (top) rainbow, taken on the Washington coast. Image credit: wunderphotographer 50something.


Carbon Dioxide Hits a New Peak this Spring: 404 ppm

By: Bob Henson , 2:08 PM GMT on April 21, 2015

Weekly carbon dioxide measurements from the pristine air atop Hawaii’s Mauna Loa have just topped another predictable yet worrisome milestone: 404 parts per million. The actual preliminary value reported by NOAA for last week (April 12–18) was 404.02 ppm. By all evidence, we now have the largest amount of CO2 present in Earth’s atmosphere for at least the last 800,000 years, and probably several million. The most prevalent of the human-produced greenhouse gases, carbon dioxide has been measured regularly by scientists at Mauna Loa since 1958. The gas is also measured at other sites around the world, but the Mauna Loa dataset is the most widely tracked index of global trends because of its uninterrupted 57-year length.

The weekly CO2 readings at Mauna Loa will crest over the next couple of months, making a run at 405 ppm before the annual seasonal decline begins (see below). Eyeballing the multiyear trend shown in Figures 1 and 2, it’s a fair guess that the final time we see a weekly value below 400 ppm will be somewhere toward the end of 2017, perhaps a year sooner or later. From that point on, we’re unlikely to again see a week below 400 ppm for many years—probably centuries, if not millennia—because of the ever-increasing accumulation of atmospheric CO2 produced by burning fossil fuels.

Figure 1. The last two years of daily, weekly, and monthly averages for carbon dioxide concentration measured by the Scripps Institution of Oceanography atop Mauna Loa, Hawaii. NOAA operates a parallel measurement program at Mauna Loa. Image credit: Scripps/The Keeling Curve.

What’s in a curve?
One of the most renowned images in climate science is the Keeling curve (see Figure 2), generated from the Mauna Loa data. This trace is famous for its inexorable year-to-year increase in CO2, as well as the seasonal rise and fall embedded in the graph’s sawtoothed pattern, a trait that became evident as early as 1960.

Figure 2. The Keeling Curve, 1958-present. Image credit: Scripps/The Keeling Curve.

Because the Northern Hemisphere has far more plant-friendly land mass than the Southern Hemisphere, it has an oversized impact on the global CO2 pattern. The result is a net global addition of carbon dioxide to the air as northern plants decompose, from around October till May, then a net removal as northern vegetation surges from roughly June through September. These natural seasonal spikes are about twice as large as the amount added each year by fossil-fuel burning, which has recently averaged just over 2 ppm per year. Unlike the human contribution, though, the seasonal spikes cancel each other out over time. After removing the seasonal cycle from the long-term record, we end up with a steady increase that topped 400 ppm for the first time in March, according to NOAA.

Close inspection of the the Keeling curve reveals some embedded nuance apart from the obvious seasonal cycle and the long-term rise. Figure 3 (below) shows how the percentage increase in carbon dioxide concentration at Mauna Loa varies from year to year. These bumps and dips arise from both natural and human factors.

Figure 3. The annually averaged growth rate of carbon dioxide, in parts per million, as measured at in the atmosphere at Mauna Loa. Horizontal black lines show the growth rate for each decade from the 1960s to 2000s. Image credit: NOAA Earth System Laboratory.

In a typical year, about 57% of the CO2 emissions put into the atmosphere by human activity remain in the air, showing up in the long-term measurements at Mauna Loa and elsewhere. The other 43% is removed by plants, soil, and oceans. These percentages have held remarkably steady over the long haul, but they can also vary markedly from year to year. El Niño, for example, tends to pinch off the cold equatorial upwelling that normally sends large amounts of CO2 into the air, thus causing a temporary drop in the overall global rate of increase.

The human contribution from fossil fuel also varies from year to year. Global emissions of carbon dioxide actually dropped slightly during the recession years of 1992 and 2009. Likewise, CO2 emissions tend to increase at a faster clip when the global economy is especially robust. Policymakers have long taken this connection between emissions and economic activity for granted. Many were surprised, then, when global CO2 emissions in 2013 came in essentially flat even though the world’s gross domestic product had risen by about 3%. This could be a one-year fluke--scientists and policy experts have been debating this point--but it’s also a hopeful sign that our global economic engine just might be able to run on less coal, oil, and gas while still performing well.

The long view
How high the concentrations get in this century and beyond will depend in large part on what measures the global community takes to restrict carbon emissions, including any agreements hammered out at the crucial UN climate meeting in Paris this December. Technology is a huge player, of course: wind and solar power, hydropower, and nuclear power are all close to carbon-neutral when compared to fossil fuels. But unless a price is set on carbon through some globally accepted process, there will be powerful market incentives for a growing world to use as much of our existing reserves of oil, coal, and natural gas as possible. And a key insight vividly highlighted by author and activist Bill McKibben remains: Earth holds several times more fossil fuel than needed to push global warming above the 2°C benchmark widely accepted as a target to minimize the odds of major climatic disruption.

Bob Henson

Figure 4. Atmospheric carbon dioxide concentrations derived from ice cores (prior to 1958) and Mauna Loa data (from 1958 onward) show the rises and falls associated with several ice ages and the dramatic spike of the last 100 years. Image credit: Scripps/The Keeling Curve.

Climate Change

Isis, Odile Removed from Northeast Pacific Tropical Cyclone List

By: Jeff Masters and Bob Henson , 1:18 PM GMT on April 20, 2015

The Northeast Pacific list of hurricane names got a shake-up on Friday, when the U.N.'s World Meteorological Organization (WMO) voted to remove the name "Isis" because of its potential confusion with the Islamic militant group, the Islamic State of Iraq and ash-Sham (ISIS). Isis is the name of an ancient goddess of Egypt, and was scheduled to be used in the Northeast Pacific (also called the Eastern North Pacific by WMO) in 2016. The ISIS militant group has been accused by U.N. war crimes investigators of committing brutal atrocities against civilians during a bloody conquest of large portions of Syria and Iraq over the past two years. The WMO Hurricane Committee for Region IV (North America/Central America/Caribbean), composed of experts from 27 member states and territories, met in in Costa Rica last week and elected to replace the name "Isis" with "Ivette". It is rare but not unprecedented for a name to be removed from the list of hurricane for reasons other than retirement due to death and destruction. Both "Adolph" and "Israel" were removed from the Northeast Pacific hurricane list for reasons of sensitivity in 2001.

Figure 1. MODIS satellite image of Hurricane Odile approaching the tip of Mexico's Baja Peninsula, taken at approximately 4:30 pm EDT Sunday September 14, 2014. At the time, Odile was a Category 3 storm with 125 mph winds. Image credit: NASA.

Hurricane Odile's name retired
One other Northeast Pacific name was removed from the list of hurricanes for that basin during last week's meeting: Odile. Hurricane Odile roared ashore near Cabo San Lucas as a Category 3 storm with 125 mph winds on September 25, 2014, and was the strongest storm on record to hit Baja. The storm killed eleven and did $1.22 billion in damage, making it the 6th most expensive Northeast Pacific hurricane ever. "Odile" will be replaced by "Odalys", which will appear on the list of names for the 2020 season. Odile is one of only thirteen hurricanes in the Northeast Pacific to get its name retired since naming began in 1960.

For the first year since 2009, no Atlantic names were retired in 2014. If we manage to go without retiring a hurricane name in 2015, it will be the first time since 1993 - 1994 that the Atlantic will have gone back-to-back years without a retired hurricane (thanks to wunderground member Mark Cole for pointing out that Ingrid was retired in 2013, which I overlooked originally.) Overall, hurricanes in the North Atlantic have a much better chance than those in the Northeast Pacific of reaching shore and inflicting enough damage to prompt a name’s retirement. Since the Atlantic’s current naming system began in 1954, a total of 79 names have been retired. Some intriguing randomness shows up in the alphabetic arrangement of the Atlantic’s retired names. As you might expect, there’s a greater concentration toward the first part of the alphabet, but the pattern is far from linear. Seven “A” and “D” storms, eight “F” storms, nine “C” storms, and ten "I" storms have been put on the shelf--but only three “B” and three “E” storms. The name “Janet” was retired in 1955, but it took until 1990 for a “K” name (Klaus) to be put on the shelf. Once the North Atlantic entered its current era of intensified activity in 1995, retirements began to surge through the alphabet, reaching all the way to “Wilma” in 2005.

Tornado activity remains at a near-record slow pace
Severe weather dotted the southern Plains from Thursday through Saturday before spreading across the South on Sunday. Hail and high winds made up the bulk of the action, although a few short-lived tornadoes were reported. Two twisters with preliminary EF1 ratings brought down numerous trees and caused some structural damage in east central Alabama on Sunday, and another EF1 was reported in southwest Louisiana on Saturday. Several highly visible tornadoes spun across the eastern Texas Panhandle and far western Oklahoma on Thursday, causing little damage.

Figure 2. Cumulative tornado activity through April 18 is running at close to a record-slow slow pace, as tracked by the NOAA Storm Prediction Center’s “inflation-adjusted” database. Image credit: NOAA/SPC.

Despite the high-profile EF4 tornado in Illinois on April 9, the nation continues to be experiencing one of its quietest tornado seasons on record. The preliminary total for January 1 through April 18 is 112, just barely above the record low of 109 for the “inflation-adjusted” database kept by NOAA’s Storm Prediction Center. (These data are adjusted to correct for the rise in tornado reports over recent decades produced by greater observing.) The slow-moving upper low that triggered severe weather this past weekend should generate a parting round of intense storms across the mid-Atlantic on Monday. Attention will then shift back to the south-central states by midweek, as an upper low rides in on a strong subtropical jet stream.

Jeff Masters and Bob Henson

Figure 3. A thunderstorm-generated shelf cloud near Mounds, OK, on Sunday, April 19. Image credit: wunderphotographer mrwing.


March 2015: Another Warmest Month on Record for the Planet

By: JeffMasters, 4:15 PM GMT on April 17, 2015

March 2015 was Earth's warmest March since global record keeping began in 1880, said NOAA's National Climatic Data Center (NCDC) on Friday. NASA rated March 2015 as the 3rd warmest March on record (small differences in analysis techniques can lead to slightly different rankings from agency to agency, and the two estimates were quite close to each other.) March 2015's warmth makes the year to date period (January - March) the warmest such period on record, and the past twelve months the warmest twelve-month period in recorded history. By NOAA's reckoning, seven of the past eleven months (May, June, August, September, October, and December 2014, along with March 2015) have tied or set new record high monthly temperatures. According to NASA, March 2015 had the 5th largest departure from average for warmth of any month in recorded history. Out of the ten months with the largest departures from average in the NASA database, five have occurred in the past year:

Jan 2007, 0.93°C above average
Mar 2002, 0.88°C above average
Mar 2010, 0.87°C above average
Feb 1998, 0.86°C above average
Mar 2015, 0.84°C above average
Apr 2010, 0.82°C above average
Sep 2014, 0.81°C above average
Feb 2015, 0.78°C above average
May 2014, 0.78°C above average
Oct 2014, 0.77°C above average

Figure 1. Departure of temperature from average for March 2015, the warmest March for the globe since record keeping began in 1880. Record warmth was observed in parts of the western United States and Canada, various regions in eastern Africa, parts of Scandinavia and northwestern Russia, part of south central China, and an area of northeastern Australia. Record cold was not observed over any land areas. Image credit: National Climatic Data Center (NCDC) .
Global ocean temperatures during March 2015 were the 3rd warmest on record, and global land temperatures were the 2nd warmest on record. Global satellite-measured temperatures in March 2015 for the lowest 8 km of the atmosphere were the 9th or 5th warmest in the 37-year record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively.

Figure 2. Cars are covered under the part of a metal roofing in Prague on March 31, 2015, as the Czech Republic and many other parts of northern Europe are hit by extreme winds. Image credit: MICHAL CIZEK/AFP/Getty Images.

One billion-dollar weather disaster in March 2015: European windstorms Mike and Niklas
One billion-dollar weather-related disaster hit the Earth last month, according to the March 2015 Catastrophe Report from insurance broker Aon Benfield: back-to-back severe windstorms (Mike and Niklas), which pounded western and central Europe from March 29 - April 1. The storms killed at least nine people and did approximately $1 billion in damage. Hurricane-force winds, including a peak gust of 192 kph (120 mph), hit parts of Germany, the UK, Netherlands, Switzerland, Austria, and Poland. The European windstorm and the February 16 - 22 U.S. winter storm ($1.9 billion in damage) have been the only billion-dollar weather disasters of 2015, as tallied by Aon Benfield. Two other natural disasters during May 2015--landfalls by two separate Category 5 tropical cyclones in Vanuatu and the Federated States of Micronesia--may end up being the most expensive disasters in those nations' history (see below.) The deadliest disaster of March 2015 was an extreme flood in Chile's Atacama Desert, which left 111 people dead or missing.

Figure 3. Tropical Cyclone Pam as seen by the VIIRS instrument on the Suomi satellite at 10:42 am EDT March 13, 2015. At the time, Pam was a Category 5 storm with 165 mph winds, and was just southeast of Efate Island, where the capital of Vanuatu, Port Vila, lies. Image credit: @NOAASatellites.

Tropical Cyclone Pam: Vanuatu’s worst natural disaster on record?
Category 5 Cyclone Pam blasted the South Pacific island nation of Vanuatu on Friday the 13th of March 2015 with maximum 1-minute sustained winds of 165 mph winds, making it one of only ten Category 5 storms ever rated by the Joint Typhoon Warning Center (JTWC) in the waters east of Australia. The official tropical cyclone warning center for the area, the Fiji Meteorological Service, estimated that Pam's central pressure bottomed out at 896 mb, making it the second most intense tropical cyclone in the South Pacific basin after Cyclone Zoe of 2002. At least eleven were killed, 132,000 people impacted, and damages were at least $100 million. According to EM-DAT, the international disaster database, the only comparable disaster in Vanuatu's history occurred in January, 1985 when twin Category 3 storms--Eric and Nigel--battered the nation, affecting 118,000 people and doing $173 million in damage. By April 10 2015, estimated that 110,000 people in Vanuatu still had no access to safe drinking water, and 6,000 people were still living in makeshift or temporary shelters.

Figure 4. One of the most spectacular images ever captured of a tropical cyclone from space: Category 5 Super Typhoon Maysak as seen from the International Space Station at approximately 6 pm EDT Tuesday March 31, 2015 (just after dawn local time.) At the time, Mayask had top winds of 160 mph as estimated by the Joint Typhoon Warning Center, and a central pressure of 905 mb, as estimated by the Japan Meteorological Agency.  At its peak strength, the Japan Meteorological Agency (JMA) put Maysak's central pressure at 905 mb, the lowest pressure they have estimated for any typhoon occurring so early in the year (previous record: 930 mb.) Image credit: Terry W. Virts.

Typhoon Maysak: one of Micronesia's most expensive natural disasters in history
With damage in the millions, nine dead, and over 6,000 people homeless, the  March 29 - April 1 rampage of Typhoon Maysak through the Federated States of Micronesia ranks as one of the worst disasters in their history. Maysak passed through the Chuuk State of Micronesia as a Category 1 typhoon, and Maysak's southern eyewall passed over the sparsely populated islands of Fais and Ulithi in the Yap State of Micronesia while the storm was at Category 5 strength.  Most structures on Ulithi not made of concrete were damaged or destroyed by Maysak's powerful winds. The entirety of the island's crop were ruined by the typhoon's storm surge, with early estimates indicating that it would be a full year before crops could be planted again, due to salt water intrusion. The nine people killed by the storm made it Micronesia's second deadliest storm in recorded history, according to EM-DAT. Their deadliest disaster was Category 4 Typhoon Chataan, which dumped 19.90" (506 mm) of rain in 24 hours on Chuuk, causing landslides that killed 47 people. The most expensive disaster in Micronesia's history was Category 1 Typhoon Nina, which did $6 million (1987 dollars) in damage on November 21, 1987.

Video 1. The deadliest disaster of March 2015 was flooding in the driest part of the world—Chile’s Atacama desert, on March 23 - 26, 2015. As of April 13, there were 111 people dead or missing from the disaster. According to EM-DAT, this would rank as Chile's 3rd deadliest flood in recorded history. The largest city in the region, Antofagasta, received a deluge of 24.4 mm (0.96 inches) in 24 hours—over fourteen years of rain in one day! This video shows incredible flooding in Chanaral, Chile, on March 25, 2015 from the deluge. A better version of this video with sound is available on Facebook.

El Niño continues in March 2015
NOAA maintained its El Niño advisory during March 2015, as weak El Niño conditions continued in the equatorial Eastern Pacific. Sea surface temperatures were 0.7°C above average on April 13 in the so-called Niño 3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for an El Niño event to be declared. NOAA is giving a 70% chance of El Niño lasting through summer.
Arctic sea ice falls to lowest March extent on record
Arctic sea ice extent during March 2015 was the lowest in the 36-year satellite record, according to the National Snow and Ice Data Center (NSIDC). As of April 16, sea ice extent was the 3rd lowest on record for this time of year, behind 2007 and 2006, according to The University of Illinois Cryosphere Today.
Notable global heat and cold marks set for March 2015
Hottest temperature in the Southern Hemisphere: 46.5°C (115.7°F) at Birdsville, Australia, March 19
Coldest temperature in the Southern Hemisphere: -74.4°C (-102.5°F) at Dome A, Antarctica, March 31
Hottest temperature in the Northern Hemisphere: 44.5°C (112.1°F) at Hudeiba, Sudan, March 29
Coldest temperature in the Northern Hemisphere: -55.2°C (-67.4°F) at Delyankir, Russia, March 5

Major stations that set new all-time heat or cold records in March 2015
Saint Brandon, Saint Raphael Island (Cargados) (Mauritius), max. 35.4°C  March 2
Cape Town (South Africa), max. 42.4°C, March 3
Cape Point (South Africa), max. 39.3°C, March 3
Robertson (South Africa), max. 44.0°C, March 3
Jonkershoek (South Africa), max. 42.8°C, March 3
Bata (Equatorial Guinea), max. 35.5°C, March 18
Santiago Pudahuel Int. Airport (Chile), max. 36.8°C, March 20
Arturo Prat (Antarctica), max. 11.3°C, March 23
Marambio Base (Antarctica), max. 17.4°C,  March 23
Esperanza (Antarctica), max. 17.5°C, March 24
Zamboanga (Philippines), max. 37.0°C, March 31

New all-time national and territorial heat records set or tied in 2015
So far in 2015, five nations or territories have tied or set all-time records for their hottest temperature in recorded history. For comparison, only two nations or territories did so in 2014, and nine did in 2013. The most all-time national heat records in a year was nineteen in 2010 (21 records at the time, but two have been broken since.) Since 2010, 46 nations or territories (out of a total of 235) have set or tied all-time heat records, and four have set all-time cold temperature records. Since each of those years ranked as one of the top twelve warmest years in Earth's recorded history, this sort of disparity in national heat and cold records is to be expected. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. I use as my source for international weather records Maximiliano Herrera, one of the world's top climatologists, who maintains a comprehensive list of extreme temperature records for every nation in the world on his website. If you reproduce this list of extremes, please cite Maximiliano Herrera as the primary source of the weather records. Wunderground's weather historian Christopher C. Burt maintains a database of these national heat and cold records for 235 nations and territories on's extremes page. Here are the national heat and cold records set so far in 2015:

Ghana set a new national heat record of 43.3°C (109.9°F) at Navrongo on April 10. This is the third time this year Ghana has tied or set a new all-time heat record. Previous records:  43.1°C (109.6°F), set the previous day, on April 9, and 43.0°C (109.4°F) on February 12.
Antarctica set a new territorial heat record of 17.5°C (63.5°F) at Esperanza Base on March 24. Previous record: 17.4°C (63.3°F) at Marambio Base, set the previous day. The World Meteorological Organization (WMO) has appointed a committee to study this event and determine if this represents an official record for the continent.
Equatorial Guinea set a new national heat record of 35.5°C (95.9°F) at Bata on March 17. Previous record:  35.3°C (95.5°F) at Malabo in February 1957.
Wallis and Futuna Territory (France) set a new territorial heat record with 35.5°C (95.9°F) on January 19 at Futuna Airport.
Samoa tied its national heat record with 36.5°C (97.7°F) on January 20 at Asau. Previously record: same location, in December 1977.

Climate Change Bumper Sticker Contest
It's time to sharpen your pencils, cudgel your brains, and consult your muse: the National Center for Science Education (NCSE) is running a bumper sticker contest! This is your chance to help to spread the word about climate change education. Your brilliant idea could end up on the tail end of thousands of cars. Your climate change-themed bumper sticker can be funny, fierce, fiery--as long as it's good. The details: Submissions will be accepted through May 31, 2015.

This week’s WunderPoster: Penitentes
The finely sculpted ice features known as penitentes are featured in the latest installment in our WunderPoster series (Figure 5, right). Charles Darwin wrote about penitentes in 1839 after a visit to the Andes, where the formations are especially common. In very dry high-altitude conditions, such as those found in the Andes, snow crystals often enter the atmosphere directly as water vapor (sublimation) rather than first melting into water. Random features on the snow surface, such as pockets of dust or soot, can affect the rate of sublimation and lead to a patchwork effect. The resulting depressions concentrate sunlight, further hollowing out the snow and leaving behind the majestic spires, which can range from a few inches up to 15 feet tall.

Penintentes draw their name from the spires’ resemblance to the tall hoods worn by religious figures during the penance processions of Spanish Holy Week.

All WunderPosters can be downloaded in formats suitable for posters or postcards.

Have a great weekend, everyone!

Jeff Masters and Bob Henson

Climate Summaries

CEOs Urging Action in 2015 on Global Climate

By: Jeff Masters and Bob Henson , 11:24 PM GMT on April 16, 2015

In an open letter released on Thursday evening, 43 chief executive officers from leading global companies called on governments around the world to take bold action at the pivotal UN climate meeting set for later this year. The CEOs are listed in a full-page ad appearing in Friday’s issue of Financial Times (see image below), in conjunction with the spring meetings of the World Bank Group and International Monetary Fund. The signatories to the letter include David Kenny, chairman and CEO of The Weather Company, the umbrella organization that includes Weather Underground. “Climate change is one of the biggest global challenges that will shape the way we do business now and in the coming decades,” the CEOs stated. “We extend an open offer to national governments to meet and co-design tangible actions as well as ambitious, effective targets that are appropriate for their different jurisdictions.”

Looking toward a post-Kyoto climate deal
Representatives from around the world will meet in Paris this December for the 21st UN Conference of Parties (COP21), a product of the 1992 UN Framework Convention on Climate Change that was signed by U.S. President George Bush and the heads of 164 other nations. Delegates in Paris will be working toward a new global agreement on carbon emissions to succeed the Kyoto Protocol, whose initial phase expired in 2012. The CEOs’ open letter outlines their shared vision for a successful climate deal at COP21, as well as their companies’ commitments to reduce their environmental and carbon footprints, serve as climate action ambassadors, manage climate risks, and help strengthen societal resilience to climate change.

The coalition of CEOs is facilitated by the World Economic Forum, the Swiss nonprofit organization that holds a high-profile annual meeting in Davos each year. The 43 companies involved in the coalition represent more than $1.2 trillion in revenue earned in 2014 from operations in more than 150 countries and territories.

“Hastening the shift to a low-carbon economy in an economically sustainable manner will generate growth and jobs in both the developing and developed world. Delaying action is not an option--it will be costly and will damage growth prospects in the years to come,” states the open letter. “The CEO Climate Leaders call on government leaders and policy makers to align on global measures, to be consistent in policy-making and to develop helpful innovation frameworks. A comprehensive, inclusive and ambitious climate deal in Paris on mitigation, adaptation and finance--in combination with a strong set of clear policy signals from the world’s leaders--is key to accelerating this transition. This opportunity should not be missed.”

Weather Underground’s position on climate change
“Based on the evidence, more than 97% of climate scientists have concluded that human-caused climate change is happening. Climate change is already causing significant impacts to people and ecosystems, and these impacts will grow much more severe in the coming years. We can choose to take economically sensible steps to lessen the damage of climate change, and the cost of inaction is much higher than the cost of action.”

See our recent blog posts for more on global climate in 2014--the warmest year on record--and what the next few years may bring.

Jeff Masters and Bob Henson

Climate Change Politics

Dust and Deluge: Heavy Rain in Southeast, High Winds and Grit in Rockies, Plains

By: Bob Henson , 3:36 PM GMT on April 15, 2015

A series of drenching rains across much of the South this week is being fed by some of the richest atmospheric moisture on record for April. Flash flood watches and flood warnings are plastered across much of the central Gulf Coast, where pockets of 3+” of rain on Tuesday followed widespread 1 – 2” amounts on Monday. CoCoRaHS reports for the 24-hour period ending Wednesday morning included 5.08” in Hancock County, Mississippi, and 4.94” in St. Tammany Parish, Louisiana. Flooding has been minimal so far across the Gulf Coast, with soil moisture lower than average going into the week’s rains. That’s not the case in already-sodden Kentucky, where yet more heavy rain on Tuesday sent a number of streams and rivers into flood stage. Lexington and Frankfurt have already secured their second wettest April on record, with more than two weeks left to go. Both cities need less than 2” to vault into top-five status for their all-time wettest months.

Figure 1. Departure from average rainfall for the period April 1 – 14. A large part of Kentucky is 5” to 8” above average for the first two weeks of the month. Image credit: National Weather Service/Louisville.

The heavy showers and thunderstorms across the South are being goosed by a strong subtropical jet stream that’s very prototypical of El Niño. NOAA’s spring outlook, issued on March 15, highlighted the potential for unusually heavy rains in the Southeast. The jet dynamics will be reinforced late this week into the weekend ahead of a strong upper-level low that will be sinking into the southern Rockies and moving slowly east across Texas. The 5-day precipitation forecast from NOAA’s National Centers for Environmental Prediction shows widespread 3 – 5” amounts from Texas to the Carolinas.

Figure 2. Projected 5-day precipitation amounts for the period from 1200 GMT Wednesday, April 15, to Monday, April 20. Image credit: NOAA/NCEP/Weather Prediction Center.

There’s plenty of juice on hand for the atmosphere to work with, as vertical profiles show very high amounts of precipitable water (PW) for this time of year. (Precipitable water is the amount of rain that would fall at a given point if all of the moisture in the air above it were squeezed out.) At New Orleans, the PW value measured by radiosonde at 1200 GMT Monday hit 1.96”, not far from the April record of 2.09”. Morehead City, NC, reported 1.86” of PW at 0000 GMT Tuesday, just short of the April record of 1.92”.

Big snow possible in Colorado
Heavy precipitation of a different sort may plaster higher elevations of the Colorado Front Range late this week. After several days of stark disagreement among major computer models, there’s now more consensus that the upper low mentioned above will move very slowly through the southern Rockies on Thursday and Friday, producing a long period of favorable easterly winds blowing upslope against the Rockies. Temperatures in most of the Denver/Boulder area may end up a shade too high for major snow, but foothills and higher peaks just to the west (where a winter storm watch is now in effect) could easily see a foot or more of wet spring snowfall. Some of the heaviest snows in the Denver/Boulder area occur during spring and fall when El Niño conditions are in place, as slow-moving upper lows are especially prone to develop then. UCAR’s Matt Kelsch has just updated a blog that I posted on this topic in 2009, examining the heaviest Boulder snows since 1950. The new stats show that of the 14 storms that have produced at least 20” of snow in Boulder, eight occurred during El Niño periods, but just two during La Niña events, with the other six during neutral conditions. Wunderground weather historian Christopher C. Burt has a more general look at Record April Snowstorms in a post from 2013.

Figure 3. A wildfire looms just beyond the campus of the University of Mary in Bismarck, North Dakota, on Monday evening, April 13. The fire flared up again on Tuesday, moving even closer to campus. Image credit: Kyle W. Martin.

Wind, dust, and fire out West
Strong westerly flow pushed mild, dry air across the northern Rockies and Plains into the Midwest on Tuesday. Chicago tied its all-time lowest relative humidity of 13% on Tuesday afternoon, with temperatures in the 60s and dew points in the teens. (Thanks go to Dave Schwartz of The Weather Channel for this tidbit.) The parched air sent fire weather conditions to extreme levels over the Dakotas, with similar conditions expected over the Southwest and southern High Plains on Wednesday. At Bismarck, ND, the University of Mary was evacuated Tuesday afternoon when a grass fire came perilously close to campus (see Figure 3 above).

Figure 4. Officials inspect the scene of an accident on Interstate 80 west of Salt Lake City on Tuesday, April 14. Howling winds halted flights at Salt Lake City's airport and toppled semitrailers on I-80, causing authorities to close a 100-mile stretch of northern Utah's main east-west highway. Image credit: Scott G. Winterton/The Deseret News via AP.

A powerful cold front and strong surface flow just ahead of it pushed dust across a large swath of the West. Widespread 60 – 80 mph wind gusts were reported by Utah mesonet stations, and power was knocked out for thousands of Utahns. Several vehicles were blown off Interstate 80, and a major pile-up amid the dust killed at least one person and injuring 25. In Salt Lake City, the front pushed temperatures from a springlike 75°F at 2:30 pm to a raw 35°F with light snow by 6:30 pm. Visibility was briefly down to a half mile just after the front hit. An 2012 analysis led by James Steenburgh (University of Utah) shows that Salt Lake City averages 4 -5 dust storms per year that reduce visibility to 10 miles or less. Only about 2% of these storms push visibility below 0.5 mile, suggesting that this was a roughly once-in-a-decade event. GOES-13 satellite images captured the frontal passage and the associated dust over California and Nevada.

Figure 5. A man tries to save his house from fires spreading from neighboring homes in the Siberian village of Smolenka, near Chita, on Monday, April 13. Russian authorities say out-of-control agricultural fires have killed or injured hundreds and destroyed or damaged more than 1,000 homes. The fires were started by farmers burning the grass in their fields, but spread quickly because of strong winds. Image credit: AP Photo/Evgeny Yepanchintsev.

April is off to a dusty, smoky start in parts of Asia, Europe
Dust and fire have made their mark over an unusually large swath of Eurasia over the last few days. A massive, eerie dust storm, apparently one of the most intense in years for Dubai, swept from the Arabian Peninsula to India, as chronicled in Tom Yulsman’s ImaGeo blog on April 8. To the north, the normal seasonal burning of fields by farmers in the Khakassia province of far south Siberia turned disastrous early this week amid high winds and dry, record-warm air. At least 23 people were killed, with close to 1000 seeking medical help and an estimated 5000 left homeless. Intense dust and sand storms have also been reported this week in Ukraine and Belarus, closing several airports, and strong southerly winds pushed Saharan dust as far as southern England, adding to poor air quality in London.

Temperatures this winter (December – February) ran far above average throughout most of Europe and Asia. Jeff Masters will have a full report on national and global climate for March at the end of this week.

Bob Henson

Figure 6. Conditions in Salt Lake City at the height of Tuesday’s dust storm.
Image credit: wunderphotographer hurricanes2018.

Dust Storm Flood

CSU Predicts a Quiet 2015 Atlantic Hurricane Season Due to Rising El Niño Odds

By: Jeff Masters , 2:05 PM GMT on April 13, 2015

Another quiet Atlantic hurricane season is likely in 2015, said the hurricane forecasting team of Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU) in their latest seasonal forecast issued April 9. They called for an Atlantic hurricane season with 7 named storms, 3 hurricanes, 1 intense hurricane, and an Accumulated Cyclone Energy (ACE) of 40. The long-term averages for the period 1971 - 2010 were 12 named storms, 6.5 hurricanes, 2 intense hurricanes, and an ACE of 92. The 2015 forecast calls for a below-average chance of a major hurricane hitting the U.S., both along the East Coast (15% chance, 31% chance is average) and the Gulf Coast (15% chance, 30% chance is average). The Caribbean is forecast to have a 22% chance of seeing at least one major hurricane (42% is average.) Five years with similar pre-season February and March atmospheric and oceanic conditions were selected as "analogue" years that the 2015 hurricane season may resemble: 2014 (which featured 8 named storms, 6 hurricanes, and 2 intense hurricanes); 1993 (8 named storms, 6 hurricanes, and 2 intense hurricanes); 1991, featuring Hurricane Bob, which hit Long Island, New York as a Category 2 storm; 1987 (7 named storms, 3 hurricanes, and 1 intense hurricane); and 1957, which featured the deadliest June hurricane on record, Hurricane Audrey, which killed 416 people in Texas and Louisiana. These five years all had at least moderate El Niño conditions and cool Sea Surface Temperatures (SSTs) in the tropical Atlantic. The average activity for these years was 8 named storms, 4 hurricanes, and 2 major hurricanes.

Figure 1. Hurricane Gonzalo as seen from the International Space Station on October 16, 2014. At the time, Gonzalo was at peak strength, with 145 mph winds, and was the first Atlantic hurricane to reach sustained winds of at least 145 mph since Hurricane Igor of 2010. Gonzalo hit Bermuda just a week after Hurricane Fay hit the island, and Gonzalo's remnants went on to batter the United Kingdom on October 21 with wind gusts exceeding 100 mph, killing three people there. Image credit: Alexander Gerst.

Why the forecast of a quiet season?
The CSU team cited two main reasons why this may be an quiet hurricane season:

1) A weak El Niño event is underway in the Eastern Pacific, and is expected to intensify by this fall (see the discussion below in this post's last paragraph.) If El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. Sea surface temperatures were 0.7°C above average over the past week in the so-called Niño3.4 region (5°S - 5°N, 120°W - 170°W), where SSTs must be at least 0.5°C above average for five consecutive months (each month being a 3-month average) for a weak El Niño event to be declared. By August-October, most dynamical models are calling for a moderate El Niño (Niño 3.4 temperatures at least 1.0°C above average) or strong El Niño (Niño 3.4 temperatures at least 1.5°C above average). The European Centre for Medium-Range Weather Forecasts (ECMWF) shows the best prediction skill of the various El Niño/Southern Oscillation (ENSO) models, and the average of the various ECMWF ensemble members is calling for a strong El Niño event by September (a Nino 3.4 SST anomaly of approximately 1.7°C.)

2) Sea surface temperatures (SSTs) in the Main Development Region (MDR) for hurricanes from the Caribbean to the coast of Africa between 10°N and 20°N were much cooler than average in the eastern tropical Atlantic, and near average in the Caribbean in March 2015. Much of this unusual cooling was due to a persistent positive phase of the North Atlantic Oscillation (NAO) since November 2014. A positive phase of the NAO is associated with a strengthened Bermuda-Azores High and faster trade winds across the tropical Atlantic. The faster winds increase mixing of cool water to the surface. These cooler SSTs are associated with higher-than-normal sea level pressures which can create a self-enhancing feedback that relates to higher pressure, stronger trades and cooler SSTs during the hurricane season. Virtually all African tropical waves originate in the MDR, and these tropical waves account for 85% of all Atlantic major hurricanes and 60% of all named storms. When SSTs in the MDR are much above average during hurricane season, a very active season typically results (if there is no El Niño event present.) Conversely, when MDR SSTs are cooler than average, a below-average Atlantic hurricane season is more likely.

As always, they included the standard disclaimer with any quiet hurricane season outlook:

"Despite the forecast for below-average activity, coastal residents are reminded that it only takes one hurricane making landfall to make it an active season for them. They should prepare the same for every season, regardless of how much activity is predicted."

Figure 2. Departure of sea surface temperature (SST) from average for March 2015, as computed by NOAA/ESRL. SSTs in the hurricane Main Development Region (MDR) between Africa and Central America (red box) were well below average in the eastern Atlantic, and near average in the Caribbean.

How good are the April forecasts?
April forecasts of hurricane season activity are low-skill, since they must deal with the so-called "predictability barrier." April is the time of year when the El Niño/La Niña phenomenon commonly undergoes a rapid change from one state to another, making it difficult to predict whether we will have El Niño, La Niña, or neutral conditions in place for the coming hurricane season. Correctly predicting this is key, since if El Niño conditions are present this fall, this will likely bring about a quiet Atlantic hurricane season due to increased upper-level winds over the tropical Atlantic creating wind shear that will tend to tear storms apart. For now, these April forecasts should simply be viewed as an interesting research effort that has the potential to make skillful forecasts. The next CSU forecast, due on Monday, June 1, is the one worth paying attention to. Their early June forecasts have shown considerable skill over the years. NOAA issues its first seasonal hurricane forecast for 2015 on May 27.

TSR also predicts a below-average Atlantic hurricane season
The April 9 forecast for the 2015 Atlantic hurricane season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) also calls for a quiet season, but is not as low as CSU's forecast. TSR is calling for 11 named storms, 5 hurricanes, 2 intense hurricanes, and an Accumulated Cyclone Energy (ACE) of 56. The long-term averages for the past 65 years are 11 named storms, 6 hurricanes, 3 intense hurricanes, and an ACE of 102. TSR rates their skill level as low for these April forecasts--just 12 - 20% higher than a "no-skill" forecast made using climatology. TSR predicts a 25% chance that U.S. landfalling activity will be above average, a 25% chance it will be near average, and a 50% chance it will be below average. They project that 2 named storms will hit the U.S., with 1 of these being a hurricane. The averages from the 1950-2014 climatology are 3 named storms and 1 hurricane. They rate their skill at making these April forecasts for U.S. landfalls just 4 - 7% higher than a "no-skill" forecast made using climatology. In the Lesser Antilles Islands of the Caribbean, TSR projects 1 named storms and no hurricanes. Climatology is 1 named storm and less than 0.5 hurricanes.

TSR’s two predictors for their statistical model are the forecast July - September trade wind speed over the Caribbean and tropical North Atlantic, and the forecast August - September sea surface temperatures in the tropical North Atlantic. Their model is calling for cooler than average SSTs and faster than average trade winds during these periods, and both of these factors should act to decrease hurricane and tropical storm activity. Unlike CSU, TSR is not calling for an El Niño event this fall, which is giving them higher levels of activity in the Atlantic. They add: "Should the TSR forecast for 2015 verify it would mean that the ACE total for 2013-2015 was easily the lowest 3-year total since 1992-1994 and it would imply that the active phase of Atlantic hurricane activity which began in 1995 has likely ended." The next TSR forecast will be issued on May 27.

WSI predicts a quiet Atlantic hurricane season
The April 13 forecast from the private weather firm WSI (part of The Weather Company, along with The Weather Channel, Weather Central, and The Weather Underground), is calling for a quiet Atlantic hurricane season with 9 named storms, 5 hurricanes, and 1 intense hurricane. WSi cites the expectation of El Niño conditions to be present this fall as the reason for reducing their expected Atlantic hurricane season numbers from last month's forecast, which called for 10 named storms, 5 hurricanes, and 2 intense hurricanes.

NOAA increases El Niño odds to 60% for the fall
NOAA's monthly El Niño update issued on April 9 gives increased odds that the current weak El Niño event in the equatorial Eastern Pacific will stick around into fall. NOAA is now giving a 70% chance of El Niño lasting through summer, up from their 50 - 60% odds they gave a month ago. They give a 60% chance that El Niño will last though the fall. However, in a March 31 update, the Australian Bureau of Meteorology (BOM) cautioned: “Model outlooks spanning February to May . . . have lower confidence than forecasts made at other times of year. Some models currently show some spread in their outlooks for tropical Pacific Ocean temperatures, indicating that while further warming is indeed very likely, there remains some ambiguity about the amount of warming expected.” In his April 9 post, Wunderblogger Steve Gregory gave a 70% El Niño continuing into this winter, with a 30% chance that we would see a strong El Niño event.

Jeff Masters

Atmospheric Phenomena El Niño Hurricane

Tornadoes Rip Through Northern Illinois, Killing 2 and Injuring 20

By: Bob Henson and Jeff Masters , 1:28 PM GMT on April 10, 2015

America's worst severe weather outbreak so far in 2015 was Thursday, when a preliminary total of sixteen tornadoes touched down in Illinois, Iowa, and Missouri. Many of the tornado reports came from a single long-lived supercell in northern Illinois, about 80 miles northwest of Chicago, that spawned a large wedge-shaped tornado around 7 pm local time. Significant damage was reported near the town of Rochelle, and every structure in the tiny town of Fairdale was reportedly damaged or destroyed. Two people were killed in Fairdale, and twenty were injured.

Figure 1. Rochelle, Illinois tornado near Highways 64 & 251 on April 9, 2015. Image credit: Angie Medernach-Harris.

Figure 2. Radar reflectivity image of the supercell thunderstorm (circled in white) that spawned the Rochelle, Illinois, tornado at 6:55 pm CDT on April 9, 2015. The hook echo of the storm lies just northwest of the town, which is marked by a black circle. Image credit: Storm by Weather Underground.

Video 1. Impressive video of the large wedge tornado that hit Rochelle, Illinois on April 9, 2015.

The long-lived supercell that spawned the tornado formed in a nearly ideal location, ahead of a strong cold front plowing across Illinois and just south of a warm front that had moved to the WI/IL border. Some of the worst tornadoes on record have formed near the low pressure found at the intersection of these fronts, known as the “triple point”. Upper-level winds on Thursday were much stronger than on Wednesday, exceeding 100 mph in the midst of a compact jet-stream impulse that was heading into Illinois as the most damaging tornado developed (see Figure 3).

Figure 3.Winds at the jet-stream level (300 mb, or about 30,000 feet) at 0100 GMT Thursday, with icons denoting preliminary reports of tornadoes, severe hail, and severe wind as of late Wednesday night. Image credit: WunderMap.

Preliminary damage assessments put the tornado at EF4 strength with 180 - 200 mph winds, which would make it the first U.S. tornado of 2015 to be rated EF3 or stronger. Even if some homes were swept clean from their foundations, it would not automatically rank the tornado as an EF5 on the Enhanced Fujita Tornado Damage Scale, though. Unlike the original Fujita scale, EF rankings take into account the strength of a building’s construction. A violent tornado that struck Vilonia, Arkansas, on April 27, 2014, was rated as EF4 despite ripping homes from their foundations. NWS meteorologist John Robinson pointed out in an interview: “. . . If a house that has a foundation built with nuts, bolts, and appropriate-sized washers is swept away, leaving only the concrete foundation, the ‘expected value’ of wind in the Enhanced Fujita Scale is 200 mph, which puts it at the top of the EF4 category, not an EF5. It would have to be an exceptionally well-built house to go over 200 mph and thus achieve an EF5.”

While Thursday’s outbreak of tornadoes arrived relatively early in the season for northern Illinois, the Midwest is no stranger to early-spring twisters. It was on the same date (April 9) in 1953 that a radar in Champaign, IL, observed the first documented hook echo, a feature that soon became a hallmark of tornado detection. And this weekend (April 11-12) marks the 50th anniversary of the Midwest’s extremely violent 1965 Palm Sunday tornado outbreak. A total of 47 twisters killed 261 people, making it the fourth-deadliest outbreak in U.S. records behind only the Tri-State Tornado of 1925 and the Super Outbreaks of 1974 and 2011.

This week’s WunderPoster: The Brocken spectre
Avid mountain climbers might recognize the phenomenon featured in this week’s WunderPoster (Figure 4, right): the ghostly Brocken spectre. You might see it when standing atop a high point, looking down into fog or mist, with the early- or late-day sun behind you. Under these conditions, your shadow may appear against the mist, directly opposite the sun, surrounded by a faint rainbow-colored halo. It can be a startling sight, given that it’s hard to judge your shadow’s size if any nearby landmarks are obscured by the fog or mist. The spectre got its name from a peak named Brocken in Germany’s Harz Mountains. All WunderPosters can be downloaded in formats suitable for posters or postcards.

Bob Henson and Jeff Masters


Severe Weather Rumbles Eastward; Hail, Wind Widespread on Wednesday

By: Bob Henson , 7:36 PM GMT on April 09, 2015

Fast-moving thunderstorms were zipping across the Mississippi Valley on Thursday afternoon, as an upper-level storm accelerated through the region. NOAA’s Storm Prediction Center placed a large part of the Mississippi and Ohio Valleys and lower Great Lakes under an enhanced risk of severe weather for Thursday afternoon and evening (see Figure 1). The day’s first tornado watch was posted for northeast Missouri, southeast Iowa, and far northwest Illinois, effective until 8:00 pm CDT, with a second watch in effect until 11:00 pm CDT for most of northern Illinois and parts of extreme southern Wisconsin and far western Indiana. The strongest and longest-lived tornadoes typically form within discrete supercell thunderstorms, as opposed to squall lines or large thunderstorm clusters. If the line of storms in Iowa and Missouri becomes a solid squall line, the threat of strong tornadoes will diminish along it, but residents in its path should still be prepared for a burst of very heavy rain, high winds, and large hail, with brief tornadoes possible. Other storms could become supercells ahead of the line, particularly in northern Illinois.

Figure 1. Much of the central and eastern U.S. was at risk for severe weather on Wednesday afternoon and evening, April 9. Image credit: NOAA Storm Prediction Center.

Heavy rains and severe weather are again plaguing the Ohio Valley, which has endured several days of large thunderstorm complexes called mesoscale convective systems (MCSs) moving along a persistent east-west frontal zone. By Wednesday afternoon, the warm front had shifted to the southern Great Lakes, with temperatures ranging from 40s to its north to 60s and 70s just to its south. However, the final push of this week’s upper-level storm system may still bring one more round of severe storms and heavy rain across parts of Kentucky and West Virginia as well as southern Indiana and Ohio. A severe thunderstorm watch was issued Wednesday afternoon for the upper Ohio Valley, and a solid swatch of flash flood watches extend from the St. Louis area eastward to the Virginia/West Virginia border.

We’ll be covering the severe weather on Thursday afternoon and evening in our experimental Weather Underground live blog.

Figure 2. Preliminary data from NOAA’s Storm Prediction Center as of late Wednesday is overlaid here on the SPC convective outlook issued on Wednesday afternoon. A supercell thunderstorm in south-central Kansas produced eight tornado reports, with two others in southeast Missouri and western Oklahoma. Thanks to wunderground member TropicalAnalystwx13 for posting this overlay. Additional reports that came in after this graphic was produced can be found on the day’s SPC summary page. Data and imagery: NOAA Storm Prediction Center.

Wednesday’s storms: few tornadoes, but plenty of hail and high wind
The nation was spared major damage on Wednesday despite an extensive arc of severe weather from Texas to North Carolina. The most impressive storms were along the dry line from western Oklahoma into south-central Kansas. One long-lived supercell near the intersection of the dry line and the nation-straddling warm front produced several tornadoes near Medicine Lodge, KS. Storm chaser Mike Prendergast captured this impressive cone-shaped tornado near Deerhead, KS, with a faint rainbow visible. Another supercell dropped hail up to 3” in diameter in west-central Oklahoma. Large hail was the favored mode of the day’s severe weather, with more than 200 reports nationwide. Baseball-sized hail was reported in Missouri, Kentucky, and Indiana, as well as Oklahoma,

Figure 3. This hailstone in Sullivan, Missouri, was literally baseball-sized! Image credit: Hanna Findley.

Forecasters had correctly anticipated that the dry-line storms would be sparse but intense, although the coverage was even less than some had expected. Thin high clouds that overspread much of Kansas and Oklahoma cut down on daytime heating and reduced the available instability, which weakened the day’s severe potential somewhat. In addition, a layer of very warm, dry air atop the moist surface air served as a formidable cap for any thunderstorms attempting to draw on the surface air (although some less severe “elevated” thunderstorms did develop above the cap).

Jeff Masters will be posting an update on Friday covering NOAA’s latest El Niño projections and the seasonal hurricane forecasts issued this week by Colorado State University and Tropical Storm Risk.

Bob Henson

Figure 4. Mammatus clouds fill the sky near Slaton, TX, as thunderstorms prowl the Texas South Plains near Lubbock on Wednesday, April 8. Wind gusts as high as 76 mph and heavy blowing dust accompanied the storms. Image credit: Matt Mahalik, Texas Tech University.

Severe Weather

Significant Tornadoes Possible on Wed; Widespread Severe Weather Expected on Thursday

By: Bob Henson , 5:45 PM GMT on April 08, 2015

A batch of scattered but potent supercell thunderstorms should erupt late Wednesday afternoon and evening across parts of the central and southern Great Plains into the lower Missouri Valley. At 11:30 am CDT, NOAA’s Storm Prediction Center (SPC) placed a swath from roughly Wichita, KS, to Columbia, MO, under a moderate risk of severe weather for Wednesday, with lesser risk categories extending from northern Oklahoma to West Virginia. Significant tornadoes (EF2 - EF5 on the Enhanced Fujita Tornado Damage Scale) and very large hail (greater than 2” in diameter) are a possibility (see Figure 1).

Figure 1. As of 11:30 am CDT Wednesday, a large part of the central U.S. was under various risk categories for severe weather in the afternoon and evening (top). The crosshatched areas indicate the risk of significant tornadoes (center) and very large hail (bottom). The percentages in these two maps give the odds of a tornado (center) or hail of at least 1” diameter (bottom) occurring within 25 miles of a given point. Image credit: NOAA Storm Prediction Center.

This potential outbreak has been well predicted by forecast models for several days. Ample moisture and favorable jet-stream flow from the southwest have been in place since Monday, leading to a few pockets of severe weather already. SPC logged more than 50 preliminary reports of 1” to 2” diameter hail as far north as southern Minnesota, where moist air from the Gulf of Mexico flowed atop much chillier surface air. One complex of severe storms moved from eastern Missouri to Kentucky on Tuesday afternoon, dropping baseball-sized hail in the central Kentucky town of Garrard and dousing Louisville, KY, with another 1.21” of rain on top of the 14.62” it had already received since March 1. Damage surveys on Wednesday confirmed two tornadoes from this complex southeast of Lexington, KY, and two others were reported on Wednesday night in far southeast Kansas. Thunderstorms continued on Wednesday morning along and near a broad east-west frontal zone extending from central Missouri into southern Ohio, with two severe thunderstorm watches in effect by late morning.

A major upper low that gave much-appreciated snow and rain to California is now making its move into the central states, which will help trigger Wednesday’s main round of severe weather. A piece of energy from the low will sweep across a constellation of boundaries in the OK/KS/MO region. These included a dry line in northwest Oklahoma and the east-west frontal zone, which was pushed into northeast Oklahoma by late-evening storms on Tuesday, then began lifting back north into Kansas and Missouri as a warm front on Wednesday morning.

Scattered thunderstorms should form along or near these boundaries by Wednesday evening, with several rapidly becoming supercells that could spawn tornadoes. The sheer number of storms may be limited at first by a capping layer of warm, dry air several miles high. Weaker storms have formed above the cap in western Oklahoma, which may diminish the risk somewhat along the dry line. However, the amount of instability and wind shear on hand by evening, especially toward southeast Kansas and southwest Missouri, favors the emergence of supercells (long-lived, discrete thunderstorms that produce the lion’s share of stronger tornadoes). The cool low-level air pushed out from any storms that develop could provide boundaries for additional storm formation.

NOAA/SPC has issued a public severe weather outlook for Wednesday’s storms.

Figure 2. Wednesday’s severe weather will be followed by another round on Thursday, April 9. As shown above, the Wednesday 1200 GMT run of the high-resolution (4-kilometer) NAM model predicted that a line of potentially severe thunderstorms would bisect Illinois along a strong cold front at 7:00 pm CDT Thursday, with scattered intense storms from southern Michigan to western New York near a warm front. If overnight storms inhibit daytime heating on Thursday, the storms may be less widespread or severe. Once the Illinois storms form a solid line, the risk of significant tornadoes should lessen there, but a threat for high wind, heavy rain, and large hail would persist with the subsequent squall line into Indiana, Kentucky, and western Tennessee. Image credit: College of DuPage NeXt Generation Weather Lab.

Severe threat shifts to Midwest on Thursday
Tornadoes are also possible on Thursday as the upper low and associated frontal system accelerate northeast toward the Great Lakes. By afternoon, a strong cold front should be plowing east across Illinois, with the east-west frontal zone now sweeping north into Wisconsin and Michigan as a warm front. These boundaries will help focus intense thunderstorms across a broad area, probably more numerous than on Wednesday, with long-lived supercells possible. Wind shear will be stronger than on Wednesday, but it remains to be seen how well the atmosphere manages to recover from the cooling effect of Wednesday night’s storms upstream. If the air does warm up enough to become at least moderately unstable, models suggest that the powerful upper system could trigger a north-south line of fast-moving supercells across Illinois (see Figure 2), eventually becoming a solid line with heavy rain, hail, and high winds. Other dangerous storms may form along the warm front. The overall system’s increasing speed will put much of the Midwest and the Mississippi Valley in line for one or more quick shots of potentially severe weather. As of 12:30 p.m. CDT Wednesday, SPC’s enhanced-risk area for Thursday includes an unusually large swath from northeast Texas to eastern Ohio.

Figure 3. A partial double rainbow took shape near Taylorsville, KY, in the wake of the severe storms that produced at least two tornadoes and baseball-sized hail over central Kentucky. Image credit: wunderphotographer mlongteach.

Severe Weather

200 Years Ago This Week: Tambora's Eruption Causes a Planet-Wide Climate Emergency

By: JeffMasters, 5:33 PM GMT on April 07, 2015

Two hundred years ago this week, an obscure volcano in Indonesia named Tambora rumbled to life after centuries of dormancy. On April 5, 1815, huge plumes of fire jetted from the mountain for three hours, rocking the ground and painfully assaulting the ears of the local residents. But the eruption suddenly stopped, and the great mountain lapsed back into a fitful slumber. During the week that followed, Tambora sent occasional plumes of ash into the air, but most of the residents that had fled the initial eruption returned to farm the fertile soils on the flanks of the volcano. But on April 10, 1815, the mightiest volcanic explosion ever witnessed and recorded by humans rent Tambora in a cataclysmic eruption heard more than 1,200 miles (2,000 km) away. As recounted in Gillen D'Arcy Wood's excellent 2014 book, Tambora: The Eruption That Changed the World, "three distant columns of fire burst in cacophonous roar from the summit to the west, blanketing the stars and uniting in a ball of swirling flame. The mountain itself began to glow as stream of boiling liquified rock coursed down its slopes." Whole villages, totaling perhaps 10,000 people, were consumed by fiery pyroclastic flows. Tambora threw so much rock into the air that the mountain collapsed in on itself, chopping 9/10 of a mile (1.5 km) off the height of the mountain, and creating a massive caldera 4 miles (7 km) wide. The volcano's ash cloud covered an area nearly twice the size of the continental U.S., and at least 60,000 people died from the combined effect of Tambora's ash, pyroclastic flows, and tsunamis.

Figure 1. Aerial view of the caldera of Indonesia's Mount Tambora, formed during the colossal 1815 eruption. Image credit: Wikipedia.

Tambora creates a climate emergency
Tabora's eruption was a magnitude 7 event on the Volcanic Explosivity Index (VEI)--a "super colossal" eruption that one can expect to occur only once every 1000 years. The Volcanic Explosivity Index is a logarithmic scale like the Richter scale used to rate earthquakes, so a magnitude 7 eruption would eject ten times more material than the two largest eruptions of the past century--the magnitude 6 eruptions of Mt. Pinatubo in the Philippines (1991) and Novarupta in Alaska (1912).

The Tambora eruption threw so much sulfur dioxide (SO2) gas into the stratosphere that a "Volcanic Winter" resulted. Sulfur dioxide reacts with water to form sulfuric acid droplets (aerosol particles), which are highly reflective and reduce the amount of incoming sunlight. The sulfur pumped by this eruption into the stratosphere dimmed sunlight so extensively that global temperatures fell by about 0.4–0.7 °C (0.7–1.3 °F) for 1 - 2 years afterward, triggering the infamous Year Without a Summer in 1816. In Western Europe, summer temperatures in 1816 were up to 3°C (5.4°F) below average, resulting in crop yields that plunged more than 75%. Tens of thousands died of starvation, and tens of thousands more died in the typhus epidemic that followed. The situation was even more dire in India, where the eruption caused the failure of the monsoon rains from June through August 1816--the longest recorded break in the Southwest Monsoon in recorded history. The resulting famine and cholera epidemic that erupted ended up killing millions over the next few decades. Unprecedented July snows also hit Yunnan, China in 1816, resulting in widespread famine, and killing frosts in June, July, and August 1816 in Eastern Canada and New England caused widespread crop failures. A cold wave on June 5 - 11 dumped up to a foot of snow on the Northeast U.S., and lake and river ice were observed as far south as Pennsylvania in July and August.

Figure 2. Summertime temperatures in Europe during the summer of 1816 were up to 3°C (5.4°F) below average over France, Switzerland, and Spain. Image credit: Giorgiogp2 on Wikipedia Commons.

Figure 3. A promotional photo of Boris Karloff as Frankenstein's monster, using Jack Pierce's makeup design. The failure of the Southwest Monsoon in 1816 due to the ash cloud from Tambora caused storm tracks over Western Europe to shift to the south, and recurrent low pressure systems brought cold air and heavy and long-lasting rainfall to western and central Europe. While trapped indoors for weeks by constant rain and gloomy skies during her vacation at Lake Geneva in Switzerland during the summer of 1816, Mary Shelley was inspired to write Frankenstein, a horror novel set in an often stormy environment. Image credit: Wikipedia.

Magnitude 7 Super-colossal eruptions
In an article published in 2008 in the American Geophysical Union journal EOS, Dr. Ken Verosub of the University of California, Davis Department of Geology estimated that future eruptions capable of causing "Volcanic Winter" effects severe enough to depress global temperatures by 2°F (1°C) and trigger widespread crop failures for 1 - 2 years afterwards should occur about once every 200 - 300 years. Even a magnitude 6 eruption, such as the 1600 eruption of the Peruvian volcano Huaynaputina, can cause climatic change capable of killing millions of people. The Huaynaputina eruption is blamed for the Russian famine of 1601-1603, which killed over half a million people and led to the overthrow of Tsar Boris Godunov. Thankfully, the climatic impacts of all of these historic magnitude 6 and 7 eruptions have been relatively short-lived. After about two years, the sulfuric acid aerosol particles have settled out of the stratosphere, returning the climate to its former state.

Magnitude 8 Mega-colossal eruptions
Even more extreme eruptions have occurred in Earth's past--eruptions ten times more powerful than the Tambora eruption, earning a ranking of 8 out of 8 on the Volcanic Explosivity Index (VEI). These "mega-colossal" eruptions occur only about once every 10,000 years, but have much longer-lasting climatic effects and thus are a more significant threat to human civilization. A mega-colossal eruption at Toba Caldera, Sumatra (Indonesia), about 74,000 years ago, was 3500 times greater than the Tambora eruption. According to model simulations, an eruption this large can pump so much sulfur dioxide gas into the stratosphere that the atmosphere does not have the capacity to oxidize all the SO2 to sulfuric acid aerosol. The atmosphere oxidizes as much SO2 as it can, leaving a huge reservoir of SO2 in the stratosphere. This SO2 gradually reacts to form sulfuric acid as the OH radicals needed for this reaction are gradually produced. The result is a much longer-lasting climate effect than the 1 - 2 years that the magnitude 6 and 7 events of Tambora of 1815 and Pinatubo of 1991 lasted. A magnitude 8 eruption like the Toba event can cool the globe for 6 - 10 years by 3 - 5°C (5 - 9°F), and the controversial Toba Catastrophe Theory asserts that the resulting sudden climate change reduced the Earth's population of humans to 1,000 - 10,000 breeding pairs, creating a "genetic bottleneck".

Figure 4. The 100x30 square kilometer Toba Caldera is situated in north-central Sumatra around 200 km north of the Equator. It is comprised of four overlapping calderas aligned with the Sumatran volcanic chain. Repeated volcanic cataclysms culminated in the stupendous expulsion of the Younger Toba Tuff around 74,000 years ago. The lake area is 100 square kilometers. Samosir Island formed as a result of subsequent uplift above the evacuated magma reservoir. Such resurgent domes are typically seen as the concluding phase of a large eruption. Landsat Enhanced Thematic Mapper Plus (ETM+) browse images for path/row 128/58 (6 September 1999) and 129/58 (21 January 2001) from Copyright USGS. Image source: Oppenheimer, C., 2002, "Limited global change due to the largest known Quaternary eruption, Toba 74 kyr BP?"Quaternary Science Reviews, 21, Issues 14-15, August 2002, Pages 1593-1609.

When can we expect the next magnitude 8 eruption?
Given the observed frequency of one mega-colossal magnitude 8 volcanic eruption every 1.4 million years, the odds of another hitting in the next 100 years is about .014%, according to Mason et al., 2004. This works out to a 1% chance over the next 7200 years. Rampino (2002) puts the average frequency of such eruptions at once every 50,000 years--about double the frequency with which 1-km diameter comets or asteroids capable of causing a similar climatic effect hit the Earth. A likely location for the next mega-colossal eruption would be at the Yellowstone Caldera in Wyoming, which has had magnitude 7 or 8 eruptions as often as every 650,000 years. The last mega-colossal eruption there was about 640,000 years ago. But don't worry, the USGS states that "the Yellowstone volcanic system shows no signs that it is headed toward such an eruption. The probability of a large caldera-forming eruption within the next few thousand years is exceedingly low".

What would happen if a magnitude 8 mega-colossal eruption were to occur today?
If a mega-colossal eruption were to occur today, it would probably not be able to push Earth into an ice age, according to a modeling study done by Jones et al. (2005). They found that an eruption like Toba would cool the Earth by about 17°F (9.4°C) after the first year (Figure 5), and the temperature would gradually recover to 3°F (1.8°C) below normal ten years after the eruption. They found that the eruption would reduce rainfall by 50% globally for the first two years, and up to 90% over the Amazon, Southeast Asia, and central Africa. This would obviously be very bad for human civilization, with the cold and lack of sunshine causing widespread crop failures and starvation of millions of people. Furthermore, the eruption would lead to a partial loss of Earth's protective ozone layer, allowing highly damaging levels of ultraviolet light to penetrate to the surface.

Not even a mega-colossal eruption of this magnitude would stop global warming, though. The level of greenhouse gases in the atmosphere would not be affected by the volcanic eruption, and warming would resume where it left off once the stratospheric dust settled out in a decade. With civilization crippled by the disaster, greenhouse gas emissions would be substantially reduced, though (small solace!) If we really want to say goodbye to civilization, a repeat of the only magnitude 9 eruption in recorded history should do the trick--the magnitude 9.2 La Garita, Colorado blast of 27.8 million years ago (Mason et al., 2004).

Figure 5. Annual near-surface temperature anomalies for the year following a mega-colossal volcanic eruption like the Toba eruption of 74,000 years ago, if it were to occur today. Most land areas cool by 22°F (12°C) compared to average. Some areas, like Africa, cool by 29°F (16°C). Image credit: Jones, G.S., et al., 2005, "An AOGCM simulation of the climate response to a volcanic super-eruption", Climate Dynamics, 25, Numbers 7-8, pp 725-738, December, 2005.

What would happen if a magnitude 7 super-colossal eruption were to occur today?
An eruption today like the magnitude 7 Tambora eruption of 1815 would cause cause isolated regional crop failures for 1 - 2 years after the eruption. With food supplies in the world already stretched thin by rising population, decreased water availability, and conversion of cropland to grow biofuels, such a volcanic eruption might trigger regional famine, threatening the lives of millions of people and potentially igniting wars over scarce resources. However, society's vulnerability to major volcanic eruptions is less than it was, since the globe has warmed significantly in the past 200 years. The famines from the eruptions of 1600 and 1815 both occurred during the Little Ice Age, when global temperatures were about 1.4°F (0.8°C) cooler than today. Crop failures would not be as wide-spread with today's global temperatures, if a super-colossal eruption were to occur. Fifty years from now, when global temperatures are expected to be at least 1.8°F (1°C) warmer, a magnitude 7 eruption should only be able to cool the climate down to year 2009 levels.

For further information
Tambora: The Eruption That Changed the World, a 2014 book by Gillen D'Arcy Wood, is an excellent read.

Volcanic Winter, my April 2009 post.

Volcanic winter article from wikipedia. has a nice article that goes into the volcano-climate connection in greater detail.

The International Conference on Volcanoes, Climate, and Society is holding a special conference this week in Switzerland, Bicentenary of the great Tambora eruption (thanks go to Mike Chenoweth for alerting me to this.)

Jones, G.S., et al., 2005, "An AOGCM simulation of the climate response to a volcanic super-eruption", Climate Dynamics, 25, Numbers 7-8, pp 725-738, December, 2005.

Mason, B.G., D.M. Pyle, and C. Oppenheimer, 2004, "The size and frequency of the largest observed explosive eruptions on Earth", Bulletin of Volcanology" 66, Number 8, December 2004, pp 735-748.

Verosub, K.L., and J. Lippman, 2008, "Global Impacts of the 1600 Eruption of Peru's Huaynaputina Volcano", EOS 89, 15, 8 April 2008, pp 141-142.

Jeff Masters


Major Severe Weather Outbreak Possible This Week

By: Bob Henson , 4:13 PM GMT on April 06, 2015

The atmospheric ingredients are aligning for what could be intense severe weather this week, especially on Wednesday and Thursday. A powerful upper-level low is expected to bring the storminess to the Plains, Midwest, and South as it slowly makes its way eastward. The low is now pushing into California, where its power is being put to good use: providing much-needed snow in the Sierras and rain at lower elevations. From 4” to 8” of snow was observed above 3500 feet in the Sierra over the weekend, and winter storm warnings are in effect for 8-16” of higher-elevation snow late Monday into Tuesday, with local two-foot amounts possible on the highest peaks. The San Francisco Bay area could get anywhere from 0.5” to 2” of rain. While this won’t come close to breaking the severe multi-year drought across California, it’ll at least add a few drops to the bucket and give residents a psychological boost. The cold upper-level air may even lead to severe thunderstorms over central California on Tuesday, with a tornado or two possible.

Figure 1. Dew points as of 9:00 am CDT Monday, April 6, had already risen above 55°F across Texas and Oklahoma, with 65°F values moving north from the Gulf of Mexico. Higher dew points indicate richer moisture near the surface; most severe weather occurs with dew points of at least 55°F. Image credit: NCAR/RAL Real-Time Weather Data.

Ahead of the upper low, high-level southwesterly winds will overspread much of the country over the next several days. This flow over the Rockies will help maintain surface low pressure over the high plains of Colorado and Kansas, and the circulation will pull in plenty of moisture. As shown in Figure 1 above, dew point temperatures (the temperature to which the air needs to be cooled in order for the relative humidity to reach 100%) are already near 70°F along the Texas coast--not too far from typical summertime values. This rich moisture will surge north through the week, with mild, humid air possibly making it as far north as Chicago and Cleveland by Thursday. The juxtaposition of muggy low-level air and the cold upper-level storm will produce strong instability over a wide area. However, a very warm, dry layer sandwiched between the two—an atmospheric “cap”—should keep storms from becoming widespread on Monday and Tuesday. Any storms that do manage to break through the cap could quickly become severe, especially along a dry line from Texas to Missouri. Late Monday and again late Tuesday, overnight storms could produce severe wind or hail across parts of northeast Kansas and Missouri.

Figure 2. NOAA’s Storm Prediction Center has placed much of the southern Plains in a slight risk of severe weather for this Wednesday, April 8. Image credit: NOAA/SPC.

Computer models are in strong agreement that the situation will become more volatile by Wednesday afternoon, as the upper low pushes into the Great Basin and pieces of energy swing around it onto the Plains. The unusually rich moisture for early April will lead to CAPE values perhaps exceeding 3000 J/kg, which is more than sufficient for supercell thunderstorms. (CAPE is “convective available potential energy,” or the amount of energy that could be unleashed as rising motion if a storm begins to develop.) In addition, the dry line will sharpen and begin moving east, and a warm front will also sharpen east of a surface low in the vicinity of central Kansas. As air converges along the dry line and front, it will be forced upward, encouraging storm development. Another crucial factor will be the strong vertical wind shear, or the variation from low-level southerlies to much stronger southwesterlies just above the surface. Strong wind shear imparts a spin to air parcels, and as they feed into a supercell thunderstorm, their spin (or vorticity) can become stretched and concentrated, enhancing storm rotation and possible tornado formation. (For an excellent depiction of this process, see this National Geographic interactive animation, which illustrates the classic supercellular tornado process. Weaker, shorter-lived tornadoes can form in other ways.)

All of the factors noted above are strongly associated with classic severe weather outbreaks, and their expected intensity is such that significant severe weather is is possible, as mentioned by NOAA’s Storm Prediction Center in its Day 3 outlook for Wednesday, issued early Monday. The area most at risk for tornadic storms (see Figure 2) is along the dry line, anticipated to extend from central Oklahoma into central Kansas, and along the warm front through eastern Kansas. Since the storms may not be exceptionally numerous at first, SPC’s current outlook for Wednesday calls for only a “slight” risk of severe weather, even though tornadic supercells are quite possible where storms do form.

Figure 3. The red zone on this map indicates an elevated risk of supercell thunderstorms at 6 pm Wednesday, based on Monday’s 1200 GMT NAM model run. The supercell composite parameter combines several measures of instability and vertical wind shear. The wind flags show the contrasts in wind speed and direction between the 500 mb (blue) and 850 mb (black) levels. Strong vertical wind shear is evident across much of Oklahoma, southern Kansas, and southwest Missouri, where powerful westerly winds at 500 mb are flowing above more southerly flow at 850 mb. Image credit: College of DuPage NeXT Generation Weather Lab.

The upper low will sweep into the central Plains on Thursday, pushing the risk area for severe storms well eastward. Much will depend on where storms develop on Wednesday night and how much they persist into Thursday morning. Where the air is not extensively rain-cooled, very intense storms could develop along the surging cold front and just east of the surface low, perhaps reaching eastern Iowa, Illinois, and Wisconsin by evening. Upper-level winds will be even stronger than on Wednesday, and any tornadoes that form could be moving rapidly, adding to the threat. By Thursday night, a large complex of severe storms may bring high winds, large hail, and very heavy rain from east Texas into the Tennessee and Ohio valleys. These storms are likely to weaken somewhat as they move further from the upper low into the Gulf and Atlantic coastal states by Friday. The system may also bring additional rain to flood-hammered parts of Kentucky. According to the Weather Channel’s Nick Wiltgen, Louisville, KY, saw its fourth-wettest calendar day on record last Friday, April 3, with 5.64” at Standiford Field (the city’s official reporting site) and 8.03” at the Louisville NWS office. The city has received more than a foot of rain and melted snow since March 1. More than 100 water rescues were carried out in the Louisville area, and Kentucky governor Steve Beshear declared a state of emergency on Saturday.

Weather and climate talks, hands-on science this weekend in Nebraska
I’ll be delivering a talk and signing copies of my book “The Thinking Person’s Guide to Climate Change” this Saturday, April 11, at the Central Plains Severe Weather Symposium and Family Weatherfest in Lincoln, Nebraska. This free event draws several thousand people each year from throughout the state and region. The symposium, organized by University of Nebraska meteorology professor Kenneth Dewey with a variety of sponsors, began in 1999 and features a half-day of speakers from eastern Nebraska and beyond. Representatives from the Nebraska Office of Emergency Management will discuss the state’s response to the disastrous twin tornadoes that struck the town of Pilger last June 16. Joining me for the book signing will be Nancy Gaarder, a top-notch weather reporter at the Omaha World-Herald. Nancy has just released “Nebraska Weather,” a 200-page guide with dozens of photos from the World-Herald archives. The concurrent Family Weatherfest is modeled after a similar event held at the annual meeting of the American Meteorological Society. Local TV weathercasters will be on hand, and kids can deliver forecasts on the same type of “green screens” used by the pros.

Bob Henson

Severe Weather

A Rare Easter Typhoon for the Philippines; Chile Flood Toll: 107 Dead or Missing

By: JeffMasters, 9:27 PM GMT on April 03, 2015

Typhoon Maysak will be a rare and unwelcome Easter visitor this weekend in the Philippines' Luzon Island. The people of the Philippines are used to seeing tropical cyclones, but not during Easter! Only seven tropical storms or typhoons have hit Luzon between January and April since 1945, an average of one such storm every ten years. At 2 pm EDT Friday the Joint Typhoon Warning Center (JTWC) put Maysak's top sustained winds at 90 mph, and the Japan Meteorological Agency (JMA) put Maysak's central pressure at 975 mb. Satellite loops on Friday afternoon showed the storm's heavy thunderstorms have shrunk greatly in areal coverage and intensity since the storm's Category 5 days, and an eye is no longer distinct. Maysak was under moderate wind shear of 10 - 20 knots, and there is some dry air surrounding the storm that will get driven into the core by the wind shear, further weakening the storm before landfall. The Joint Typhoon Warning Center (JTWC) is predicting that Maysak will be a Category 1 typhoon with 75 mph winds when it hits Luzon this weekend, and the main threat from the storm will be heavy rains causing flash floods. The 12 UTC Friday runs of the GFS and European models predicted that the center of Maysak would come ashore in Luzon near 20 UTC (4 pm EDT) Saturday. The 06 UTC Friday run of the GFDL model predicted that Maysak would bring a modest area of 4 - 8" of rain to northern Luzon, which is less than the typical tropical storm brings to the Philippines, and should not result in catastrophic flooding.

Figure 1. Tracks of all tropical storms and typhoons to affect the Philippines' Luzon Island between the months of January - April. Only seven such storms have hit Luzon since 1945, an average of one every ten years. Image credit: NOAA.

Maysak kills 9 in Micronesia
Maysak is responsible for widespread destruction and at least nine deaths in the Federated States of Micronesia. Estimates from The Red Cross suggested that there were at least 5,000 people who were in desperate need of food, water and shelter, and needed emergency assistance. Maysak passed through the Chuuk State of Micronesia over the weekend as a Category 1 typhoon, and Maysak's southern eyewall passed over the sparsely populated islands of Fais and Ulithi in the Yap State of Micronesia while the storm was at Category 5 strength. Most structures on Ulithi not made of concrete were damaged or destroyed by Maysak's powerful winds. The entirety of the island's crop were ruined by the typhoon's storm surge, with early estimates indicating that it would be a full year before crops could be planted again, due to salt water intrusion. Robert Speta has more details on the impacts on Ulithi on his Twitter feed.

Chile flood toll: 107 dead or missing
The death toll in Chile from severe flooding that hit March 23 - 26, 2015, is now 24, with 83 others officially listed as missing. According to EM-DAT, this would rank as Chile's 4th deadliest flood in recorded history. Although rainfall amounts were generally less than 2" (50.8 mm), the rains fell on Northern Chile's Atacama Desert region--the driest place on the planet. Antofagasta, which averaged just 3.8 mm of precipitation per year between 1970 - 2000, and has a long-term average of 1.7 mm of precipitation per year, received a deluge of 24.4 mm (0.96 inches) during the 24 hour period ending at 8 am EDT March 26. That's over fourteen years of rain in one day! According to weather records researcher Maximiliano Herrera, some areas in the Atacama Desert saw the equivalent of a century or so of rain in few hours. The 4 mm of rain that fell on the driest place on Earth--Quillagua, Chile--on March 23 - 25 was the first rain there in 23 years, and the amount that fell was about the same amount that had fallen in the previous fifty years. The rains triggered flooding that damaged some houses in the town. Apparently, the previous rain episode in Quillagua before 2015 was in 1918 or in 1919. All other precipition events were from blowing drizzle.

This is a chronicle of the biggest rainfall events in Antofagasta, Chile with daily amounts above 10 mm over the past century (from Maximiliano Herrera, who maintains a comprehensive set of extreme temperature records on his web site):

18 May 1912: 24 mm
3 July 1925:  16.3 mm
5 July 1927: 12.6 mm
13 July 1928:  13.3 mm
21 August 1930: 26.2mm/27.1mm (2 stations)
30 June 1932:  11.0 mm
13 June 1940:  39.4 mm/38.0 mm (2 stations)
27 July 1987:  22.8 mm
18-19 June 1991: 42.0 mm/17.0 mm (2 stations)

The 1912, 1940 and 1991 rain events all caused floods that had catastrophic consequences in terms of economical and human losses.

Video 1. Incredible flooding in ‪Chanaral, Chile‬, on March 25, 2015. I've seen flood videos of cars, trucks, and houses being washed downstream before, but railroad cars? Yikes! A better version of this video with sound is available on Facebook.

Video 2. Flash flooding in a town near the Chile/Peru border on March 25, 2015.

Chile's heavy rains were due to an unusually strong and persistent "cut-off" low pressure system that was trapped along the coast by an exceptionally strong ridge of high pressure, which also brought about another remarkable weather event--the warmest temperatures ever recorded in Antarctica (63.5°F). A cold front associated with the cut-off low hit the Andes Mountains, dumping rains over soils with very little vegetation (due to the dry climate.) Unusually warm ocean temperatures approximately 1°C (1.8°F) above average off of the coast meant that high amounts of water vapor were available to fuel the storm and generate exceptionally heavy rains. Heavy precipitation events are common in Chile during El Niño events, like we are experiencing now. El Niño brings warmer than average waters to the Pacific coast of South America where Chile lies.

This week’s WunderPoster: Aurora
Last month provided high-latitude
skywatchers with a spectacular example of the aurora, the phenomenon highlighted in this week’s WunderPoster. Commonly referred to as the “northern lights” (aurora borealis) or “southern lights” (aurora australis), these sky shows are a product of electrons spewed from the sun that interact with gases in Earth’s outermost atmosphere, anywhere from about 50 to 300 miles above the surface. Auroral activity is greatly enhanced when gigantic bursts of electromagnetic energy emerge from the sun’s surface during solar storms.

Figure 2. Katy Turk captured this amazing aurora from eastern Alaska last month. Image credit: wunderphotographer katy97780.

Have a great Easter weekend, everyone!

Jeff Masters and Bob Henson

Hurricane Flood

California’s Deepening Drought: Ten Things to Know

By: Bob Henson , 4:54 PM GMT on April 02, 2015

California’s four-year struggle with drought entered an ominous new phase on Wednesday, as the California Department of Water Resources conducted its annual April 1 survey of the crucial Sierra snowpack. Runoff from snowmelt across the Sierra Nevada provides about 30% of the state’s average water supply. Nobody expected good numbers to emerge from the April 1 survey, given the obvious lack of snow across the Sierra, but the report was still a shocker. As the agency put it in its headline, without any need to exaggerate, “Sierra Nevada Snowpack is Virtually Gone.”

Figure 1. A study in high contrast: the Sierra snow survey being conducted at the Phillips course on March 28, 2013 (top) and April 1, 2015, with California governor Jerry Brown addressing reporters (bottom). Image credit: California Department of Water Resources.

As of Wednesday, the snowpack held just 1.4 inches of water--only about 5% of its usual water content for the date, compared to a previous record low of 25% in both 1977 and 2014. At the Phillips snow course (elevation 6800 feet), the ground was completely bare for the first time in 75 years of early-April measurement. In a typical year, that course would be covered by more than five feet of snow. California’s wet season is rapidly drawing to a close, so there’s little hope of any major recovery in the snowpack, which is dwindling fast at a time when it ought to be peaking (see Figure 2).

In a press conference linked to the survey results, California governor Jerry Brown announced the state’s first-ever mandatory water restrictions, including a 25% statewide cut in municipal water use compared to 2013 usage. California is the nation’s most populous state and the world’s eighth-largest economy, so the drought and its implications will be major news for many weeks and months to come. What are some of the key take-away points for now?

•  This winter has not been the driest in California history. Some 40% of California’s precipitation comes in the form of powerful “atmospheric river” storm systems, separated by long dry spells. This year the divide was especially sharp, with a sequence of storms in December and another in February providing the great bulk of this winter’s rain and snow. Across most of the state, these storms were bountiful enough to push precipitation totals for the water year to date (October 1 - March 31) somewhat higher than the values seen over the same period in 2013-14, though still below average. The totals through March 31 were roughly 70 - 90% of average across northern California, 50 - 80% in central CA, and 40 - 60% in the south. San Francisco’s wet December (11.70”) obscures the fact that downtown SF followed up with its driest January-to-March in 156 years of record keeping. As noted by Bay Area consulting meteorologist Jan Null, only 1.59” fell, compared to the previous record of 2.31” set in 2013. (The next driest Jan-Mar was 3.20” in 1851.)

Figure 2. The already-pathetic snowpack in the Sierra Nevada has been dropping just at the time it would be peaking in a typical year. Image credit: California Department of Water Resources.

• This winter has been the warmest in California weather history, by far. On a statewide level, what’s truly historic hasn’t been the lack of precipitation but the extremely mild temperatures. According to NOAA’s National Climatic Data Center, the average temperature for California during meteorological winter (Dec - Feb) of 49.5°F was far above the previous winter record of 47.2°F, set in 1980-81. Most recently, towns and cities across the state shattered records for their warmest March, including Sacramento as well as many reporting stations in the Los Angeles and San Diego areas.

Figure 3. Temperatures averaged well above normal across most of the western U.S. in March. Image credit: Western Regional Climate Center.

• The “snow drought” is truly off the charts. This winter’s extreme mildness meant that much of the usual snowfall over the Sierra Nevada either arrived as rain or melted quickly. Never in its recorded history has the Sierra ended up with so little snow by winter’s end. Most of the ski areas in the Lake Tahoe region were closed by mid-March, weeks ahead of schedule. Some high-elevation rivers and streams will struggle to avoid running completely dry this year.

• Reservoirs are fuller than you might expect--but not for long. Thanks in large part to the unusually sizable fraction of rain vs. snow in the Sierra, reservoirs benefited from generous winter runoff, although most are still well below average (see Figure 4). According to Jan Null, the state’s reservoirs as a whole are now about 5% closer to full capacity than they were on June 30 of last year. Alas, the current numbers should drop more quickly than usual this spring, since there will be very little snowmelt to replenish the reservoirs.

Figure 4. Reservoirs across California (blue levels) were running well below capacity (top of bars) and historical averages (red lines). Blue values below each reservoir show the percent of capacity; red values show the percent of long-term average. Image credit: Western Regional Climate Center.

• High-elevation fires could be ferocious this summer. California’s lower-elevation grassland and shrubland fires tend to be at their worst when a wet year fosters growth that dries out over the following year. It’s a somewhat different picture in the high-elevation forests of the Sierra, where unusually dry, warm conditions in springtime are the main factor setting the stage for summer wildfire. The lack of snowpack and the persistent record heat suggest that a very serious wildfire risk could emerge at higher altitudes this summer. In its spring/summer outlook issued on Wednesday, the National Interagency Fire Center projected above-average wildland fire risk by June and July across western Idaho, southwest Arizona, and most of California, Oregon, and Washington. “The current drought is very likely going to increase the number and severity of fires in the mountains, but will likely reduce fire activity in the foothills due to reduced grass growth,” USGS research scientist and Sierra fire expert Jon Keeley told me in an email.

• Agriculture may face a year of reckoning. Some 80% of California’s developed water supply is used by agriculture, and the recent drought has prompted many growers to pump from groundwater at increasing rates. The state has lagged in forcing public disclosure of groundwater use, so it’s hard to assess how quickly the aquifers are being depleted, but any natural recharge will take many years, and the cost of pumping goes up significantly as the water table goes down. The state’s Mediterranean climate, with its wet, mild winters and dry, warm summers, is ideal for growing a huge array of crops, but some are far more water-thirsty than others, and irrigation techniques (such as flooding an entire field vs. using drip lines) make a huge difference in how much water is needed. This year may force large segments of California agriculture to confront hard choices.

•  Other parts of the Southwest are also contending with serious drought. Unlike California, the Southwest has been in near-continuous drought since 2000, with only modest spells of relief. Nevada’s Lake Mead, which provides water to Las Vegas as well as Los Angeles, continues to be far below capacity, and projections are that the lake level will hit another record low this spring, following a record low last summer. With snowpack across the upper Colorado River basin again less than average, Arizona’s Lake Powell (Figure 5, below) is also expected to remain close to its record lows. The decline in both lakes is prompting serious long-term concern about water and power availability throughout the region.

Figure 5. “Bathtub ring” water lines are visible on March 30, 2015, on a section of Lake Powell formerly under water near Big Water, Utah. Lake Powell is currently at 45 percent of capacity and is projected to recover only slightly this year, ending up near 47 percent of capacity by September. The Colorado River Basin supplies water to 40 million people in seven western states. Image credit: Justin Sullivan/Getty Images.

• Even a strong El Niño may not save the day. For more than a year, Californians have been teased by the off-and-on signals that a major El Niño event could bring a wet year to the state. Computer models are now increasingly emphatic that El Niño conditions will intensify to at least moderate levels by summer, and climatology would favor any such event growing during the fall and winter. But while strong El Niño events do raise the odds of a wet winter substantially, a drier-than-average year is still possible, and weak-to-moderate El Niño events have a much less consistent influence.

•  There’s really no telling how long the drought will last. Paleoclimatology tells us that megadroughts lasting one to several decades--even centuries--have struck California over the last 1200 years. The factors that produce such long-lived drought have yet to be nailed down, although some research has pointed to persistent La Niña-like conditions in the tropical Pacific. Putting wishful thinking aside, policymakers and citizens must grapple with the chance that the current drought could continue for years more. What’s more, the effects of any precipitation downturn are increasingly likely to be exacerbated by above-average temperatures. As we’ll explore in an upcoming post, unusual heat is becoming the norm when California experiences long dry spells, and this raises major concerns about the impacts of future drought in a warming climate.

•  Any winter could still bring catastrophic floods to California. Paradoxical and perverse as it may seem, a warming planet tends to boost both ends of the hydrologic spectrum. Warmer air temperatures enhance evaporation from land, making dry soils even drier, while also increasing evaporation from the oceans, adding moisture to the air and increasing the ability of a given storm to dump rain or snow. When it does rain in California, it can pour--as evidenced by the devastating floods of 1861-62, which inundated much of the Central Valley and put downtown Sacramento under ten feet of water. A similar event today could produce more than $300 billion in economic impacts, according to a 2011 USGS study. New research is digging into the latest round of coordinated climate modeling (CMIP5) and what it reveals about possible changes in California hydrology. Such work is still ongoing, but one study led by Michael Warner (University of Washington), published last February in the Journal of Hydrometeorology, suggests that average winter precipitation along the North American west coast could increase by 11% to 18% by the end of the 21st century. The bump-up appears to be almost completely due to richer atmospheric moisture rather than increased winds. The study indicates that the most extreme days (as measured by vertically integrated water vapor) could see anywhere from 15% to 39% more precipitation. Thus, in a state renowned for extremes of rain and snow, there are signs that the future may hold even more “extreme extremes.”

Many thanks to Jan Null and Weather Underground historian Chris Burt for data and graphics incorporated in this post.

Bob Henson


Space Station Captures Spectacular Images of Typhoon Maysak

By: Jeff Masters , 9:22 PM GMT on April 01, 2015

Category 4 Typhoon Maysak is headed west-northwest towards the Philippines, after pounding the islands of Yap State in Micronesia's Caroline Islands on Tuesday. At 2 pm EDT Wednesday the Joint Typhoon Warning Center (JTWC) put Maysak's top sustained winds at 140 mph, and the Japan Meteorological Agency (JMA) put Maysak's central pressure at 935 mb. Maysak underwent an eyewall replacement cycle early on Wednesday, when the inner eyewall collapsed and was replaced by a larger-diameter eyewall that formed from a spiral band. This process weakened the storm's winds by 20 mph, and satellite loops showed a shrinking of the storm's heavy thunderstorms, along with a warming of the cloud tops. However, on Wednesday afternoon, the cloud tops began cooling and the area of heavy thunderstorms was expanding, showing that Maysak had recovered from its eyewall replacement cycle and might be ready to intensify once again. Maysak has moderate wind shear of 10 - 20 knots and a large area of ocean with sea surface temperatures of 28°C (82°F) to work with until landfall. As Maysak approaches the Philippines, wind shear will rise to the high range (20 - 30 knots), and there is some dry air surrounding the storm that will likely get driven into the core by the high wind shear. The total heat energy in the ocean will decrease, which should also help allow weakening to occur. The Joint Typhoon Warning Center (JTWC) is predicting that Maysak will be a Category 1 storm when it hits Luzon Island in the Philippines. The 12 UTC Wednesday runs of the GFS and European models predicted that the center of Maysak would come ashore in Luzon near 21 UTC (5 pm EDT) Saturday.

Figure 1. Some of the most spectacular images ever captured of a tropical cyclone from space: Category 5 Super Typhoon Maysak as seen from the International Space Station at approximately 6 pm EDT Tuesday March 31, 2015 (just after dawn local time.) At the time, Mayask had top winds of 160 mph as estimated by the Joint Typhoon Warning Center, and a central pressure of 905 mb, as estimated by the Japan Meteorological Agency. I brightened the images and flipped them 180 degrees using Photoshop to better show them off. Image credit: Terry W. Virts.

Maysak was the strongest typhoon (by pressure) so early in the year
At its peak strength on Tuesday, the Japan Meteorological Agency (JMA) put Maysak's central pressure at 905 mb, the lowest pressure they have estimated for any typhoon occurring so early in the year (previous record: 930 mb for Typhoon Mitag of March 2002, Typhoon Alice of January 1979, and Typhoon Harriet of January 1959.) The earliest in any year we've seen a typhoon stronger than Maysak was in 1971, when Super Typhoon Amy deepened to 890 mb on May 2. JTWC gave Maysak a Category 5 rating with 160 mph winds on Tuesday, making it one of only three Category 5 typhoons ever observed in the Northwest Pacific prior to April (the other two were Super Typhoon Ophelia of January 1958 and Super Typhoon Mitag of March 2002, both with 160-mph winds). According to intensity estimates from the Joint Typhoon Warning Center, 2015 is the first year on record to have three Category 5 storms form in the Pacific Ocean during the first three months of the year. The other two Category 5 storms in 2015 were Tropical Cyclone Pam (165 mph winds), which devastated Vanuatu in mid-March, and Tropical Cyclone Eunice (160 mph winds), which affected ocean areas in the South Indian Ocean. Reliable satellite records of Southern Hemisphere tropical cyclones extend back to the early 1990s, so we only have about a 25-year period of good records for global tropical cyclones. Earth averaged 4.6 Category 5 storms per year between 1990 - 2014, with 59% of these occurring in the Northwest Pacific.

Maysak causes heavy damage to Chuuk and Yap
At least 5 deaths and extensive damage have been reported on Chuuk State (Micronesia), where Maysak passed through over the weekend as a Category 1 typhoon. Up to 90% of the homes were reportedly damaged or destroyed by the storm. On Tuesday, Maysak's northern eyewall passed over the sparsely populated islands of Fais and Ulithi in the Yap State of Micronesia while the storm was close to its top strength, and damage was likely severe to catastrophic on those islands. Chuuk and Yap should keep an eye on a new tropical disturbance, Invest 99W, which is organizing near where Maysak formed. The latest 12Z UTC Wednesday runs of the GFS and European models show 99W becoming no worse than a weak tropical storm, though, and the JTWC is giving 99W low odds of developing.

Bob Henson will have a post Thursday on the results of California's crucial April 1 snow survey.

Jeff Masters


Invest 92L Retired From List of Tropical Disturbances

By: JeffMasters, 12:46 PM GMT on April 01, 2015

The World Meteorological Organization (WMO) announced a surprise addition to the list of retired Atlantic storm names during their annual meeting held in Ann Arbor, Michigan yesterday: henceforth, the name "Invest 92L" will no longer be used for tropical disturbances in the Atlantic, after that storm savaged South Florida in September 2014. Damage from Invest 92L as it swept across South Florida on September 11, 2014 was piddly, but as residents of Florida can attest to, the media hype surrounding the approach of the storm was extreme, thanks to computer model projections that showed the storm potentially intensifying into a serious heavy rainfall and wind event. Given the massive media attention given to the storm, the WMO decided that it would be unwise to give future tropical disturbances the same name, to avoid confusion with the September 2014 version of "Invest 92L".

Figure 1. Invest 92L swirls over Florida at 12:30 pm EDT Friday September 12, 2014. Image credit: NASA.

Figure 2. Damage from Invest 92L's rampage across South Florida on September 10, 2014, was mind-numbing, as this photo demonstrates. Image credit: wunderground member Ameister12. Credit also goes to wunderground member MAWeatherboy1 for commenting on this photo in my September 12, 2014 blog post, saying, "It's hard to imagine the scope of the damage in Florida this morning. 92L will probably get retired from the invest list for this."

With the name "Invest 92L" now excluded from the list of tropical disturbance names that NHC can use, they were in the awkward position of having to jump from Invest 91L to Invest 93L, skipping over the name Invest 92L, during this year's hurricane season. In addition, the WMO could decide to retire more "Invest" names in the future, so NHC decided to come up with a radically new system for naming tropical disturbances. NHC director Dr. Rick Blabb announced yesterday that the list of tropical disturbances for 2015 would completely do away with the numbering system used in the past and be replaced by more memorable names. Here, then, is the list of names for Atlantic tropical disturbances in 2015:

Dr. Evil
Ralph the Wunder Llama
Mr. Bill
Little Rascal
HAL 9000
Stay Puft Marshallow Man
Miss Piggy
The Borg
Sponge Bob
Ms. Pac-Man
Bob Dobbs
Mr. Mxyzptlk
Anne of Green Gables

In a press release, Dr. Blabb extolled the virtues of the new system of naming tropical disturbances: "It used to be that we called tropical disturbances "Invests" and numbered them beginning at 90 and ending at 99, and then recycled the name back to 90 after we hit 99. This really doesn't make much sense. I mean, come on, why didn't we give each start a unique number, like 1 through 99? And why do we give each tropical disturbance the letter "L" after it, to denote the "atLantic Ocean?" OK, the letter "A" is reserved for tropical disturbances in the Arabian Sea, but the Atlantic is far more deserving of getting the coveted letter "A" for its tropical disturbances, since we get far more activity than the Arabian Sea. And why do we call them "Invests", like they were code for some sort of obscure financial strategy? Instead of "Invests", we could call them "Tropical Disturbances", but that has the initials "TD", which could get them confused with Tropical Depressions. Calling them "Areas of Interest" is way too boring, so we decided to call them "Thingamabobbers." Numbers aren't very memorable, so it makes much more sense to attach names to our Thingamabobbers. The names we picked this year are not fixed in a certain order, so we can assign a name when a Thingamabobber gets designated, based on what we expect the storm's character to be. For example, if we expect a Thingamabobber to make many course changes we might name it "Thingamabobber Pac-Man" or "Thingamabobber Ms. Pac-Man." A storm with a lot of electrical activity we might call Pikachu, and a fast-moving storm might be called Zippy. A Thingamabobber that has the strong potential to become a nasty hurricane would get a name like Sauron, Bellatrix, or Cruella, and a relatively innocuous one might get named Little Rascal, Pipsqueak, or Sponge Bob. Although we might get some criticism for our choice of names, it sure makes a lot more sense than the ridiculous Invest 90L through 99L naming scheme that we use now."

Happy April Fool's Day!

Jeff Masters

Humor Hurricane

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Category 6™


Cat 6 lead authors: WU cofounder Dr. Jeff Masters (right), who flew w/NOAA Hurricane Hunters 1986-1990, & WU meteorologist Bob Henson, @bhensonweather