Category 6™

Looking Ahead to 2017: What to Watch For, Weather- and Climate-Wise

By: Bob Henson , 1:51 PM GMT on December 30, 2016

Between a record-strong El Niño and catastrophic floods, fires, and drought, 2016 was a memorable year for weather and climate in North America as well as globally. What can we expect as we roll into 2017? A precise weather forecast is asking too much, but there is already a lot we can say about some key factors. Here are six developments to watch for in 2017. They’re presented in rough order of increasing confidence, followed by details on each prediction.

1. Better odds of El Niño than La Niña, but a neutral Pacific still favored
2. Wide range of possibilities for Atlantic hurricane action
3. More tornadoes and tornado deaths in 2017 than 2016? Probably so
4. A very warm year globally, but likely short of a record
5. Another new peak in global carbon dioxide
6. Slam dunk: a spectacular total eclipse in August


1. Better odds of El Niño than La Niña, but a neutral Pacific still favored
The biggest single driver of year-to-year atmospheric variations around the globe is the El Niño–Southern Oscillation (ENSO), including El Niño and its counterpart, La Niña. A year ago, it was virtually certain that the record-strong El Niño of 2015-16 would continue through at least the first few months of 2016, as it indeed did. This time around, the ENSO signal is far less clear-cut. Sea surface temperatures (SSTs) in the benchmark Niño3.4 region of the eastern tropical Pacific have been inconclusive in recent months, hovering close to the La Niña threshold (at least -0.5°C below the seasonal average) since late July.


Figure 1. Departures from average sea surface temperature for this time of year as of mid-December show a diffuse, borderline La Niña signal across the central and eastern tropical Pacific. Image credit: NOAA Climate Prediction Center.

It’s now become less likely that the ocean and atmosphere will commit to a well-defined La Niña event for early 2017. There’s almost no telling what will happen later in the year, on the other side of the infamous “spring predictability barrier” that often separates one El Niño or La Niña event from another. One clue we do have is the unusual persistence this year of a belt of warmer-than-average SSTs from the central tropical Pacific to the west coast of North America. This warm phase of what’s called the Pacific Meridional Mode may herald a new El Niño event in 2017-18, as niftily explained by Dan Vimont (University of Wisconsin Center for Climatic Research) in a recent climate.gov post.

In their joint probabilistic outlook issued in early December, NOAA’s Climate Prediction Center (CPC) and the International Research Institute for Climate and Society (IRI) called for decreasing odds of La Niña over the next few months, dropping to just 18% by late spring. Neutral conditions are deemed most likely by CPC/IRI, with 65% odds by spring and 53% by summer. And the odds of El Niño are expected to steadily rise throughout the first half of 2017, reaching 29% by summer. Strong El Niño events like the one we just had are usually followed by a significant La Niña event. If the atmosphere instead ends up cueing El Niño for 2017-18, it would reinforce the notion that we’ve entered a positive phase of the Pacific Decadal Oscillation--a sign that we might expect more El Niño than La Niña events for as long as a decade or two.


Figure 2. Probabilities of El Niño (red), La Niña (blue), and neutral conditions (green), for each overlapping three-month period from November-January 2016-17 (left) to July-September 2017 (right). These probabilities are set each month by forecasters from NOAA’s Climate Prediction Center and the International Research Institute for Climate and Society. Image credit: NOAA/IRI.

2. Wide range of possibilities for Atlantic hurricane action
The well-predicted demise of the 2015-16 El Niño boosted confidence in 2016’s largely successful seasonal hurricane outlooks for the Atlantic, where wind shear was down from 2015 and sea-surface temperatures saw a spike atop their long-term warming trend. (See our roundup post from December 27 on global tropical cyclones in 2016 and their connections to climate change.) Because ENSO is one of the biggest shapers of Atlantic hurricane seasons, our current uncertainty about next year’s ENSO state means we can’t say much yet about whether the 2017 Atlantic tropical season will be hectic, sedate, or somewhere in between.

Forecasters at Colorado State University no longer issue formal seasonal hurricane outlooks as early as December, but CSU’s Dr. Phil Klotzbach laid out his thoughts for us last week in a qualitative discussion. Along with monitoring ENSO, Klotzbach also keeps close tabs on the Atlantic Multidecadal Oscillation and Atlantic thermohaline circulation, which are cyclic natural variations in SST, surface air pressure, and oceanic flow across the North Atlantic. When the AMO is positive (warm) and the THC is strong, the Atlantic pumps out more hurricanes over periods that can range from 25 to 35 years. At other times, unusually cold waters prevail in the far North Atlantic, typically a sign of a slowdown of the THC and a ramp-down in Atlantic hurricane action.


Figure 3. Warmer-than-average waters covered most of the Atlantic Ocean from the equator northward for the period December 1 - 18, 2016. Image credit: NOAA/ESRL Physical Sciences Division, courtesy Phil Klotzbach.

With cold waters widespread across the far north Atlantic in 2014 and 2015, Klotzbach hypothesized in a 2015 Science article that the active Atlantic period that began in 1995 may have already drawn to a close. Now he’s not so sure. “I was generally thinking we had moved into a cold AMO, but we haven't yet seen the re-emergence of the cold anomalies in the far North Atlantic like we have the past couple of winters (at least not yet!),” Klotzbach told me in an email. For this analysis, Klotzbach typically uses SSTs across a box roughly bounded by 50°N-60°N latitude and 10°W-50°W longitude. Figure 3 shows that only part of this area currently has below-average SSTs. “We're just now moving into the height of winter, though, so we may still see some reemergence and anomalous cooling in the far North Atlantic this winter,” said Klotzbach. “I decided to hedge with the outlook so far, and hopefully we'll have a better idea of what is coming up by the time the April forecast rolls around.” Here are the five possibilities (with odds) put forth by Klotzbach in his December update:

40% chance: AMO/THC is above average and no El Niño occurs (resulting in a seasonal average Accumulated Cyclone Energy (ACE) activity of ~ 130)
20% chance: AMO/THC becomes very strong in 2017 and no El Niño occurs (ACE ~ 170)
20% chance: AMO/THC is below average and no El Niño occurs (ACE ~ 80)
10% chance: AMO/THC is above average and El Niño occurs (ACE ~ 80)
10% chance: AMO/THC is below average and El Niño develops (ACE ~ 50)

3. More tornadoes and tornado deaths in 2017 than 2016? Probably so
It’s been a blessedly quiet year for U.S. tornadoes, climatologically speaking. According to Patrick Marsh (NOAA Storm Prediction Center), the year 2016 delivered a preliminary total of 1060 tornado reports through December 28, with few or none expected through the rest of the year. This may sound like a very high total, but the number of final tornado reports typically drops from the preliminary total by about 15% after duplicate reports have been weeded out. The annual number drops even further relative to prior years when it's adjusted for “inflation” against earlier decades, when fewer people were watching and reporting every twister. Using a linear trend adjustment, Marsh estimates that the final, inflation-adjusted tornado total for 2016 will be around 888, which would be the lowest for any year going back to at least 1954 assuming that the database is normalized (inflation-adjusted) through 2015. "Four of the last five years--2016, 2014, 2013, and 2012--have been the quietest years on record when report inflation is accounted for," says Marsh.

This year did produce a few dramatic outbreaks during peak tornado season, but these played out mostly in open country, where few structures were damaged and few people were hurt. The deadliest events of 2016 were “off-season”: seven people died in a Southeast and East Coast tornado outbreak on February 23-24--the nation’s second-largest February outbreak on record--and five deaths occurred across the South during an overnight outbreak on November 29-30.


Figure 4. Lightning lights up the night sky behind a home in Waverly, Va, that was hit by a tornado earlier in the day, Wednesday, Feb. 24, 2016. Image credit: Todd Spencer/ The Virginian-Pilot via AP.

All told, tornadoes have killed only 17 people in the United States in 2016, well below the average toll of 46 per year over the three prior years. Assuming we make it to December 31 without any additional tornado deaths, which looks almost certain, we’ll have been graced with the least-deadly U.S. year for twisters since 1986, when only 15 people were killed. In data going back to 1875 provided by Harold Brooks (National Severe Storms Laboratory), the only other year with fewer than 20 deaths was 1910, with just 12 fatalities.


Figure 5. During El Niño events (top), the frequency of U.S. tornadoes typically drops. When a La Niña phase prevails (bottom), tornado frequency goes up (indicated by red areas). The effect is strongest in the boxed area. Image credit: From Allen et al., “Influence of the El Niño/Southern Oscillation on tornado and hail frequency in the United States,” Nature Geoscience 2015, courtesy IRI.

The strong El Niño of 2015-16 likely helped tamp down tornado activity this year, at least in the heart of Tornado Alley. Researchers at IRI/Columbia University have shown that the most active spring seasons for tornado and hail over the central U.S., especially the Southern Plains, are linked to strong La Niña events, while the very quietest seasons are related to strong El Niño events. In January 2015, the researchers, led by John Allen (now at Central Michigan University), called for better-than-even odds (54%) of a below-average number of tornadoes this year, as opposed to the 33/33/33% split (below, above, and near average) one would otherwise expect. (See more details at this conference presentation.)

As with Atlantic hurricanes, even a mostly quiet season can still produce deadly mayhem if one destructive event, such as a major landfalling hurricane or a family of violent tornadoes, happens to hit the wrong place at the wrong time. “It’s an ongoing challenge to think about how to convey this information,” Allen told me. “I think it’s also worth noting that we still don't have a lot of other climate signals for improving our forecasts when we don't have ENSO-driven predictability.” It’s thus hard to tell how tornado counts will evolve in 2017, since the ENSO signal is so weak. However, given the very low activity this year, there’s a good chance that we will see more twisters prowling the nation in 2017 than we did in 2016.


Figure 6. The U.K. Met Office predicts that the 2017 global temperature (forecast range shown in green at right) will likely fall below the record value expected to be set in 2016. The dark line shows global temperature since 1850 as calculated by an average of analyses by the Met Office/Hadley Centre, NASA, and NOAA. Each of the three agencies uses slightly different techniques to account for sparsely populated regions, such as the poles. These differences have very little effect on the year-to-year trends, which are in very close agreement for all three analyses. The shaded band shows the 95% uncertainty range for each annual data point. Image credit: U.K. Met Office.

4. A very warm year globally, but likely short of a record
Barring a major, sun-blocking volcanic eruption, we can expect 2017 to continue the long-term warming trend of the last few decades attributed to human-produced greenhouse gases. However, 2017 is unlikely to continue the string of global record highs set in 2014, 2015, and (virtually certainly) 2016. The record-strong El Niño of 2015-16, which sent vast amounts of heat from ocean to atmosphere, played a key role in pushing temperatures just enough above the long-term warming trend to set new global highs. Now that this major El Niño is gone, it’s no surprise that global atmospheric heat is already subsiding a bit relative to seasonal norms--though it would be a huge mistake to interpret this totally expected dip as any sign that longer-term warming has gone away.

On December 20, the U.K. Met Office released its official outlook for 2017 (see Figure 6). The agency projects that global temperature will end up between 0.63 and 0.87°C (1.45 – 1.89°F) above the 1961-1990 average of 14.0°C (57.2°F). “This forecast, which uses the new Met Office supercomputer, adds weight to our earlier prediction that 2017 will be very warm globally but is unlikely to exceed 2015 and 2016: the two warmest years on record since 1850,” said Adam Scaife, head of long-range prediction at the Met Office. According to research fellow Chris Folland: “2016 was well forecast as the methods used detected the warming influence of the strong El Niño. However, last year's El Niño only accounts for around 0.2°C of the global mean temperature rise for 2016, when compared with the long-term average between 1961 and 1990. Increasing greenhouse gases are the main cause of warming since pre-industrial times.”


Figure 7. Carbon dioxide concentration (parts per million in the atmosphere) as measured atop Mauna Loa, Hawaii, in 2015 and 2016. Along with daily, weekly, and monthly variability, there is a reliable yearly cycle associated with the growth and decay of vegetation in the Northern Hemisphere (where most of Earth’s land is located), as well as a steady long-term rise in concentrations due to fossil fuel burning. Image credit: keelingcurve.com, Scripps Institution of Oceanography.

5. Another new peak in global carbon dioxide
Sadly, our highest-confidence forecast for the atmosphere is that carbon dioxide concentrations will continue their relentless upward march. The burning of fossil fuels continues to release more than 35 billion metric tons of CO2, an invisible greenhouse gas, every year. (That’s about 10,300 pounds for every person on Earth.) Just over half of that total is absorbed by plants, soil, and the sea each year. The rest stays in the atmosphere, much of it destined to stay there for many hundreds and even thousands of years.

CO2 values measured atop Mauna Loa Observatory in Hawaii are once again rising toward the usual spring peak after hitting their annual low in late September of around 401 parts per million. Because most of Earth’s plant life is north of the equator, atmospheric CO2 drops with the growth of CO2-absorbing vegetation in late northern spring and summer, and it increases again each winter and spring as vegetation dies off. We can expect daily and weekly CO2 values in spring 2017 to soar above 410 ppm for the first time in human history, and it’s even possible the monthly average will hit that mark as well.

The final weekly value below 400 ppm that we’ll see in our lives is virtually certain to be the 399.86 ppm value recorded in late August 2015 during the approach of Hurricane Madeline. As that hurricane approached Hawaii from the east, its circulation is believed to have imported slightly lower-CO2 air from north of Hawaii.


Figure 8. A total solar eclipse will occur along the belt shown here on August 21, 2017. All of North America and parts of South America will experience at least a partial solar eclipse. Image credit: Fred Espenak (NASA/GSFC), MrEclipse.com

6. Slam-dunk forecast: a spectacular total eclipse in August
We can say with rock-solid confidence that a large swath of the United States will be treated to one of the most widely viewable total solar eclipses in U.S. history (if the weather cooperates!) on August 21, 2017. The band of totality--the region where the sun will be completely obscured by the moon for as long as 2 minutes and 40 seconds--will extend from northern Oregon across the central Plains and mid-South to South Carolina (see Figure 8). Millions of Americans will be within an hour or two’s drive of the totality band, and untold numbers of people from across the world are heading to the States for the big show. The timing of totality will range from about 10 AM PDT on the West Coast to around 2:45 PM EDT on the East Coast. This means that the mid-August sun will be quite high in the sky for the eclipse, enhancing the potential drama.

NASA has a plethora of great material on the upcoming eclipse, including an excellent “Eclipse 101” page with crucial safety tips (for example, never look at an uneclipsed or partially eclipsed sun without specially designed glasses that meet international standards for eclipse viewing). Obviously, there’s no telling what the weather will be doing on August 21, but the perfectly named Eclipseophile website has state-by-state breakdowns of where climatology leans toward the best views. As one might expect, the highest odds of cloud-free skies and dry air are toward the western United States.


Figure 9. Children use protective glasses to look into the sky during a partial solar eclipse outside the Planetario in Madrid, Spain, on the morning of March 20, 2015. The moon covered up to 65 percent of the sun. Image credit: Pablo Blazquez Dominguez/Getty Images.


Figure 10. This photo montage shows the moon passing in front of the sun (top left to bottom right) during a total solar eclipse in the city of Ternate, in Indonesia's Maluku Islands, on March 9, 2016. The total eclipse swept across the Indonesian archipelago on March 9, witnessed by tens of thousands of skygazers and marked by parties, Muslim prayers, and tribal rituals. Image credit: Bay Ismoyo/AFP/Getty Images.

Bob Henson

El Niño

Top Ten Tropical Cyclone Events of 2016 Potentially Influenced by Climate Change

By: Jeff Masters , 4:19 PM GMT on December 27, 2016

Tropical cyclones—which include all hurricanes, typhoons, tropical storms and tropical depressions—are expected to change in intensity, frequency, location, and seasonality as a result of climate change. Many of the tropical cyclones of 2016 exhibited the type of behavior we expect to see more of due to global warming. Here, then, is a “top ten” list of 2016 tropical cyclone events of the type we should expect to see more of due to global warming.

Examples of the strongest storms getting stronger
Tropical cyclones are heat engines which extract heat energy from the oceans and convert it to the kinetic energy of the storms' winds. Thus, the strongest tropical cyclones are expected to get stronger in a world with warmer oceans. It was not a surprise that in 2016—a year with the warmest ocean temperatures on record, globally—we saw the strongest storms ever observed in the two of the six ocean basins that tropical cyclones commonly occur in. If we include the Northern Hemisphere’s strongest tropical cyclone on record—Hurricane Patrica of October 2015—records have been set in three of the six ocean basins over the past two years. The two all-time record storms in 2016 were Tropical Cyclone Winston in the South Pacific (180 mph winds, tied for strongest Southern Hemisphere storm on record) and Tropical Cyclone Fantala in the South Indian Ocean (175 mph winds.) With the upgrade of Super Typhoon Nock-Ten in post-analysis to Category 5 strength, 2016 also saw eight Category 5 storms, which was the fifth greatest on record (since 1990.)


Figure 1. Global Category 5 tropical cyclones from 1990 - 2016, as rated by NOAA's National Hurricane Center and the U.S. Navy's Joint Typhoon Warning Center. This time series is too short to make definitive conclusions about how climate change may be affecting these storms, though the past three years have had the highest 3-year total of Category 5 storms on record. The eight Category 5 storms of 2016 was the fifth highest yearly total on record.

Two of the Top Five Landfalling Tropical Cyclones Occurred in 2016
In addition, 2016 also saw two of the top five strongest landfalling tropical cyclones ever recorded—Super Typhoon Meranti with 190 mph winds on the Philippines’ Itbayat Island (tied for Earth’s strongest landfall on record), and Tropical Cyclone Winston with 180 mph winds at landfall in Fiji (the 5th strongest tropical cyclone at landfall in recorded history.) As we blogged about in August, landfalling typhoons have become more intense since late 1970s, with the peak winds of typhoons striking the region increasing by 12 - 15% since 1977. “The projected ocean surface warming pattern under increasing greenhouse gas forcing suggests that typhoons striking eastern mainland China, Taiwan, Korea and Japan will intensify further,” wrote the authors of the study we blogged about. “Given disproportionate damages by intense typhoons, this represents a heightened threat to people and properties in the region.”


Figure 2. The most intense world tropical cyclones at landfall, using the advisories taken from the National Hurricane Center in the Atlantic and Eastern Pacific, and the Joint Typhoon Warning Center (JTWC) for the rest of the world's oceans. Both agencies use 1-minute averaging times for their advisories, as opposed to the 10-minute averaging time used to report wind speeds by most international weather agencies and at most international airports. Two of the top five strongest landfalling tropical cyclones ever recorded occurred in 2016: Super Typhoon Meranti and Tropical Cyclone Winston. (Note that Super Typhoon Haiyan was originally assessed to have 195 mph winds at landfall by JTWC, but these were reduced to 190 mph after a post-season reanalysis. Also, Hurricane Camille's winds at landfall have also been reduced in a recent reanalysis, from 190 mph to 175 mph, as were Tropical Cyclone Winston’s winds, from 185 mph to 180 mph.)

February 20: Cyclone Winston Ties for Southern Hemisphere’s Strongest Tropical Cyclone on Record (180 mph Winds)
Just four months after the Northern Hemisphere experienced its strongest tropical cyclone on record—Hurricane Patrica of October 2015, with peak winds of 215 mph off the Pacific coast of Mexico—the Southern Hemisphere answered the challenge by spawning its strongest tropical cyclone ever recorded: Tropical Cyclone Winston, which topped out with 180 mph sustained winds at its peak intensity at 06 UTC February 20. These winds are tied for the highest for any Southern Hemisphere tropical cyclone ever rated by the Joint Typhoon Warning Center (JTWC), along with Cyclone Zoe of 2002 and Cyclone Monica of 2006. Winston's lowest central pressure as estimated by the Fiji Meteorological Service was 915 mb at 06 UTC February 20. This ranks Winston as the 29th most intense tropical cyclone in the Southern Hemisphere by pressure (the record lowest pressure is 890 mb by Cyclone Zoe of 2002.) Winston's top winds were higher than its central pressure might imply because it was a relatively small cyclone, so the wind-generating difference in pressure was packed into a small area. Winston’s landfall on Koro Island in Fiji with 180 mph winds puts Winston in fifth place for Earth's strongest landfalling tropical cyclone on record. Winston killed 44 people in Fiji and did $1.4 billion in damage (32% of Fiji's GDP), making it Fiji’s deadliest and most expensive cyclone in recorded history. Winston’s intensity was aided by ocean temperatures that were more than 1°C (1.8°F) warmer than average.


Figure 3. VIIRS infrared image of Tropical Cyclone Winston at 0057 UTC February 20, 2016. At the time, Winston was the strongest storm ever recorded in the Southern Hemisphere, with sustained winds of 180 mph. Fiji’s Koro Island is in the eye. Image credit: NOAA/NESDIS.

April 18: Fantala Ties for Strongest Tropical Cyclone on Record for the Indian Ocean
Tropical Cyclone Fantala intensified to a Category 5 storm with 175 mph winds (as estimated by the Joint Typhoon Warning Center) north of Madagascar on April 18, 2016, making the cyclone as strong as any on record anywhere in the Indian Ocean. Fantala is tied with Tropical Cyclone Agnielle as the strongest cyclone ever observed in the Southwest Indian Ocean. Fantala and Agnielle both top the record holder for the North Indian Ocean (Super Cyclonic Storm Gonu, June 2007, peak 1-minute winds of 165 mph). Reliable satellite-based records for the Indian Ocean only go back to 1990. Note that some consider Tropical Cyclone Monica (180 mph winds) as the strongest Indian Basin storm. Definitions vary on the boundary of the Indian Ocean, though, and Monica reached peak strength north of Australia in the Arafura Sea, which is considered by several sources, including the CIA World Factbook, to be part of the western Pacific Ocean, not the Indian Ocean. Fantala did $4.5 million in damage to Agaléga, Seychelles, Madagascar and Tanzania, and killed thirteen people in Tanzania. Fantala’s intensity was aided by ocean temperatures that were more than 1°C (1.8°F) warmer than average.


Figure 4. A visible image of Tropical Cyclone Fantala collected at 1025Z (6:25 am EDT) on April 18, 2016, by the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor on board the Aqua satellite. The north tip of Madagascar can be seen at bottom. At the time, Fantala was the strongest tropical cyclone ever observed in the Indian Ocean, with winds estimated at 175 mph. Image credit: NASA.

September 13: Super Typhoon Meranti Ties for Strongest Tropical Cyclone on Record at Landfall (190 mph Winds)
Super Typhoon Meranti made a direct hit on the Philippines’ Itbayat Island on September 13, 2016 as a Category 5 storm with 190 mph winds, tying the storm with Super Typhoon Haiyan (2013) for strongest tropical cyclone at landfall in world recorded history. Meranti’s peak 190 mph winds tied it for tenth strongest tropical cyclone in world history (by 1-minute averaged wind speed), according to the “best-track” data from the Joint Typhoon Warning Center and the National Hurricane Center. In addition, Meranti's 890 mb central pressure made it the seventeenth strongest tropical cyclone on record, by pressure. Meranti’s intensity was aided by ocean temperatures that were more than 1°C (1.8°F) warmer than average.

Officially, here are the top-ten strongest tropical cyclones in world history as rated by NOAA's National Hurricane Center and the U.S. Navy's Joint Typhoon Warning Center, by maximum sustained winds:

1) Hurricane Patricia (2015), 215 mph winds (the only Eastern Pacific storm on this list)
2) Super Typhoon Nancy (1961), 215 mph winds, 882 mb. Made landfall as a Cat 2 in Japan, killing 191 people.
3) Super Typhoon Violet (1961), 205 mph winds, 886 mb pressure. Made landfall in Japan as a tropical storm, killing 2 people.
4) Super Typhoon Ida (1958), 200 mph winds, 877 mb pressure. Made landfall as a Cat 1 in Japan, killing 1269 people.
5) Super Typhoon Haiyan (2013), 195 mph winds, 895 mb pressure. Made landfall in the Philippines with 190 mph winds.
5) Super Typhoon Kit (1966), 195 mph winds, 880 mb. Did not make landfall.
5) Super Typhoon Sally (1964), 195 mph winds, 895 mb. Made landfall as a Cat 4 in the Philippines.
5) Super Typhoon Opal (1964), 195 mph winds
5) Super Typhoon Joan (1959), 195 mph winds
10) Super Typhoon Meranti (2016), 190 mph winds, 890 mb pressure.
10) Super Typhoon Tip (1979), 190 mph winds
10) Super Typhoon Vera (1959), 190 mph winds
10) Super Typhoon Louise/Marge (1964), 190 mph winds
10) Hurricane Allen (1980), 190 mph winds (the only Atlantic storm on this list)

However, it is now recognized (Black 1992) that the maximum sustained winds estimated for typhoons during the 1940s to 1960s were too strong, which would make Meranti of 2016 the third strongest reliably measured tropical cyclone in recorded history for the planet.


Figure 5. At 17:32 UTC September 13, 2016, the eye of Super Typhoon Meranti lay directly over the Philippines’ Itbayat Island, as seen in this infrared VIIRS image. Itbayat recorded sustained winds of 112 mph (10-minute average) and a pressure of 934 mb at 1 am local time, 32 minutes prior to this image. At the time, Meranti was a Category 5 storm with 190 mph winds and a central pressure of 890 mb, and was tied for strongest tropical cyclone at landfall in world recorded history.

Examples of a longer tropical cyclone season in 2016
We might expect tropical cyclone seasons to get longer in the future, due to warming ocean temperatures. The Atlantic hurricane season does appear to be getting longer in the Atlantic south of 30°N and east of 75°W, according to a 2008 paper by Dr. James Kossin of the University of Wisconsin. A 2016 analysis by Dr. Ryan Truchelut of WeatherTiger also supported this idea. However, Juliana Karloski and Clark Evans of the University of Wisconsin-Milwaukee found no trend in tropical cyclone formation dates when looking at the entire Atlantic, for the period 1979–2014. A 2015 study of season length in climate models led by MIT’s John Dwyer yielded mixed results, depending upon which model was used to simulate hurricane activity. Regardless, 2016 had four very notable out-of-season storms, probably influenced by unusually warm ocean temperatures: Hurricane Pali in the Central Pacific in January, Hurricane Alex in the Atlantic in January, Hurricane Otto in the Atlantic on Thanksgiving Day and Super Typhoon Nock-Ten in the Philippines on Christmas Day.

January 11: Hurricane Pali: Earliest Eastern Pacific Hurricane on Record
Peaking at Category 2 strength during its eight-day life, Pali was the earliest tropical storm and earliest hurricane ever observed between the International Date Line and the Americas. Only two other tropical cyclones have been observed in January in the Central Pacific. Pali’s formation was aided by ocean temperatures that were more than 2°C (3.6°F) warmer than average. One might consider January storms to "belong" to the previous year's season from a physical point of view.


Figure 6. MODIS visible satellite image of Hurricane Pali taken on the afternoon of January 12, 2016. At the time, Pali was at peak strength--a Category 2 storm with 100 mph winds. Image credit: NASA.

January 14: Alex Becomes the Atlantic’s First January Hurricane Since 1955
On January 14, Hurricane Alex became the Atlantic’s first January hurricane since 1955. Alex maintained Category 1 strength for almost 24 hours, peaking at 85 mph winds, before weakening to a tropical storm with 65 mph winds and making landfall on January 15 on the island of Terceira in the central Azores, roughly 1000 miles west of Portugal. No major damage or casualties were reported from Alex’s landfall. Only one other January storm since records began in 1851 has made landfall in the Atlantic: Hurricane Alice,  which moved from northeast to southwest over the islands of Saint Martin and Saba on January 2, 1954. The only other January hurricane in the Atlantic was Hurricane One on January 4, 1938. Alex’s ascension to hurricane strength was likely aided by sea surface temperatures that were up to 1°C above average for that time of year—near 22°C (72°F.) These unusually warm waters were part of a huge swath of above-average readings that covered much of the globe, strongly suggesting a link to longer-term climate change. On January 13, both Alex in the Atlantic and Pali in the Pacific were active, making it the first time in recorded history to have simultaneous January named storms in both the Atlantic and Pacific.


Figure 7. MODIS visible satellite image of Tropical Storm Alex at 9:20 am EST January 15, 2016. About an hour earlier, Alex’s western eywall passed over the Azores island of Terceira (black outline below the center of Alex). Image credit: NASA.

November 24: Hurricane Otto, Strongest Atlantic Hurricane so Late in the Year
We expect landfalling hurricanes on U.S. holidays like Labor Day (in September), on Independence Day (July 4), and even on occasion Memorial Day (in May.) But on Thanksgiving Day? That was unheard of until 2016, when deadly Hurricane Otto, the first hurricane known to make landfall on Thanksgiving Day, hit Nicaragua as a Category 2 storm with 110 mph winds on November 24. Otto was the Atlantic’s strongest hurricane on record so late in the year, and was the first hurricane to pass directly over Costa Rica since records began in 1851. Otto killed 17 people, making it the third latest deadly tropical cyclone in Atlantic recorded history. (The only later ones: Tropical Storm Olga, which killed 40 people in the Dominican Republic after landfall on December 11, 2007, and Tropical Storm Odette, which killed eight people in the Dominican Republic after landfall on December 6, 2003.) Otto’s formation was aided by ocean temperatures that were up to 1°C (1.8°F) warmer than average.


Figure 8. MODIS satellite image of Otto taken at approximately 11 am EST, November 24, 2016--Thanksgiving Day. At the time, Otto was a Category 2 storm with 110 mph winds about to make landfall in Nicaragua as the strongest Atlantic hurricane ever observed so late in the year. Image credit: NASA.

December 25: Super Typhoon Nock-Ten, Strongest Landfalling Northwest Pacific Typhoon so Late in the Year
Strong typhoons can occur year-round in the Northwest Pacific, but there has never been a landfalling typhoon as strong as Super Typhoon Nock-Ten so late in the year. After peaking as a Category 5 storm with 160 mph winds at 3 UTC Christmas Day (as per post-analysis by JTWC), Nock-Ten made landfall in the Philippines at 6 UTC Christmas Day, 2016 as a Category 4 storm with 155 mph winds and a central pressure of 915 mb. The only stronger typhoon ever recorded so late in the year was Super Typhoon Hester, which peaked as a Category 5 storm with 185 mph winds on December 31, 1952, about 1,000 miles east of the Philippines. Hester recurved out to sea without affecting any land areas. Nock-Ten’s formation was aided by ocean temperatures that were up to 1°C (1.8°F) warmer than average.


Figure 9. MODIS satellite image of Nock-Ten taken at approximately 06 UTC December 25, 2016. At the time, Nock-Ten was a Category 4 super typhoon with 155 mph winds, approaching the Philippines. Image credit: NASA.

Examples of a geographical shift in tropical cyclone activity in 2016
As I explained in my August 2014 post, Climate Change May Increase the Number of Hawaiian Hurricanes, warming sea surface temperatures may help shift the tracks of Eastern Pacific hurricanes closer to Hawaii. And for the third consecutive year, Hawaii saw a highly unusual level of tropical cyclone activity of activity in 2016, thanks, in part, to record- and near record-warm ocean temperatures.

July 23: Darby Hits Hawaii, Then Makes the Closest Pass to Honolulu by a Tropical Storm in Recorded History
Tropical Storm Darby made a direct hit on the Big Island of Hawaii on July 23, 2016, becoming just the fifth named storm since 1949 to make landfall on a Hawaiian Island. The next day, Darby made the closest approach on record by a tropical storm to the island of Oahu, which resulted in torrential rains in excess of 10 inches. Darby passed just 40 miles to the south and west of Honolulu with sustained winds of 40 mph. Darby’s formation was aided by ocean temperatures that were more than 1°C (1.8°F) warmer than average.


Figure 10. Another storm parade for Hawaii: VIIRS visible satellite image of ex-Hurricane Celia, Hurricane Darby, and Tropical Storm Estelle as seen on July 17, 2016. Image credit: NASA.

Examples of increased tropical cyclone rainfall in 2016
Increased evaporation from warmer oceans is expected to increase tropical cyclone rainfall by an average of 20% by the year 2100, agree hurricane scientists. Record- to near-record-warm ocean temperatures over the Atlantic waters near the U.S. in 2016 led to two instances of record- to near-record atmospheric moisture levels and record rainfall amounts in association with tropical systems: the “no-name” storm over Louisiana in mid-August, and Hurricane Matthew in October along the Southeast U.S. coast.

Mid-August: Louisiana’s No-name Storm
A slow-moving tropical disturbance that was never officially classified as a tropical depression meandered over Louisiana in mid-August, dumping colossal amounts of rain. The extreme record flooding that resulted caused 13 deaths and an estimated $10 - 15 billion in damage, making it the most expensive natural disaster in the U.S. in 2016. Some parts of Louisiana recorded more than 20" of rain in 48 hours, which qualifies as a 1-in-1,000 year rainfall event (having a 0.1 percent chance of occurring at a particular location in any given year), according to the NWS Lower Mississippi River Forecast Center. The highest rainfall total from the storm was 31.39” in Watson, Louisiana. The storm system carried near-record amounts of atmospheric moisture, drawn from the Gulf of Mexico and northwest Atlantic, where sea-surface temperatures (SSTs) were at near-record levels—more than 1°C (1.8°F) warmer than average. A fast-track climate change attribution study published one month after the storm found that climate change approximately doubled the chances for the type of heavy downpours that caused the devastating flood.

This was Louisiana’s second 20” deluge of the year; on March 8 - 12, an upper-level low pressure system stuck in place over Texas brought a flow of moist Gulf of Mexico air with record levels of atmospheric moisture for this time of year to Louisiana, resulting in widespread 1-in-200 year rainfall amounts of 15 - 20”. The storm killed five, and total damage in Louisiana and Texas was estimated at $1.5 billion by insurance broker Aon Benfield.


Figure 11. Major flooding in Prairieville, Louisiana on August 12, 2016 from a no-name tropical disturbance that caused $10 - $15 billion in damage. Image credit: @presleygroupmk/twitter.com.

October 7 - 9: Hurricane Matthew Brings Record Rains and a Record Storm Surge to the Southeast U.S.
The main story of the 2016 Atlantic hurricane season was Hurricane Matthew, the Atlantic’s first Category 5 storm since Felix of 2007. Matthew lasted as a major hurricane for eight days from Sept. 30 to Oct. 7, and devastated Haiti as a Category 4 storm on October 4, killing at least 546, making it the Atlantic’s deadliest hurricane in 11 years. Matthew grazed the coast of Florida and Georgia before making landfall in South Carolina on October 8 as a Category 1 hurricane with 75 mph winds. Matthew’s storm surge brought water levels that were the highest ever observed along portions of the coasts of Northern Florida, Georgia and North Carolina, beating records that had been set as long ago as 1928. Some of these records—and much of the coastal damage—would not have occurred without sea level rise over the past century from human-caused global warming. In addition, near record-warm ocean waters more than 1°C (1.8°F) warmer than average contributed to atmospheric moisture levels that were the highest on record over portions of Florida and South Carolina as Matthew moved up the coast, allowing the hurricane to dump 1-in-1000 year rains in some areas of South Carolina and North Carolina. Matthew killed 49 people in the U.S., 28 of them in North Carolina, and U.S. damage was estimated at up to $10 billion. This would make Matthew the 17th most expensive hurricane in U.S. history.


Figure 12. Twenty-four hour rainfall amounts from Hurricane Matthew on October 6 - 10, 2016 over portions of South Carolina and North Carolina were so extreme, that one could expect them to have a recurrence interval of 1-in-1000 years based on past climatology (dark blue colors).

Links
Hurricane Patricia's 215 mph Winds: A Warning Shot Across Our Bow (my 2016 blog post)
Fewer but Stronger Global Tropical Cyclones Due to Ocean Warming (my 2015 blog post)
Hurricanes and Climate Change: Huge Dangers, Huge Unknowns (my 2013 blog post)
Climatesignals.org analysis of Hurricane Matthew
Climatesignals.org analysis of Super Typhoon Meranti

Jeff Masters

Hurricane Climate Change

Nightmare on Christmas: Super Typhoon Nock-Ten Pounds the Philippines

By: Jeff Masters , 5:09 PM GMT on December 26, 2016

Super Typhoon Nock-Ten struck the Philippines on Christmas Day as a Category 4 storm with 155 mph winds, making it the strongest landfalling typhoon on record anywhere in the Northwest Pacific so late in the year. Only two non-landfalling typhoons have been as strong as Nock-Ten so late in the year: Super Typhoon Hester, which peaked as a Category 5 storm with 185 mph winds on December 31, 1952, about 1,000 miles east of the Philippines, and Super Typhoon Susan, which peaked at 155 mph winds in a similar location on December 27, 1963. Nock-Ten peaked in intensity on Saturday morning, when the Joint Typhoon Warning Center (JTWC) estimated that the storm had sustained 1-minute winds of 155 mph and the Japan Meteorological Agency estimated a 915 mb central pressure.


Figure 1. MODIS satellite image of Nock-ten taken at approximately 06 UTC December 25, 2016. At the time, Nock-ten was a Category 4 super typhoon with 155 mph winds, approaching the Philippines. Image credit: NASA.

It is too early to know what sort of damage or casualties Nock-Ten may have inflicted, but the destruction is likely to be significant. Here are the details on the four landfalls Nock-Ten made, courtesy of Aon Benfield:

1ST LANDFALL: 
LANDFALL LOCATION: Bato, Catanduanes, Philippines
. LANDFALL TIMEFRAME: 06:30PM PHT local time, December 25 (10:30 UTC)
. LANDFALL INTENSITY: 250 kph (155 mph) - Category 4



2ND LANDFALL:
 LANDFALL LOCATION: Sagnay, Camarines Sur, Philippines.
 LANDFALL TIMEFRAME: 09:30PM PHT local time, December 25 (13:30 UTC)
. LANDFALL INTENSITY: 240 kph (150 mph) - Category 4



3RD LANDFALL:
 LANDFALL LOCATION: San Andres, Quezon, Philippines. 
LANDFALL TIMEFRAME: 02:00AM PHT local time, December 26 (18:00 UTC, December 25). 
LANDFALL INTENSITY: 185 kph (115 mph) - Category 3



4TH LANDFALL:
 LANDFALL LOCATION: Marinduque, Philippines
. LANDFALL TIMEFRAME: 04:30AM PHT local time, December 26 (20:30 UTC, December 25). 
LANDFALL INTENSITY: 185 kph (115 mph) - Category 3

The strongest Christmas Day typhoon on record for the Philippines
Nock-Ten was not the first typhoon to hit the Philippines on Christmas Day, but it was the strongest. The other two typhoons to hit the islands on Christmas Day were Category 2 Typhoon Lee in 1981 and Category 2 Typhoon Jean in 1947. The worst tropical cyclone in world history to strike on Christmas Day was Category 3 Cyclone Tracy, which devastated Darwin, Australia in 1974, killing 71 people and destroying 80% of the homes in the city.

According to NOAA’s historical hurricane archive, only seven major typhoons of Category 3 or stronger intensity have hit the Philippines in December:

Category 4 Typhoon Harriet on December 31, 1959 (145 mph winds)
Category 3 Typhoon Opal on December 14, 1964 (115 mph winds)
Category 4 Typhoon Nanmadol on December 2, 2004 (135 mph winds)
Category 3 Typhoon Hagupit on December 6, 2014 (125 mph winds)
Category 5 Typhoon Gilda on December 18, 1959 (160 mph winds)
Category 4 Typhoon Manny on December 9, 1993 (130 mph winds)
Category 5 Typhoon Bopha on December 3, 2012 (170 mph winds)

Note: the charts and advisories are not working on our main site for Nock-Ten; please use our mobile site to get the tracking maps and advisories for the storm.

Jeff Masters

Hurricane

Super Typhoon Nock-Ten Heads for a Christmas Day Landfall in the Philippines

By: Jeff Masters , 6:24 PM GMT on December 24, 2016

Typhoon warnings are flying in the Philippines as Super Typhoon Nock-Ten steams westwards at 8 mph towards the Philippine island of Catanduanes. Nock-Ten is expected to make landfall there on Christmas Day as a major Category 3 or 4 storm, then continue westwards, gradually weakening due to land interaction, passing very close to the capital of Manila on Luzon Island the day after Christmas as a Category 1 storm. Nock-Ten likely peaked in intensity on Saturday morning, when the Joint Typhoon Warning Center (JTWC) estimated that the storm had sustained 1-minute winds of 150 mph and the Japan Meteorological Agency estimated a 915 mb central pressure. Satellite loops late Saturday morning showed that Nock-Ten had grown slightly less organized compared to early Saturday morning, with an eye that was less distinct. Some erosion of the storm’s eyewall on the west side was apparent, likely caused by dry air to the west. Microwave satellite imagery on Saturday morning showed that Nock-Ten had developed a tiny 6-mile diameter eye surrounded by a concentric outer eyewall, indicating that an eyewall replacement cycle (ERC) might be underway. During an ERC, the inner eyewall gets unstable and collapses, resulting in a temporary weakening of the storm by 10 - 20 mph for up to 24 hours, until the outer eyewall can stabilize and take over as the the storm’s main eyewall. With Nock-ten experiencing low wind shear of 5 - 10 knots and traversing very warm waters of 29°C (84°F)—1°C (1.8°F) above average—re-intensification after the ERC completes is possible, and satellite imagery early Saturday afternoon did show Nock-Ten had become more organized, with a prominent eye reappearing. However, the storm doesn’t have much time to intensify before interaction with land starts to weaken the typhoon, and dry air to the west may also interfere with intensification. Thus, it is unlikely that Nock-Ten will achieve Category 5 status.


Figure 1. MODIS satellite image of Nock-ten taken at approximately 06 UTC December 24, 2016. At the time, Nock-ten was a Category 4 super typhoon with 150 mph winds, approaching the Philippines. Image credit: NASA.

The strongest Christmas Day typhoon for the Philippines
Nock-Ten will not be the first typhoon to hit the Philippines on Christmas Day, but it will likely be the strongest. The other two typhoons to hit the islands on Christmas Day were Category 2 Typhoon Lee in 1981 and Category 2 Typhoon Jean in 1947. The worst tropical cyclone in world history to strike on Christmas Day was Category 3 Cyclone Tracy, which devastated Darwin, Australia in 1974, killing 71 people and destroying 80% of the homes in the city.

According to NOAA’s historical hurricane archive, only seven major typhoons of Category 3 or stronger intensity have hit the Philippines in December:

Category 4 Typhoon Harriet on December 31, 1959 (145 mph winds)
Category 3 Typhoon Opal on December 14, 1964 (115 mph winds)
Category 4 Typhoon Nanmadol on December 2, 2004 (135 mph winds)
Category 3 Typhoon Hagupit on December 6, 2014 (125 mph winds)
Category 5 Typhoon Gilda on December 18, 1959 (160 mph winds)
Category 4 Typhoon Manny on December 9, 1993 (130 mph winds)
Category 5 Typhoon Bopha on December 3, 2012 (170 mph winds)

If Nock-Ten hits the Philippines with 145 mph winds or stronger, it will be the strongest landfalling storm in the Philippines so late in the year. The strongest non-landfalling typhoon ever recorded so late in the year was Super Typhoon Hester, which peaked as a Category 5 storm with 185 mph winds on December 31, 1952, about 1,000 miles east of the Philippines. Hester recurved out to sea without affecting any land areas.


Figure 2. Radar image of Nock-ten taken at approximately 1 pm EST December 24, 2016. Image credit: The Philippines’ weather service (PAGASA).

Nock-Ten likely to be a highly destructive storm for the Philippines
The projected track and intensity of Nock-Ten over the Philippines are similar to that of Typhoon Rammasun of July 2014, which killed 106 people and did $871 million in damage to the country, making it the third costliest typhoon in Philippines’ history, behind Haiyan of 2013 ($2 billion) and Bopha of 2012 ($1 billion], After making its initial landfall to the east of Manila as a Category 4 storm, land interaction weakened Rammasun to Category 2 strength with 100 mph winds as it moved over Manila. Rammasun caused widespread havoc in the city of 12.8 million, leaving at least 90% of the residents of metropolitan Manila without power due to toppled poles and downed lines. Nock-ten is expected to be a weaker Category 1 storm when it passes over Manila, and its damage should be lower than that of Rammasun's. Still, damage from Nock-Ten could reach $500 million, which would make it the Philippines’ fifth most destructive typhoon in history. Rainfall from Nock-Ten is expected to exceed 8 inches over the core of its path, according to the 6Z Saturday run of the HWRF model.

Storm surge risk
The Philippines’ weather service (PAGASA) is warning of storm surge heights of up to 2.5 meters (8.2’) near where Nock-Ten makes its initial landfall, on the eastward-facing coastal areas of Camarines Sur, Camarines Norte and Catanduanes. Metro Manila, with approximately 12.8 million people, is also at risk of a damaging storm surge. However, surge heights will be lower there, due to the fact Manila faces to the west, away from the direction the storm is approaching from—and the fact that Nock-Ten should weaken to Category 1 strength before reaching Manila.

Recent research suggests that a worst-case storm like Super Typhoon Haiyan with 190 mph winds—if it were to follow the track of several historical typhoons—could bring a catastrophic storm surge of 3.9 to 5.6 m (13 - 18’) along the western seaboard of Metro Manila, even after the storm weakens due to passing over the land areas required to get to Manila. This was the conclusion of a poster presentation at last week’s meeting of the American Geophysical Union by John Kenneth Belena Suarez of the National Institute of Geological Sciences, University of the Philippines, titled Possibility Of Generating Significant Storm Surge On The Western Seaboard Of Metro Manila, Philippines. The researchers studied historical typhoons since 1951 that had passed over Manila, like Rita of 1978, Collen of 1992, Sybil of 1995, Bebinca of 2000 and Xangsane of 2000. They concluded that if these storms had made their initial landfall as Category 5 super typhoons with 190 mph winds, they would have been able to generate storm surges of 3.9 to 5.6 m (13 - 18’) in Manila. Nock-Ten appears unlikely to be a worst-case storm, fortunately.

Note: the charts and advisories are not working on our main site for Nock-Ten; please use our mobile site to get the tracking maps and advisories for the storm.

Have a safe and happy holiday, everyone!

Jeff Masters

Hurricane

A Christmas Day Typhoon Headed for the Philippines

By: Jeff Masters , 6:31 PM GMT on December 23, 2016

Celebrations of Christmas Day in the Philippines this year will have to occur amid emergency declarations as Typhoon Nock-ten puts a huge lump of coal into the stockings of residents of the main Philippine Island of Luzon. Satellite loops on Friday afternoon showed that Nock-ten was undergoing rapid intensification. A prominent eye was developing, surrounded by an intense ring of eyewall thunderstorms with cold cloud tops. With Nock-ten experiencing low wind shear of 5 - 10 knots and traversing very warm waters of 29°C (84°F), which were 1°C (1.8°F) above average, intensification into a Category 4 storm by Sunday appears likely. Unfortunately, the storm is on track to pass over a very heavily populated area of the Philippines, including the capital of Manila.


Figure 1. MODIS satellite image of Nock-ten taken at approximately 06 UTC December 24, 2016. At the time, Nock-ten was a Category 4 super typhoon with 150 mph winds, approaching the Philippines. Image credit: NASA.

A rare out-of-season typhoon for the Philippines
Strong typhoons are rare in December in the Philippines. According to NOAA’s historical hurricane archive, only seven major typhoons of Category 3 or stronger intensity have hit the Philippines in December:

Category 4 Typhoon Harriet on December 31, 1959 (145 mph winds)
Category 3 Typhoon Opal on December 14, 1964 (115 mph winds)
Category 4 Typhoon Nanmadol on December 2, 2004 (135 mph winds)
Category 3 Typhoon Hagupit on December 6, 2014 (125 mph winds)
Category 5 Typhoon Gilda on December 18, 1959 (160 mph winds)
Category 4 Typhoon Manny on December 9, 1993 (130 mph winds)
Category 5 Typhoon Bopha on December 3, 2012 (170 mph winds)

The Philippines—a heavily Catholic nation—is having a bad run of luck for typhoons hitting on major holy days. Just last year, the Philippines suffered their first typhoon ever recorded on Easter Sunday—Typhoon Maysak. Fortunately, Maysak was weakening rapidly at landfall, and caused no deaths or major damage. Nock-ten will be just the third typhoon on record to hit the Philippines on Christmas Day. The others were Category 2 Typhoon Lee in 1981 and Category 2 Typhoon Jean in 1947. The worst tropical cyclone in world history to strike on Christmas Day was Category 3 Cyclone Tracy, which devastated Darwin, Australia in 1974, killing 71 people and destroying 80% of the homes in the city.

Have a safe and happy holiday, everyone, and I’ll be back with an update on Nock-ten this weekend.

Jeff Masters

Hurricane

Betting on a White Christmas, U.K.-Style

By: Bob Henson , 5:30 PM GMT on December 21, 2016

Millions of Americans watch and wait for the potential of a white Christmas each year, but in the United Kingdom, people put their money where their forecast is. Unlike the United States, betting on weather events is legal in the U.K., and snowfall on Christmas Day is just one of the many atmospheric phenomena on which Brits can place bets. In April 2011, for example, one betting firm was offering 4-to-11 odds that Britain would be hotter than the Mediterranean holiday island of Ibiza on an upcoming holiday weekend, and 3-to-1 odds that it would rain in London during the royal wedding of Prince William and Catherine Middleton. Last Friday, nine days before Christmas, bookies set 8-to-1 odds that London would see snowfall on December 25, meaning that bettors would collect $8 for every $1 they bet on a white Christmas. That prospect looks very unlikely now, with temperatures expected to approach 60°F (16°C).


Figure 1. Rooftops of houses in the town of Luton, England, are covered with snow on December 22, 2009. Heavy snowfall resulted in cancelled flights and train trips across the country. Image credit: Oli Scarff/Getty Images.

A snow-frosted British Christmas: more fable than fact
Those who dare to bet on snow in London for Christmas will usually be disappointed. Our image of a snowy England during the holidays was largely the doing of Charles Dickens, author of “A Christmas Carol.” When Dickens was growing up in London during the 1810s, near the tail end of the Little Ice Age, there were reportedly six white Christmases in just a decade’s time, and this experience likely colored his later writings. Actually, snowfall across England is more likely to occur in January, February, and March than in December, thanks to the delay in winter cooling produced by the surrounding ocean. Another factor that made white Christmases even more common in England prior to 1752 was a timekeeping quirk. The British changeover from the Julian to the Gregorian calendar meant that Christmas suddenly moved up by 12 days relative to the winter solstice, which pushed the holiday away from the climatologically snowier period that occurs well after the solstice.

In our warmer 21st-century climate, snow cover at Christmas is fairly uncommon across the British Isles. The UK Met Office defines a white Christmas as when at least one snowflake is observed between midnight and midnight on December 25 (no accumulation required). By this definition, most years produce a “white Christmas” at least somewhere in the UK, but only 4 of the last 52 years have produced widespread snow cover (defined as more than 40% of UK stations reporting snow on the ground at 9 AM). Two standouts in recent years were Christmas 2009 and 2010, both of which saw widespread snows of a few inches and a solidly white Christmas in many areas. A total of 83% of British observation sites reported snow on the ground in 2010, which is the largest coverage for any year in reliable snowfall records that date back to the 1960s. In contrast, 2015 saw the UK’s warmest December on record, with no snow cover anywhere in the nation on Christmas Day (although it still counted as a white Christmas on the national scale because 10% of stations reported at least a flake falling).


Figure 2. Britain was almost completely snow-covered on January 7, 2010, following days of heavy snow. Image credit: Jeff Schmaltz, MODIS Rapid Response Team, NASA/GSFC, via Wikimedia Commons.


Figure 3. Historical odds of a white Christmas, in percentages, based on data from 1981 to 2010. Image credit: NOAA.


Figure 4. Predicted departure from average temperature (in degrees °C; multiply by 1.8 for degrees °F) for 18Z (1:00 pm EST) Sunday, December 25, 2016, as projected by the GFS model run at 12Z Wednesday. Below-average readings will predominate west of the Rockies, with afternoon temperatures up to 20°F - 25°F above average in the central states. Despite the mildness, most areas should end up falling short of record highs, especially in parts of the East Coast where Christmas Day 2015 was by far the warmest on record. Image credit: tropicaltidbits.com.

The U.S. white-Christmas outlook: not too far from climatology
As of Wednesday, the odds for a white Christmas 2016 in the United States are fairly close to what one might expect: highest in the mountainous West and along the northern tier of states, where recent storms have already dropped a decent snowpack, but virtually nil from the central Plains to the Eastern Seaboard and southward. As a strong upper-level storm approaches the central states, mild air will be pumped north across the lower- and mid-Mississippi Valley. Instead of snow, severe thunderstorms could erupt on Christmas Day across parts of the Southern Plains, especially Oklahoma, according to the long-range outlook issued Wednesday by NOAA's Storm Prediction Center. Further north, a swath of heavy, windblown snow will likely shift from Wyoming and Montana across the Dakotas and into northern Minnesota from Sunday into Monday. Many of the nation’s largest cities in the East, Midwest, and South saw their last white Christmas in either 2009 or 2010, which were harsh winters in the U.S. as well as Britain.

You can find up-to-the-minute forecasts of where snow is expected over the holiday weekend, plus lots of additional background, at a special weather.com page.

The Weather Company tops new analysis of forecast accuracy
A major analysis of more than 139 million forecasts issued by public and private firms in the United States, Asia-Pacific, and Europe finds that those from The Weather Company, an IBM Business (which includes Weather Underground), come out on top. The study, produced by the U.S.-based verification firm ForecastWatch, examined the percentage of high and low temperature forecasts that fell within 3°F of the observed noon-to-midnight highs and midnight-to-noon lows, as well as the percentage of time that icons predicting precipitation or no precipitation on a calendar day were correct. The Weather Channel (via weather.com) and/or Weather Underground showed the greatest accuracy for 34 out of 45 regional and lead-time groupings in the study, which spanned time periods from 2010 to mid-2016 for the U.S. and 2013 to mid-2016 for Asia-Pacific and Europe.

“Our users and clients turn to us to help them make weather-related decisions with confidence. This study shows The Weather Company as the undisputed accuracy leader, confirming the trust of more than 250 million people who choose The Weather Company for weather information every month,” said Mary Glackin, senior vice president of science and forecasting operations at The Weather Company. “Making a claim is easy, but backing it up takes continued effort and focus on who you’re serving. With IBM, we’ve stepped up investment and made a dedicated effort toward advancing our forecasting skill in 2016.”

See the IBM news release for more on the forecast technologies used by The Weather Channel and Weather Underground, as well as a link to the full analysis from ForecastWatch. We’ll be back on Friday with a new post.

Bob Henson


Figure 5. David Karnovsky, general counsel for the New York City Department of City Planning, cross-country skis down West 73rd Street towards Central Park on December 27, 2010. A blizzard that pounded the U.S. East Coast delivered 20 inches of snow to New York City while snarling post-Christmas travel. Image credit: Andrew Burton/Getty Images.


Winter Weather

Earth on Pace For Its Warmest Year on Record After a 5th Warmest November

By: Jeff Masters , 8:18 PM GMT on December 19, 2016

November 2016 was Earth's fifth warmest November since record keeping began in 1880, said NOAA's National Centers for Environmental Information (NCEI) on Monday. November 2016 was 0.73°C (1.31°F) warmer than the 20th-century November average, but 0.23°C (0.41°F) cooler than the record warmth of 2015. NASA reported that November 2016 was the second warmest November in its database, behind November 2015. The difference between the two data sets is, in large part, due to how they handle the data-sparse areas in the Arctic, which was record warm in November. NOAA does not include most of the Arctic in their global analysis, while NASA does.


Figure 1. Departure of temperature from average by region for November 2016, the fifth warmest November for the globe since record keeping began in 1880. Record warmth was observed across parts of central and southeastern Canada, some areas across the far northern tier of the United States along with a portion of the southwest U.S., parts of western and southern Mexico, sections of eastern and west central Africa, a few parts of northern South America, and regions of some southeastern Asia island nations. Cooler-than-average conditions were observed across much of the central Eurasian continent, with monthly temperatures at least 5°C (9°F) below average in central Russia and parts of northeastern Asia. In South America, central Bolivia experienced record cold temperatures during November. Image credit: NOAA National Centers for Environmental Information (NCEI).

A weak La Niña event is now underway in the Eastern Pacific, and the cool waters present there have helped cool the planet slightly below the record warm levels observed during the strong El Niño event that ended in May 2016. The fact that November 2016 was still the 2nd to 5th warmest November on record despite the presence of La Niña can mostly be attributed to the steady build-up of heat-trapping greenhouse gases due to human activities. NOAA’s global surface temperature for the year so far (January-November 2016) is an impressive 0.94°C (1.69°F) above the 20th-century average and 0.07°C (0.13°F) warmer than the previous January-to-November record, set in 2015. Remarkably, no continental land areas were cooler than average for the year-to-date. It is almost certain that 2016 will end up as the warmest year on record for the planet, giving Earth three consecutive warmest years on record.

Ocean-only, land-only, and lower atmosphere temperatures in November
Ocean-only temperatures this November were the second warmest on record, while land-only temperatures were the 12th warmest on record. (Since most of Earth’s surface is covered by ocean, the land-plus-ocean reading is dominated by the ocean-only temperatures, thus keeping November 2016 so warm globally.) For the lowest 8 km of the atmosphere, global satellite-measured temperatures in November 2016 and for the Jan - Nov year-to-date period were the warmest in the 38-year record, according to the University of Alabama in Huntsville (UAH). For the stratosphere, the year-to-date temperatures were the coldest on record. Stratospheric cooling is a classic symptom of an increase in greenhouse gases in the atmosphere—the upper atmosphere must cool to compensate for warming near the surface.


Figure 2. Departure from the 20th-century average for the global January-through-November temperature for the years 1880 - 2016. This year has seen by far the warmest temperatures on record for the year-to-date period. Image credit: NOAA/National Centers for Environmental Information (NCEI).

Arctic sea ice hits its lowest November extent on record
November 2016 Arctic sea ice extent was the lowest in the 38-year satellite record, according to the National Snow and Ice Data Center (NSIDC). The record low was due to unusually high air temperatures, winds from the south, and a warm ocean. For a brief period in the middle the month, total extent actually decreased by 50,000 square kilometers (9,300 square miles.) The only other November retreat of Arctic sea ice in the 38-year satellite record was a less pronounced and brief retreat of 14,000 square kilometers (5,400 square miles) that occurred in 2013. Seven of the eleven months of 2016 have seen record-low Arctic sea ice, and the annual sea ice minimum in September was the second lowest on record.

Sea ice around Antarctic was also extraordinarily low in November--more than 1 million sq km below the previous monthly record, from 1986. The monthly value was 5.7 standard deviations below the long-term average, a mammoth departure and more than twice as large as the previous record. Sea-ice formation processes are largely decoupled between the Arctic and Antarctic, so there is no obvious direct link between the record-low values at the two poles in November.


Figure 3. Daily mean temperatures by Julian day through December 18, 2016 over the Arctic north of 80°N, as compiled by the Danish Meteorological Institute (DMI). Temperatures for this year (red line) are compared to the long-term averages (green line.) Temperatures in October, November, and the first half of December were 5 - 20°C (8 - 36°F) above average. This is by far the warmest multi-month anomaly measured since DMI began tracking Arctic temperatures in 1956. According to the 2016 Arctic Report Card, issued last week, the average surface air temperature of the Arctic for the year ending September 2016 was by far the highest since 1900, and new monthly record highs were recorded in January, February, October and November 2016.

No billion-dollar weather disasters in November 2016
According to the November 2016 Catastrophe Report from insurance broker Aon Benfield, no billion-dollar weather-related disasters hit the planet in November. However, one event from October—Super Typhoon Chaba in South Korea and Japan—accumulated enough damage claims to be rated a billion-dollar disaster by the end of November. From January through November 2016, there were 30 billion-dollar weather disasters globally. This is the fourth greatest number of such disasters in any year since 1990. Only 2013 (41), 2010 (40), and 2011 (35) had more. For the U.S., Aon Benfield counted thirteen billion-dollar weather disasters during January - November 2016, which is the second highest number of such disasters on record since 1980 (the record: sixteen in 2011.)

Here is Aon Benfield’s tally of billion-dollar weather disasters globally for January - November 2016:

1) Flooding, Yangtze Basin, China, 5/1 - 8/1, $28.0 billion, 475 killed
2) Hurricane Matthew, Caribbean, Bahamas, U.S., 9/28 - 10/10, $15.5 billion, 603+ killed
3) Flooding, Louisiana U.S., 8/9 - 8/16, $10 - $15 Billion, 13 killed
4) Drought, China, 6/1 - 8/31, $6 billion, 0 killed
5) Flooding, Germany, France, Austria, Poland, 5/26 - 6/6, $5.5 billion, 17 killed
6) Drought, India, 1/1 - 6/30, $5.0 billion, 0 killed
7) Flooding, Northeast China 7/16 - 7/24, $4.7 billion, 289 killed
8) Wildfire, Fort McMurray, Canada, 5/2- 6/1, $4.5 billion, 0 killed
9) Severe Weather, Plains-Southeast U.S., 4/10 - 4/13, $4.3 billion, 1 killed
10) Drought, Thailand, 1/1 - 6/30, $3.3 billion, 0 killed
11) Severe Weather, Rockies-Plains-Southeast-Midwest U.S., 3/22 - 3/25, $2.5 billion, 0 killed
12) Super Typhoon Meranti, China, Taiwan, Philippines, 9/13 - 9/16, $2.5 billion, 44 killed
13) Flooding, China, 6/18 - 6/23, $2.3 billion, 68 killed
14) Flooding, Texas U.S., 4/15 - 4/19, $2.0 billion, 9 killed
15) Winter Weather, East Asia, 1/20 - 1/26, $2.0 billion, 116 killed
16) Severe Weather, Plains-Midwest U.S., 4/29 - 5/3, $1.8 billion, 6 killed
17) Tropical Cyclone Roanu, Sri Lanka, India, Bangladesh, Myanmar, China, 5/14 - 5/21, $1.8 billion, 135 killed
18) Severe Weather, Plains-Rockies U.S., 7/28 - 7/29, $1.6 billion, 0 killed
19) Drought, Zimbabwe, 6/1 - 8/10, $1.6 billion, 0 killed
20) Flooding and Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 3/4 - 3/12, $1.5 billion, 6 killed
21) Super Typhoon Nepartak, Philippines, Taiwan, China, 7/8 - 7/12, $1.4 billion, 111 killed
22) Severe Weather, Plains-Southeast U.S., 3/17 - 3/18, $1.4 billion, 0 killed
23) Tropical Cyclone Winston, Fiji, 2/16 - 2/22, $1.4 billion, 44 killed
24) Flooding, Argentina and Uruguay, 4/4 - 4/10, $1.3 billion, 0 killed
25) Severe Weather, Plains-Midwest U.S., 5/21 - 5/28, $1.3 billion, 1 killed
26) Severe Weather, Plains-Midwest-Southeast-Northeast U.S., 2/22 - 2/25, $1.2 billion, 10 killed
27) Severe Weather, Netherlands, 6/23 - 6/24, $1.1 billion, 0 killed
28) Severe Weather, Plains-Midwest-Mississippi Valley U.S., 5/7 - 5/10, $1.0 billion, 2 killed
29) Winter Weather, Eastern U.S., 1/21 - 1/24, $1.0 billion, 58 killed
30) Super Typhoon Chaba, South Korea, Japan, 10/5 - 10/6, $1.0 billion, 10 killed

And here is the one new billion-dollar disaster from the November 2016 Aon Benfield report in more detail:


Disaster 1. Category 5 Super Typhoon Chaba peaked at 165 mph winds south of Okinawa, Japan on October 3 before weakening to a Category 1 storm as it grazed South Korea on October 5. Southern South Korea was the hardest-hit with ten killed and the large majority of the $1 billion in damage from the storm. In this image, we see an International Space Station view of the typhoon taken at 08 UTC October 3, 2016 when the storm was at peak intensity: a 905 mb central pressure and sustained winds of 165 mph.

Notable global heat and cold marks set in November 2016
Hottest temperature in the Northern Hemisphere: 41.6°C (106.9°F) at Matam, Senegal, 8 and 24 November
Coldest temperature in the Northern Hemisphere: -57.0°C (-70.6°F) at Summit, Greenland, 24 November
Hottest temperature in the Southern Hemisphere: 46.3°C (115.3°F) at West Roebuck, Australia, 5 November
Coldest temperature in the Southern Hemisphere: -60.6°C (-77.1°F) at Concordia, Antarctica, 1 November
(Courtesy of Maximiliano Herrera.)

Major weather stations that set (not tied) new all-time heat or cold records in November 2016 (Courtesy of Maximiliano Herrera)
Combarbala (Chile) max. 37.3°C, 3 November
San Lorenzo (Chile) max. 39.7°C, 3 November
Lay Lay (Chile) max. 40.5°C, 17 November
Esperantina (Brazil) max. 41.8°C, 25 November
Ambon (Indonesia) max. 36.2°C, 29 November
San Fernando (Chile) max. 36.4°C, 29 November
Twee Rivieren (South Africa) max. 45.6°C, 30 November

One all-time national heat record set or tied in November 2016
One nation or territory—The Comoros—set an all-time heat record in November 2016. From January through November 30, 2016, a total of 22 nations or territories tied or set all-time records for their hottest temperature in recorded history. This breaks the record of eighteen all-time heat records in 2010 for the greatest number of such records set in one year. Also, one all-time cold temperature record has been set so far in 2016 (in Hong Kong.) "All-time" record here refers to the warmest or coldest temperature ever reliably reported in a nation or territory. The period of record varies from country to country and station to station, but it is typically a few decades to a century or more. Most nations do not maintain official databases of extreme temperature records, so the national temperature records reported here are in many cases not official. Our data source is international weather records researcher 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. Here are 2016's all-time heat and cold records as of December 1:

The Comoros: November 13, 2016, 35.6°C (96.1°F) at Hahaya Airport (tie.)
French Guiana : September 27, 2016, 38.0°C (100.3°F) at Saint Laurent du Moroni.
The Marshall Islands: August 24, 2016, 35.6°C (96.1°F) at Utirik Atoll.
The Cayman Islands (United Kingdom territory) : August 21, 2016, 34.9°C (94.8°F) at Owen International Airport (tie.)
The British Virgin Islands [United Kingdom territory]: July 22, 2016, 35.0°C (95.0°F] at Terrance B. Lettsome International Airport.
Iraq: July 22, 2016, 53.9°C (129.0°F) at Basrah.
Iran: July 22, 2016, 53.0°C (127.4°F) at Delhoran (tie.)
Kuwait : July 21, 2016, when the mercury hit 54.0°C (129.2°F) at Mitribah.
Guernsey (United Kingdom territory): July 19, 2016, 35.0°C (95°F) at the small island of Alderney (tie.)
Hong Kong Territory (China): July 9, 2016, 37.9°C (100.2°F) at Happy Valley (tie.)
Niger: June 8, 2016, 49.0°C (120.2°F) at Bilma.
Palau: June 8, 2016, 34.4°C (93.9°F) at Koror AWS (tie.)
India : May 19, 2016, 51.0°C (123.8°F) at Phalodi.
Maldives: April 30, 2016, 35.0°C (95.0°F) at Hanimaadhoo.
Thailand: April 28, 2016, 44.6°C (112.3°F) at Mae Hong Son.
Cambodia: April 15, 2016, 42.6°C (108.7°F) at Preah Vihea.
Burkina Faso: April 13, 2016, 47.5°C (117.5°F) at Dori.
Laos : April 12, 2016, 42.3°C (108.1°F) at Seno.
Vanuatu in the South Pacific: February 8, 2016, 36.2°C (97.2°F) at Lamap Malekula.
Tonga: February 1, 2016, 35.5°C (95.9°F) at Niuafoou.
Wallis and Futuna Territory (France): January 10, 35.8°C (96.4°F) at Futuna Airport.
Botswana: January 7, 2016, 43.8°C (110.8°F) at Maun.

Hong Kong Territory (China) set its all-time coldest mark on January 24, 2016, -6.0°C (21.2°F) at Tai Mo Shan (elevation 950 meters.) Tai Mo Shan has a period of record going back to 1996; the coldest temperature near sea level since record keeping began at the Hong Kong Observatory in 1884 was 0°C (32°F) on January 18, 1893.

Jeff Masters

Climate Summaries

Cold Wave Crescendos with a Frigid Weekend

By: Bob Henson , 2:36 PM GMT on December 19, 2016

One of the sharpest cold fronts in recent years tore across the central and eastern U.S. this past weekend, leaving millions of Americans shivering in its wake. Packing wind chills below -50°F at times, the cold punch was a fitting climax to more than a week of off-and-on chill over large parts of the northern U.S. Extreme temperature contrasts were the norm with this front: for example, noontime readings across Georgia on Sunday ranged from 37°F with rain at Dalton, in the far north, to 83°F at Albany, in the far south. More than 1000 flights were cancelled on Friday and Saturday as bursts of snow struck in and near Denver and Chicago and a brief, high-impact round of freezing rain hit parts of the mid-Atlantic early Saturday morning. A horrifying 67-vehicle crash on ice-glazed I-95 in Baltimore, MD, killed two and injured more than 20 others, at least two in critical condition.


Figure 1. Darryl Hendricks moves into position on a breakwater to photograph sea smoke rising off the waters of Casco Bay, Maine, on Friday, Dec. 16, 2016, in South Portland. Hendricks risked both frostbite and being late for work in pursuit of what he called "the one shot I really wanted." The temperature dropped to -2°F with a wind chill of -25°F. Image credit: AP Photo/Robert F. Bukaty.


Figure 2. Pedestrians walk across a snowy street in downtown Kansas City, Missouri, on Saturday, Dec. 17, 2016. Image credit: AP Photo/Charlie Riedel.

A Texas-sized temperature swing
Grand prize for the most dramatic frontal passage goes to West Texas, where the cold air mass plowed south on Saturday in the form of a classic “blue norther” (sometimes called a Texas norther). A mesonet station about 6 miles west of Denver City, TX, reported a temperature drop of 36°F in just 10 minutes--from 21°C (70°F) to 1°C (34°F)--accompanied by winds of 40 knots (46 mph) gusting to 69 knots (79 mph). Thanks to Anton Seimon (Appalachian State University) for finding this nugget.

Temperatures across Texas at 4:00 pm CST Saturday ranged from 6°F at Dumas (nearby Dalhart sank to a record-low –8°F by Sunday morning) to a record-hot 92°F at McAllen. Midland set a record high of 80°F on Saturday afternoon, but by 11:59 pm CST, the city’s official temperature had plummeted to 18°F, just one degree short of the day’s record low! It was Midland's biggest one-day temperature spread for any date in records going back to 1930. More than a century ago, a blue norther on November 11, 1911 (11/11/11) managed to pull off the twin-record-in-one-day trick in both Oklahoma City, OK (83°F and 17°F) and Springfield, MO (80°F and 13°F). Both of these Oklahoma City records still stand.



Figure 3. In Big Lake, Texas, about 50 miles southeast of Midland, temperatures sank from around 80°F at 4:00 pm CST Saturday to near freezing by 6:00 pm and below 20°F by midnight. Times are shown for a 24-hour clock (15 = 1500 CST = 3:00 pm CST). Because the lower atmosphere was so well mixed on this day, the temperature traces are virtually identical at the indicated heights above ground of 1.5, 2, and 9 meters (roughly 4.9, 6.6, and 29.5 feet). Image credit: West Texas Mesonet, Texas Tech University.


Figure 4. It’s not hard to find the frontal boundary across the south-central U.S. in this model analysis from 18Z (noon CST) Saturday, December 17, 2016. Image credit: www.tropicaltidbits.com.

Serious cold in the nation’s heartland
Readings well below -20°F were scattered across the central and northern Great Plains into the Upper Midwest, and a few spots notched their coldest single night in many decades. Watertown, SD, dipped to -37°F on Sunday morning, just 3°F shy of its all-time low of -40°F (January 13, 1916). The reading smashed Watertown’s daily record of -24°F from 1983 and set a new monthly record for December. Data in Watertown goes back to 1893. In Limon, CO, a December record was also set, and an all-time record for any month tied, as the temperature bottomed out at -27°F before midnight Saturday. Limon’s climate data begins fairly recently, though, in 1970.

If it’s any comfort, many folks in Florida are ready for a touch of relief after a summerlike weekend of high humidity and temperatures soaring as high as 90°F. Miami’s low on Sunday was a balmy 79°F, tying the monthly record-warm minimum set on Dec. 2, 1901, and the day's average temperature of 82.5°F was a record for any December day since weather records began in Miami in 1892. Several other locations set daily record highs over the weekend across the South, even as daily record lows were being toppled just a few hundred miles to the north. We’ll see how the totals of record highs and lows stack up once the extreme pattern of this past weekend segues into a less-amplified setup this week.

Jeff Masters will be back later today with a roundup of November’s global climate.

Bob Henson


Winter Weather

A Close-Up Look at Southwestern Haiti, Post-Hurricane Matthew

By: Andrew Kennedy and Tracy Kijewski-Correa , 3:53 PM GMT on December 16, 2016

Today’s guest post is by Dr. Andrew Kennedy and Dr. Tracy Kijewski-Correa, associate professors in the Department of Civil & Environmental Engineering & Earth Sciences at the University of Notre Dame. From November 17 to 25, a reconnaissance team led by Kijewski-Correa visited the most-affected regions and evaluated Matthew’s effects on buildings, infrastructure, and the people of Haiti. Below, Dr. Kennedy and Dr. Kijewski-Correa give us a preliminary account of their trip, which took them to areas seen by relatively few outside observers since the hurricane. We'll be back on Monday with a new post. --Jeff Masters and Bob Henson

On October 4, 2016, Hurricane Matthew made landfall near the town of Les Anglais, Haiti, as a strong Category 4 storm with estimated sustained winds of 145 mph (65 m/s) (Fig. 1). The landfall region in the western Tiburon Peninsula, more than 150 miles west of the capital of Port-au-Prince, sustained extreme damage to buildings and vegetation. The Haitian government reported 546 fatalities from Matthew, while other sources reported at least 1600 unconfirmed deaths. Rainfall in the peninsula was extreme, estimated by NASA to be 10-20 inches over the course of the storm.

Figure 1. (a) Path of Hurricane Matthew over Haiti, showing inset on the western Tiburon Peninsula. (b) Inset of the Tiburon Peninsula, showing locations of figures. The hurricane icon shows the Saffir-Simpson category rating of Matthew at each location. Les Anglais (not shown) is on the southwest coast near the "213" highway icon, about 16 km (10 miles] east of the indicated landfall location. Background maps are from Google Earth.

Some background
Haiti is the poorest country in the Western Hemisphere, with a per-capita GDP of US$846 in 2014. Haiti has many poor people, a few very wealthy families, and a small, weak middle class. Even in the best of times, life is difficult here for most citizens, and these are not the best of times. Except for a few paved national roads that link large cities, many roads are unpaved and often impassable, intercepted by land/rock slides and rivers, and eroded by flash flooding. Four-wheel drive vehicles are necessary in many areas.

Haiti has a largely agricultural economy, historically focused on producing coffee and sugarcane but more recently on exporting oils used in perfumes, bananas, and cocoa. A large portion of the population, particularly in rural areas, survives on subsistence farming, so any interruption to agriculture has immediate impacts on nutrition. Overall, Haiti has little internal resilience to natural disasters and relies on outside aid not just for recovery, but for many of the basic services its citizens require.

Haiti is still recovering from a magnitude 7.0 earthquake in 2010 that killed at least 100,000 people, and perhaps several hundred thousand, in the general region of Port-au-Prince. Fortunately, areas affected by the 2010 Earthquake and Hurricane Matthew had relatively little overlap. All three major hurricane hazards played a significant role in Haiti during Hurricane Matthew: wind, waves/surge, and rainfall/flooding. All areas of the affected regions received strong wind, and most also experienced either saltwater flooding from the ocean, or freshwater flooding from rainfall.

Figure 2. Residential wind damage in housing types serving low, middle and upper class: (a) interior view of low-income home in Bonbon employing traditional Haitian metal hip roof framed with native timber that survived the hurricane thanks to the quick thinking of homeowners who tied framing at multiple locations with ropes and straps to reinforce load path during the storm; (b) side-by-side performance comparison of unreinforced masonry built in Bonbon by a foreign non-governmental organization with higher-quality imported materials (pink home), which survived despite loss of roof whereas neighboring middle-class homes built with locally-manufactured block was completely destroyed; (c) interior view of engineered upper-class home in Port Salut with well-connected metal-framed roof that bowed upward and pulled a two-story unreinforced masonry wall inward. Photo credits: Tracy Kijewski-Correa.

Wind-related storm effects
Strong winds during Matthew caused severe damage to most buildings employing lightweight roofs. Zinc metal roofs, which are used for most of the housing stock in the affected areas, were almost uniformly destroyed, leaving houses open to the elements (Fig. 2). Unconfined masonry walls, which are very common, were often tensioned by the uplift on the roof, making them easy to topple in the Category 4 winds. It was rare to find a metal-roofed building in the most affected areas that had not suffered significant damage. The best-performing buildings were built of heavy concrete block with concrete slab roofs; however, these types of buildings were deathtraps during the 2010 Earthquake.

All of this might seem to suggest that nothing can be done, but a few examples of good design stand out. Chief among them is a medical clinic in Port Salut, which was built according to modern design standards and suffered only minor loss of metal roof panels while buildings around it were severely degraded by the storm (Fig. 3). The night-and-day difference in performance indicates that it is possible to build safely in these regions, although adoption of safer practices for traditional building methods used in Haiti remains an ongoing challenge, overwhelmingly due to the lack of economic resources.

Figure 3. A tale of two medical facilities. Top: minor roof damage to a pediatric clinic in Port Salut, built in 2012, including (a) loss of metal roof panels on main clinic and (b) minor loss of hip flashing on outdoor triage area. Contrast this with the complete loss of the second floor of the main building of Hopital Saint Antoine in Jeremie, built in 1923 (bottom): (c) view from ground level, looking upward and roughly southward at the former location of original unreinforced masonry second floor; (d) view to the north, standing on the remains of floor joists of lost second floor where all unreinforced masonry walls, the wood-framed metal roof, and even floorboards were completely stripped away by strong easterly winds. Image credits: Alexandros Taflanidis, Notre Dame (Fig. 3a,b,d) and Tracy Kijewski-Correa (Fig. 3c).


In addition to building damage, winds uprooted or severely damaged many trees, including valuable coconut palms as well as avocado, breadfruit and mango trees. These will not recover for many years, inflicting not just a severe economic impact to market and export farmers but also eliminating a valuable food source relied on daily for survival by most families in this region. A more immediate concern is the destruction of ground crops such as the root vegetables Haitians call “vive” (life), the loss of bananas and plantains, and the loss of livestock. The staple crops will regrow in months through agricultural aid, but until this time, there is a severe food shortage in some areas that is still not being met. In addition to agricultural crops, the winds blew over many economically-valuable trees, including many fine examples of West Indian mahogany: there do not presently appear to be plans to take these windfalls to market. Opportunistic Haitians are instead planking the trunks into lumber and burning mounds of branches into charcoal – Haiti’s primary fuel source for cooking.

Wave- and surge-related storm effects
In the United States, beachfront regions are generally inhabited by a relatively well-off demographic who have resources to provide some resiliency in the event of a storm. In Haiti, beaches and other coastal areas are often homes for some of the poorest people: they may be fishermen who require daily access to the sea or those forced to low-lying regions as squatters without rights to land. Often, people are reluctant to evacuate in advance of a storm because of concerns about theft. This makes them highly vulnerable to storm surge and waves. Many people who evacuated did so only during the storm after water began to destroy their homes. While many received SMS (text) messages to evacuate, we were told unanimously that these messages never communicated the severity of the storm. Victims explained to us that they had experienced hurricanes before, but always had a home to return to. It was Matthew’s storm surge that took many by surprise.

Figure 4. High-elevation wave runup in a cliffed region near Roche a Bateau. The road here is approximately 17 feet (5.2 meters) above sea level. Photo Credit: A. Kennedy

Waves and storm surge in the Matthew-affected areas reached up to 15 - 25 feet (4.6 - 7.6 meters) above sea level in regions with steep beaches or cliffs (Fig. 4), and 5 - 15 feet (1.5 - 4.6 meters] in areas with more gentle beaches. Based on interviews with local residents, it appears that inundation often took the form of very fast, strong waves similar to those recorded in the Philippines during Super Typhoon Haiyan in 2013. Close to the ocean in the region of strongest inundation, almost all coastal buildings, again largely employing unreinforced masonry, were partially or completely destroyed (Fig. 5). These were often rebuilt into temporary structures from storm debris, salvaged materials, and blue tarp kits distributed by humanitarian agencies. Although exact numbers are still not clear, many thousands of homes and other buildings were completely destroyed by waves and surge, particularly on the southwest coast between Port Salut and Les Anglais. Damage was not as complete, though still significant, on the northern coast.

Figure 5. The remains of a school destroyed by wave runup near Coteau. Photo Credit: A. Kennedy.

Effects of rainfall and inland flooding
The Matthew-affected regions of Haiti received heavy rainfall during and after the storm. This did not cause as much structural damage as other hazards, but it degraded roads, damaged the contents of roof-compromised buildings, flooded entire districts in city centers, and hindered recovery efforts. The two largest of the affected cities, Jeremie and Les Cayes, both experienced inland flooding of around three feet in some downtown areas as the steep mountains outside the cities rapidly deposited their water in flatter coastal areas. Levees were overtopped in some coastal rivers, flooding adjacent areas. In the northern city of Jeremie, rainfall continued for weeks after Matthew: according to residents, this post-storm flooding was worse than that experienced during the storm.

The human cost
One may question if a nation this frail and aid-dependent could ever absorb and recover from two consecutive major disasters, even with sustained international involvement. This recovery will ride largely on the shoulders of individual homeowners, as the impacts of Hurricane Matthew, much like the 2010 Earthquake, have been felt most heavily in the residential sector. It has been six years since the earthquake and the housing sector has yet to recover, with many families in Port-au-Prince and Leogane still inhabiting transitory and informal shelters, struggling over issues of land tenure, and lacking access to mortgages to rebuild. Indeed, homes are often overlooked in disaster risk reduction programming and humanitarian recovery efforts. That was the case in the 2010 Earthquake, and it will be the case again in the wake of Matthew. Those that completely lost their homes will join their countrymen in what may be a decade-long recovery of their homestead. Yet unlike those recovering from a “dry” seismic event, there was little to salvage after Matthew. Its victims often had all that they possessed washed out to sea or completely destroyed by the onslaught of heavy rains.

The story of Matthew’s actual disaster will take decades to unfold. In the short term, Matthew maimed the population with flying debris from metal roofs; incubated mold, disease and infection; destroyed sanitation systems; and inundated water supplies, resulting in a spike in cholera outbreaks. In one swoop, Matthew stripped a region of its agricultural assets, bringing not just the complete disruption of livelihoods but also the potential for famine both in the affected area and in major cities reliant on the peninsula's produce. Even the availability of fish and other marine life has been disrupted due to changes in the coastline.

Moreover, because Matthew swept over a large geographic area far removed from the capital and with frail road access, efforts to assess damage and deliver aid have been challenging. Coupling this geographic disconnect with “Haiti fatigue” among charitable donors, lingering distrust from reports of misappropriated earthquake recovery funds, and the Haitian government's role in limiting channels for disaster relief, one simple fact emerges: Matthew’s victims are struggling and will continue to struggle meeting the basic needs of life for some time to come. The tensions that are boiling in major cities like Les Cayes and Jeremie are a palpable sign of the frustration of Matthew’s victims, even though the losses in these cities pale in comparison to the smaller communities even further west.

Undoubtedly, the Haitian people have shown unparalleled resilience and perseverance in the face of extreme historical, political and natural disasters. Some argue they have had more bad luck than any people should bear. The impacts from the 2010 Earthquake and Hurricane Matthew are so severe that they make one wonder when, or even if, this amazingly resilient nation will be able to fully recover.

How you can help
If you wish to aid the recovery in the south of Haiti, please consider donations to one of these worthy charities working directly with populations in the affected regions:
GoServ Global--please indicate that you would like your donation directed toward recovery in Les Anglais, Haiti
Free the Kids--see Holiday Giving Catalog for donation options directed at agricultural recovery, food and housing

Andrew Kennedy and Tracy Kijewski-Correa, University of Notre Dame


Figure 6. Reconnaissance team (left to right). Back row: Lamarre Presuma (Engineering2Empower, Haiti), Scott Schiff (Applied Technology Council, USA), Onel Dossou (Engineering2Empower, Haiti), David Prevatt (University of Florida, USA), Michael Wilson (Logistics Lead, USA). Front row: Kwasi Perry (UAV Survey Inc., USA), Jac Lubin (Driver, Haiti), Alexandros Taflanidis (University of Notre Dame, USA), Edson Jean (Engineering2Empower, Haiti), Tracy Kijewski-Correa (University of Notre Dame, USA), Gede Jean Benoit (Engineering2Empower, Haiti), Brunie St-Fort (Driver, Haiti) and Andrew Kennedy (University of Notre Dame, USA).


Hurricane

Non-Historic, High-Awareness Winter Weather Grips U.S.

By: Bob Henson , 8:32 PM GMT on December 14, 2016

It’s beginning to feel a lot more like early winter across most of the United States after the warmest autumn on record. Several lobes of low pressure in the middle atmosphere, beneath the stratospheric polar vortex, have been swinging across the Midwest and Northeast U.S. These lobes are pushing large masses of Arctic surface air southward across the bulk of the nation in a series of pulses, with only limited relief in between. Even the worst of the cold doesn’t look like it will be truly historic at ground level. Still, some places will see their most frigid December conditions in several years. Cold and snow don’t have to be record-shattering in December to pack a noticeable punch.


Figure 1. A lone runner makes his way through Eagle Creek Park in Indianapolis, IN, as snow falls on Tuesday, Dec. 13, 2016. Image credit: AP Photo/Darron Cummings.


Figure 2. Extremely cold air in the middle atmosphere was pooled in central Canada, as shown by the light colors on this depiction of the height of the 500-mb surface (about midway up through the atmosphere). Values on the right-hand side are shown in tens of meters. Contours of surface air pressure (in black) show high pressure dominating the central U.S. Image credit: tropicaltidbits.com.

A week of wintry pulses
The latest phase of the cold wave was sweeping from the Midwest into the southern and eastern U.S. on Wednesday. Temperatures at midday were hovering a few degrees on either side of 0°F across most of Minnesota and the Dakotas. Strong northwest winds will push bitter cold across the East Coast corridor from Washington to Boston by Thursday, with temperatures tamped below freezing for at least a couple of days. Very light snow is possible for a few hours Wednesday night into Thursday, with another dose of wintry precipitation late Friday into Saturday. That round could have significant impacts for a few hours, as it falls onto already-cold road surfaces, until warmer air brings a transition from snow, sleet, and/or freezing rain to rain later Saturday. Capital Weather Gang warned of the potential for “an icy mess” on Saturday morning in the D.C. area.

Meanwhile, the next Arctic blast will push more frigid air into the central U.S., with a shield of light to moderate snow from the northern and central Rockies and Plains into the Upper Midwest. Denver may not get much above 0°F on Saturday, and single-digit lows could extend as far south as St. Louis, MO, on Sunday. Along the front, a band of thunderstorms is expected to drop a welcome 1” - 3” of rain across drought-hammered parts of the South, including northern Alabama and eastern Tennessee.


Figure 3. Winter weather alerts for the Great Lakes region as of Wednesday morning, December 14, 2016. Image credit: weather.com.

Lake effect machine kicks into overdrive
The most noteworthy snow this week will be in areas familiar to it: the lake-effect snow belts of the Great Lakes. Strong westerly winds associated with this week’s Arctic blasts will be passing over waters that have been unusually warm for this time of year (2°F to 4°F above average), leading to very unstable conditions that will favor snow-band formation. Areas in and near Buffalo, NY, and Cleveland, OH, could see periods of heavy snow with near-zero visibility on Wednesday into Thursday, although weather.com notes that the heaviest amounts may stay just south and east of Cleveland and Buffalo. (See embedded radar loop at bottom.)

Still more record highs than lows for December thus far
Largely because winter warmth is a welcome arrival to many, record highs in winter don’t grab the same attention as record lows. This week has already seen quite balmy conditions across the Gulf Coast and Southeast, and the region will see a brief recovery in temperatures over the weekend in between cold blasts. Monday’s high of 81°F was the warmest December day on record in Galveston, TX, in data going back to 1873. On the national scale, this warmth has actually been more exceptional than the cold observed further north. According to preliminary data from NOAA, the first few days of December (Dec. 1 - 12) saw 104 daily record highs in the U.S., but only 67 daily record lows. That ratio will tighten or even flip over the next few days, but don’t expect anything as out-of-whack as the 48-to-1 ratio of U.S. daily record highs to lows that occurred in November.


Figure 4. Strong northerly flow in mid-levels of the atmosphere (shown by white arrows) pushed very cold air southward at 18Z (1:00 pm EST) on December 23, 1983, near the peak of the great December 1983 cold wave. Red colors in the north-central U.S. denote the coldest air at 850 mb, about a mile above sea level. Yellow contours show the height (in decameters) of the 500-mb surface, near the vertical midpoint of the atmosphere. Image credit: National Weather Service/Dodge City, KS.

Echoes of a colossal December cold wave
We haven’t seen anything in recent decades like the truly historic cold wave that struck in December 1983. As noted by Eric Fisher (WBZ/Boston) and Angela Fritz (Capital Weather Gang), that memorable blast happened to follow the “super” 1982-83 El Niño event, which was roughly as strong as last winter’s 2015-16 El Niño event. The other comparably strong El Niño was in 1997-98; the following December (1998) ended up among the warmer Decembers in U.S. weather history but still produced some intense regional cold toward month’s end. In all three cases, the Pacific had swung from a very strong El Niño state into weak to moderate La Niña conditions by December.

Archives kept by meteorologist Guy Walton show that December 1983 produced a phenomenal 14,482 daily record lows and only 676 record highs. On December 24, barometric pressure (converted to sea-level equivalent) reached 1064 mb (31.42”) in Miles City, MT, the highest surface pressure on record for the contiguous U.S. according to WU weather historian Christopher Burt. Temperatures in mid- to late December 1983 plummeted to extreme values almost everywhere east of the Rockies, especially across the central third of the country. At Sioux Falls, SD, readings dipped below 0°F on December 16 and didn’t rise above zero again until December 25. Christmas Eve (December 24) brought a low of -25°F in Chicago, with wind gusts up to 41 mph. Christmas morning (December 25) saw low temperatures dip to 0°F as far southeast as Little Rock, AR, with a high of just 12°F. Even Tampa, FL, only reached a Christmas Day high of 38°F, as noted by weather.com’s Jon Erdman in a roundup of great American cold waves.

The average temperature for December 1983 in Minneapolis was 3.7°F, the coldest for any December on record. The upcoming weekend will be a rough one in the Twin Cities, with a low of around -15°F expected Saturday night and a high of just -5°F on Sunday. Neither would be a record, though: Minneapolis dipped to -24°F on December 18, 1983 (and -29°F the next night), with a high on the 18th of just -11°F. Other potential records and close-but-no-cigar forecasts:

Albany, NY, Fri. 12/16: forecast low -1°F (daily record -11°F, 1917)
Boston, MA, Fri. 12/16: forecast low 6°F (daily record 1°F, 1883)
International Falls, MN, Sun. 12/18: forecast low -22°F (daily record -36°F, 1983)
Detroit, MI, Mon. 12/19: forecast low -6°F (daily record -6°F, 1884)
Louisville, KY, Mon. 12/19: forecast low 15°F (daily record -5°F, 1884)

We’ll be back with a new post by Friday at the latest.

Bob Henson


Sea level pressures near the peak of the December 1983 cold wave, as mapped by the North American Regional Reanalysis. Image credit: Greg Carbin, NOAA.


Winter Weather

Hundreds of Scientists Rally in San Francisco to Stand Up For Science

By: Jeff Masters , 3:46 PM GMT on December 14, 2016

Over 26,000 earth scientists are gathered this week in San Francisco for the annual meeting of The American Geophysical Union—the world’s largest conference on climate change. During the noon lunch break on Tuesday, I took a break from the usual hard science presentations and participated in something scientists will have to increasingly engage in—activism to protect science from political interference. Hundreds of scientists from the meeting were joined by hundreds more concerned citizens from the Bay Area in a “Stand Up For Science” rally, organized by climatetruth.org and The Natural History Museum. The speakers, which included Penn State climate scientist Michael Mann, Harvard history of science professor Naomi Oreskes (author of the excellent book and movie, Merchants of Doubt), Peter Frumhoff of the Union of Concerned Scientists (target of subpoenas this year brought by the House Committee on Science, Space, and Technology), Leila Salazar at Amazon Watch, Andres Soto at Communities for a Better Environment, David Karabelnikoff at Idle No More Bay Area, and James Coleman, student fellow at Alliance for Climate Education. The speakers affirmed that:

- Climate change is a real, human-caused, and urgent threat.
- We must uphold the United States' commitment to the Paris Climate Agreement.
- We must protect scientific integrity in policymaking.
- We must protect government scientists from censorship or suppression.
- We must reduce carbon pollution and U.S. dependence on fossil fuels.
- We can make the U.S. a clean energy leader, and champion the just transition to a new energy era that works for all of us.


Figure 1. Penn State Climate scientist Michael Mann addresses a crowd of about 500 people at Tuesday’s Stand Up For Science rally in San Francisco.

Peter Frumhoff of the Union of Concerned Scientists urged all the scientists there to join in signing an open letter to Donald Trump, calling on the incoming Trump administration and 115th Congress to ensure that science continues to play a strong role in protecting public health and well-being. If you are a scientist and would like to add your name to the letter, whose signers include 22 Nobel prize winners, you can do so here.

The most effective speaker at the rally was Georgia Tech climate scientist Kim Cobb, who related her experience this year of scuba diving on Australia’s Great Barrier Reef and seeing it decimated by a massive coral bleaching episode due to record-warm ocean waters. She urged the scientists there to become activists—to get out of their comfortable chairs where they talk about data with colleagues, and help make a difference. “What are you waiting for?” she implored. “If we speak together, I am confident we can change the course of history.”

The rally closed with a few enthusiastic chants by the normally reserved scientists there:

Water is life!
Out of the labs and into the streets !
Stand up for science!

The rally was also covered by The San Francisco Chronicle. See if you can spot my bald spot in one of the photos in the article.

My related post: On Giving Tuesday, Support Increasingly Embattled Climate Scientists.

Note: The views expressed above are my own and not necessarily representative of The Weather Company or IBM.

Jeff Masters

Climate Change Politics Climate Change

2016 Holiday Shopping Guide for the Weather Enthusiast

By: Jeff Masters and Bob Henson , 5:26 PM GMT on December 12, 2016

Hunting for that special something for a budding meteorologist or a lifelong weather enthusiast? You can’t go wrong with an atmosphere-related gift. Below is the 2016 installment of our traditional holiday shopping guide.

Holiday books for the weather and climate science enthusiast

Jeff’s pick: “The Madhouse Effect: How Climate Change Denial Is Threatening Our Planet, Destroying Our Politics, and Driving Us Crazy”

If you're wondering why so many politicians and news sources deny that dangerous human-caused climate change is real, and you want a relatively short and easy-to-read summary of the issue, look no further than “The Madhouse Effect” (Columbia University Press, 2016), by Penn State climate scientist Dr. Michael Mann. Published in 2016, “The Madhouse Effect” is illustrated with about 50 cartoons by Pulitzer Prize-winning cartoonist Tom Toles of the Washington Post, whose cartoons manage to be hilarious and sobering at the same time. Dr. Mann is a leading climate scientist, and is also author of "The Hockey Stick and the Climate Wars", which I reviewed in 2012. The book is separated into eight sections:

Science: How it Works
Climate Change: The Basics
Why Should I Give a Damn
The Stages of Denial
The War on Climate Science
Hypocrisy--Thy Name is Climate Change Denial
Geoengineering, or “What Could Possibly Go Wrong?”
A Path Forward

The text is easy to understand--written at a level for anyone with a high school science education. Tom Toles’ excellent cartoons add some pizzaz, so that the book is not boring. At just 150 pages, “The Madhouse Effect” is of a very digestible length, and should take only two hours or so to peruse. The book concludes with words that are now far more timely than Mann and Toles could have known when the book was published earlier this year: ”This is our home. It’s time to start acting like it.” The paperback version of “Madhouse Effect” is $15.51 from Amazon.com.  I give "Madhouse Effect" five stars out of five. The book would be a nice companion to my recommendation from last year’s holiday gift guide, ”Dire Predictions: Understanding Climate Change -- The Visual Guide to the Findings of the IPCC,” by Dr. Mann and fellow Penn State professor Lee Kump, published in 2015.

Bob’s pick: “Hurricane Pioneer: Memoirs of Bob Simpson”

Few in the world of atmospheric science have enjoyed a career as varied, illustrious, and extended as the one carved out by Dr. Robert Simpson, who died in late 2014 at the age of 102. We’re lucky that Dr. Simpson took the time to document his busy life in detail, as told in “Hurricane Pioneer” (AMS Books, 2015).

It wasn’t obvious at first that Bob Simpson would devote much of his professional life to tropical cyclones. In fact, he spent the latter 1930s as a successful high school music and physics teacher in his native Texas, before taking a 67% pay cut to join the U.S. Weather Bureau in Brownsville as a novice observer. World War II opened big doors for Dr. Simpson, as he trained at the legendary University of Chicago Institute of Meteorology, then went on to work in the Miami Weather Bureau office with famed forecaster Grady Norton.

This memoir includes background on Dr. Simpson’s forays into early hurricane hunting and “piggyback” research, and on his tenure as the second director of the National Hurricane Center (though with so much to cover, the book seldom lingers on any one event or period). Even as his involvement in tropical meteorology blossomed, Dr. Simpson had a hand in other crucial developments, including a network of Texas radars that served as the prelude for the first national weather-radar network as well as the establishment of the Mauna Loa Observatory, now the world’s gold-standard location for tracking the buildup of carbon dioxide in the atmosphere.

Although there’s little meteorology in the first third of the book, we do learn how Dr. Simpson’s childhood in Corpus Christi, Texas, was shaped by the trauma of a deadly 1919 hurricane. There is plenty of insight on Dr. Simpson’s personal and professional relationships, including his 45-year marriage to Dr. Joanne Simpson, an eminent atmospheric scientist in her own right and the first woman to achieve a doctorate in meteorology. Dr. Simpson is candid about the downsides of his globetrotting career path, including an early divorce, and he closes the book with reflections on how his spiritual and scientific paths interrelated. Interestingly, the Saffir-Simpson Hurricane Wind Scale—perhaps his best-known achievement, created with civil engineer Herbert Saffir--gets only two paragraphs, including a self-deprecating comment from Dr. Simpson on the scale’s naming in 1975: “This designation was by committee action, not by our request, and a bit of an embarrassment to me.” Available from the AMS Bookstore for $25 ($20 for members and students), “Hurricane Pioneer” gets five stars for the gentle eloquence of its narrator and for its unique perspective on a 20th-century life in atmospheric science.

A Personal Weather Station: yes!
Every serious weather enthusiast deserves a Personal Weather Station (PWS) in their backyard! Not only can you enjoy seeing what the weather is in your backyard, you can share the data with everyone else on the Internet by uploading to the wunderground Personal Weather Station network, which boasts data from more than 200,000 stations. You don’t need to have a computer on all the time to collect the data and send it to the Internet--a WeatherBridge device will keep the data flowing to the Internet even when your computer is turned off. A full list of wunderground-compatible PWS models, software, and add-ons like the Ambient WeatherBridge is available from our Personal Weather Station buying guide page, including helpful background on how to choose among the possibilities based on your needs.

Jeff’s picks:

An economical PWS choice: Netatmo
The Netatmo Weather Monitor ($179) contains a unique set of sensors to monitor your indoor and outdoor living environment and wirelessly transmits all your data to your desktop or mobile device. Optional add-ons include a rain gauge ($79) and wind gauge ($99.99). The Netatmo app pulls your station’s indoor and outdoor measurements into clear and comprehensive dashboards, graphs, and notifications.

A mid-range PWS choice: Davis Vantage Vue
The Davis Vantage Vue + WeatherBridge Package is $625 from ambientweather.com. Combine the convenience of WeatherBridge with Davis Instruments' Vantage Vue™ station, which is fully featured, highly accurate and affordably priced.

A high-end PWS choice: Rainwise
I have had a Davis Vantage Pro2 in my backyard for the past eight years, and have been very happy with it, but I also recommend the RainWise Direct to Weather Underground Package, $999 from rainwise.com. The RainWise RapidFire™-enabled weather station doesn't need a PC to upload data to us, and with an ultra-fast refresh rate of every 3-5 seconds, new data is updated instantly.



Weather Underground T-shirts and hoodies
If you’ve ever craved the cool WU apparel featured on The Weather Channel’s #wutv program (6 - 8 PM EST weeknights), you can now share your WU fandom at a sweet discount. The Weather Underground store has an assortment of T-shirts and hoodies available for 10% off through January 1 when you use this promotion code: WUHOLIDAY10.

Connect your favorite services with IFTTT
Here’s a holiday gift for yourself, friends, and family that won’t cost a dime. Weather Underground is now the exclusive weather provider for IFTTT, a freely downloadable platform that allows apps and connected services to work together seamlessly. Applets within IFTTT call on various features of the apps you already use to create new capabilities. For example, each WU app already allows you to activate “push” notifications of severe weather alerts. Applets in IFTTT go even further: it can notify you if WU is predicting rain for your area tomorrow, or remind you to put on sunscreen whenever the UV index is high. There’s even the ability to call on localized sunset data from WU to automatically transition your home-based connected devices to nighttime mode (including Hue lights, Nest thermostats, and WeMo light switches). See the IFTTT weather page for many other nifty WU-related options, and learn more about the IFTTT-WU collaboration in a press release issued December 8 by The Weather Company.

This week we’re in San Francisco at the American Geophysical Union’s Fall Meeting, the world’s largest gathering of Earth and space scientists. We’re also keeping an eye on the cold wave to be reinforced through the week across much of the central and eastern U.S. We will be back with a new post by Wednesday at the latest.

Jeff Masters and Bob Henson



Book and Movie Reviews

Autumn 2016: Warmest in U.S. Weather History

By: Bob Henson , 6:10 PM GMT on December 07, 2016

The autumn of 2016 was the warmest ever observed in records going back to 1895 for the 48 contiguous U.S. states, according to data released on Wednesday by NOAA’s National Centers for Environmental Information (NCEI). The nation’s average September-to-November temperature of 57.63°F was a full 1.05°F above the previous autumn record, set way back in 1963, and it was 4.08°F above the 20th-century average (see Figure 1). The record-setting margin of more than 1°F is a hefty one for a temperature record that spans an entire season and a landmass as large as the 48 contiguous states. For comparison, the second, third, fourth, fifth, sixth, and seventh-warmest U.S. autumns are all clustered within 1°F of each other, as are the six coldest autumns on record.

Pushing this past autumn to the top of the temperature pack were the third-warmest October and third-warmest November on record, along with the ninth-warmest September. Eight states along a swath from New Mexico to Michigan saw their warmest autumn on record, and every contiguous state except for California, Nevada, Oregon, and Washington had a top-ten warmest autumn (see Figure 2).


Figure 1. Autumn 2016 was by far the warmest on record for the contiguous United States. Image credit: NOAA/NCEI.


Figure 2. Statewide rankings for average temperature during September - November 2016, as compared to each September - November period since 1895. Darker shades of orange indicate higher rankings for warmth, with 1 denoting the coldest month on record and 122 the warmest. Image credit: NOAA/NCEI.

Record highs outpace record lows in November by an unprecedented margin
Although it wasn’t the warmest November on record, last month transcended all other months in modern U.S. weather history by the outsized presence of record highs to record lows. According to preliminary NOAA data compiled through Wednesday, November saw 4544 daily record highs set or tied, and just 94 daily record lows set or tied--a ratio of more than 48 to 1! This is the largest such ratio for any month in U.S. data going back to the 1920s, according to independent meteorologist Guy Walton (@climateguyw), who has tracked U.S. records for many years. Because many U.S. reporting stations came on line in the 1890s, the occurrence of records did not stabilize until around the 1920s.

The total of 94 daily record lows in November is remarkably sparse--the lowest value for any month since September 1922. In general, it’s best to use warm-to-cold ratios rather than comparing the raw number of records over time, observed Deke Arndt, the chief of NOAA/NCEI’s Climate Monitoring Branch. “Because the number and lifetimes of weather stations has varied over time, comparing raw numbers of records doesn't completely capture the signal. Using a ratio of warm-to-cold records helps account for these effects,” Arndt told Mashable’s Andrew Freedman. Each decade since the 1980s has seen more daily record highs than lows, with the ratio increasing to nearly two-to-one during the 2000s and just over two-to-one for the 2010s through November 2016.

Although 2016 is running just behind 2012 as the warmest year in U.S. records thus far, the widespread chill expected to continue through at least mid-December has a good chance of keeping this year from outpacing 2012.


Figure 3. Statewide rankings for average precipitation during September - November 2016, as compared to each September - November period since 1895. Darker shades of green indicate higher rankings for moisture, with 1 denoting the driest month on record and 122 the wettest. Image credit: NOAA/NCEI.

Big regional contrasts in precipitation
November was the 25th driest on record, with the average 48-state precipitation total of 1.73” a half inch below the 20th-century mean of 2.23”. For the autumn as a whole, precipitation came in very close to the long-term mean when averaged across the 48 contiguous states, with 2016 placing the 65th wettest autumn in 122 years of data. However, that “normal” value obscures some major regional differences, as seen in Figure 3 (above). It was the wettest autumn on record in Washington, as a powerful Pacific jet brought vast amounts of moisture into the Pacific Northwest. States from California to the upper Midwest were all much wetter than average this autumn. The jet stream largely passed Colorado’s mountains, though, leaving the state with its eighth driest autumn on record.

The other major wet zone this autumn was along the Southeast coast, as Hurricane Matthew dumped enormous amounts of rain and set a number of local rainfall and storm-surge records. The resulting floods were catastrophic across parts of inland North Carolina, where the rains pushed rivers to record crests and flooded an estimated 100,000 structures, producing at least $1.5 billion in damage. Of the 49 deaths attributed to Matthew, 28 occurred in North Carolina. Both North and South Carolina came in with their 19th wettest autumns on record, although those values are skewed somewhat by the failure of Matthew to drench western parts of those states and by the largely dry weather before and after Matthew.


Figure 4. A man pumps floodwaters from the inside of a business on October 15, 2016, in Lumberton, NC. The Lumberton area was especially hard hit by torrential rains and flooding produced by the passage of Hurricane Matthew near the North Carolina coast. Image credit: Sean Rayford/Getty Images.

Drought and fire take their toll in the Southeast
A vicious drought sank its claws deeper into parts of the South this autumn, with Louisiana, Mississippi, Alabama, Tennessee, and Kentucky all seeing a top-ten driest autumn. Combined with near-record warmth, the dryness primed forests across the central and southern Appalachians for widespread wildfires that culminated in deadly disaster in the Gatlinburg, TN, area last month. The death toll in Gatlinburg now stands at 14, with more than 1400 structures damaged or destroyed and a damage toll estimated at more than $100 million by the insurance broker Aon Benfield. As of December 1, most of Mississippi, Alabama, Georgia, and Tennessee were in extreme or exceptional drought on the weekly U.S. Drought Monitor. Generous rains of 1” - 3” across much of this region over the past week will help put a dent in the drought, although much more moisture is needed to recoup widespread annual deficits on the order of 12” to 20” (even more in some locations).

We’ll be back with a new post by Friday at the latest. Note: because of required maintenance, this blog and our other WunderBlogs and WunderPhotos will be offline for about 4 - 6 hours beginning at 6 PM PST (9 PM EST) Wednesday night.

Bob Henson


Figure 5. Smoke rises from destroyed buildings Tuesday, Nov. 29, 2016, at the Westgate Smoky Mountain Resort & Spa above Gatlinburg, Tenn., the day after a wildfire. Image credit: Paul Efird/Knoxville News Sentinel via AP.

Climate Summaries

Climate Change Won’t Stop in 2016, Despite Misleading Reports

By: Bob Henson and Jeff Masters , 2:52 PM GMT on December 06, 2016

With just three years left to go, it’s virtually certain that the 2010s will be warmer than any decade on record, barring a massive volcanic eruption. As greenhouse gases produced by human activity continue to build up in the atmosphere, it’s also a very good bet--again barring a volcanic or geopolitical cataclysm--that the 2020s will be warmer than the 2010s. You wouldn’t know about these perfectly reasonable, science-based inferences if all you had to go by was this article published by Breitbart.com on November 30: “Global Temperatures Plunge. Icy Silence from Climate Alarmists.” The article includes this statement: “The last three years may eventually come to be seen as the final death rattle of the global warming scare.”

Along with its presence on the high-profile Breitbart site, this article drew even more attention after a link to it was retweeted by the U.S. House Committee on Science, Space, and Technology. Fortunately, the article has been effectively rebutted by several excellent bloggers (see links below). Though we’d prefer to focus on our usual coverage of weather and climate science, in this case we felt it was important to add our two cents—especially because a video clip from weather.com (“La Niña in Pacific Affects Weather in New England”) was prominently featured at the top of the Breitbart article. Breitbart had the legal right to use this clip as part of a content-sharing agreement, but there should be no assumption that The Weather Company endorses the article associated with it.

A plump cherry, carefully picked
The Breitbart article is a prime example of cherry picking: pulling a single item out of context in order to build a misleading case. The article draws heavily on a (U.K.) Daily Mail article from November 26 by David Rose titled “Stunning new data indicates El Niño drove record highs in global temperatures suggesting rise may not be down to man-made emissions.” (In the U.K., the phrase “down to” is a synonym for “attributable to”.) The plucked cherry, in this case, is the fact that satellite-based estimates of temperature in the lower several kilometers of the atmosphere over Earth’s land areas have decreased from early 2016 to late 2016 (a graphic in the Daily Mail attributed only to “NASA satellites” shows this drop as being more than 1.0°C). The article implies that global temperatures may soon return to levels seen in the late 1990s.

Here are a few points crucial for putting this isolated factoid into proper context:

--On time scales of a few months, temperatures rise and fall more quickly over land than over the ocean (as acknowledged by Rose). The ocean takes up about 70% of Earth’s surface, so land-only temperatures are an incomplete measure of global climate change. The land-plus-ocean data for the lower atmosphere published by Dr. Roy Spencer (University of Alabama in Huntsville, UAH) shows a cooling of about 0.5°C earlier this year, or only about half of the 1.0°C claimed for the land-only dataset. Despite this, the year 2016 is on pace to be the warmest year on record in the UAH lower atmosphere dataset.

--Satellite-based temperature estimates for the lower atmosphere are not the same as temperature trends measured at Earth’s surface, where people live. Satellite-derived estimates of the lower atmosphere air temperatures are much more sensitive to El Niño, the large-scale natural warming that occurs in Eastern Pacific waters every 2 - 7 years. When a strong El Niño event ends, as occurred earlier this year, we expect to see a substantial drop in satellite-based temperature estimates for the lower atmosphere—and just a slight drop in temperatures measured by weather stations on Earth’s surface, as was observed.

--Three different groups publish satellite-based temperature estimates for the lower atmosphere: UAH, RSS, and NOAA’s STAR. The Breitbart and Daily News articles picked the one with the largest drop, from RSS. The other two data sets show no similar dramatic drop, just the sort of normal decline one would expect to see after the end of a strong El Niño event. Recently, RSS found an error in their lower tropospheric temperature estimates which has yet to be corrected. They state on their website that the data suffers problems “with the adjustment for drifting measurement times” and “should be used with caution”. Ironically, the RSS data for the month of November, which was released on Friday after the Breitbart and Daily News articles were published, shows a substantial uptick in satellite-based temperature estimates for the lower atmosphere over land. Notably, the combined land plus ocean numbers from both RSS and UAH for November showed Earth’s warmest November on record!


Figure 1. Global surface temperature (including both ocean and land areas) for the 12-month-long November-to-October periods from 1880 to present. Image credit: NOAA/NCEI.

A pointless argument: Was it El Niño or climate change that led to the record warmth in 2015-16?
Much of the Breitbart and Daily News articles focused on the idea that the two-year El Niño event that ended this year may have been entirely responsible for the record-warm global readings of 2015 and 2016. It is well established that El Niño and La Niña produce spikes and dips in global temperature, typically lasting a year or two, atop the long-term trend of warming from increasing human-produced greenhouse gases. It’s apparent from Figure 2 below (featured at the indispensable website skepticalscience.com) that the spikes and dips from typical El Niño and La Niña events average about 0.1°C each, and roughly 0.2°C to 0.3°C for the very biggest events. In comparison, global surface temperatures have risen more than 0.6°C since the mid-20th century, and close to 1.0°C over the last 100 years. Thus, the bulk of the unusual warmth of a year like 2016, compared to readings a century ago, is the result of long-term warming. Put another way, the spikes that set record global highs are typically related to El Niño, but these spikes couldn’t set global highs without resting atop the rock-solid foundation of long-term warming. Otherwise, we’d see strong La Niña events setting global record lows--and this clearly isn’t happening. If we remove the El Niño spike, 2016 (to date) is still the hottest year on record and 2015 is the second hottest year on record (see the excellent analysis on this by Zeke Hausfather, a climate scientist and energy systems analyst at Berkeley Earth.)

Assuming that 2016 sets a new global surface temperature record (a virtual certainty), it will actually be the third record-warm year in a row. The most recent El Niño event did not begin until the last quarter of 2014, so most of the record warmth of that year cannot be attributed to El Niño at all. It’s also important not to confuse the multi-decadal ups and downs evident in Figure 1 with the longer-term warming trend caused by greenhouse gases. During periods when El Niño events are more common than La Nina events, more heat is being sent from ocean to atmosphere and global temperatures can rise dramatically, as was the case during most of the 1980s and 1990s. Similarly, when La Niña is more common than El Niño, more heat is being stored in the oceans and the global atmosphere may warm a bit more slowly, as was the case from about 1998 to 2013. (See our 2015 post on the Pacific Decadal Oscillation for more background.) These shifts play out atop the human-produced warming trend, which is forced by greenhouse gases accumulating in our atmosphere at greater and greater concentrations every year.


Figure 2. Global surface temperature trends for the period 1966 - 2015 analyzed for El Niño years (red boxes), La Niña years (blue boxes), and neutral years (black boxes), along with volcanic years (gold triangles). The three trend lines show that global temperature has been rising at a fairly consistent rate of about 0.15 - 0.17°C (0.27 - 0.31°F) per decade once La Niña and El Niño departures are factored out. Image credit: skepticalscience.com; data from Berkeley Earth.

Artificial debates interfere with the discussions we really need to have
There remains a spectrum of confidence on how climate change will affect various types of extreme weather. The research is more mature in some areas than in others, as explained in a major 2016 report from the National Academies. Scientific debate in this area is real and perfectly legitimate. Likewise, how we respond to climate change is a matter of public policy, one that demands healthy debate and engagement from citizens and political leaders. It’s something else entirely to foster suspicion about the very bedrock of climate change science, which is based on thousands of peer-reviewed studies and accepted by every major scientific organization on Earth. Human-produced greenhouse gases are causing the Earth system to warm, and this trend will continue, along with shorter-term ups and downs. There are too many important debates and decisions ahead of us to waste time on artificial ones.

Bob Henson and Jeff Masters
Note: Our views are our own and not necessarily representative of The Weather Company or IBM.

Links
You can see line-by-line critiques of the Daily Mail article from climate scientists at the Climate Feedback website.

“We’ve Been Waiting for this Whopper, and It Has Arrived!”
Dan Satterfield, AGU Blogosphere

“How Stupid Does David Rose Think You Are?”
Tamino, Open Mind blog

”U.S. House Science Committee tweets Breitbart climate misinformation”
Scott Johnson, Ars Technica

“Earth’s temperature has not plunged at record clip and nationwide record cold not coming”
Capital Weather Gang (Jason Samenow)

Climate Change Politics Climate Change

U.S. Weather Returns to Its Climatological Senses, and Then Some

By: Bob Henson , 3:44 PM GMT on December 05, 2016

After a markedly mild November marked by thousands of daily record highs and less than 100 record daily lows (more on that in our upcoming monthly roundup), it will feel much more like December across the bulk of the contiguous U.S. over the next couple of weeks. Some locations may see their coldest weather in years as a series of Arctic high pressure cells swing through western Canada and southward across all but the Desert Southwest.

A sneak preview of the wintry weather to come hit parts of the Midwest on Sunday, when an anticipated light snow turned out to be a more efficient producer than expected. The 6.4” of snow at Chicago’s O’Hare International Airport was the city’s heaviest December snowfall since 2005. It was also more snow than Chicago obtained in December 2014 and 2015 combined (4.5”). Snowfall records for December 4 were set at Chicago as well as at Moline, IL (7.8”) and Madison, WI (5.7”). This fast-moving but mostly light snow shield will scoot across New England on Monday.


Figure 1. The first snow of the season descended on Sturgeon Bay, Wisconsin, on Sunday, December 4, 2016. Image credit: wunderphotographer lablover47.

A brief warmup for much of the central U.S. on Monday will be followed by the first of several Arctic blasts, each more intense than the last. The first front will push from the Northern Rockies on Monday into the Midwest on Tuesday and the Northeast by Wednesday. A stronger reinforcing shot will kick in later in the week, with that front pushing all the way through the Gulf of Mexico and across Florida by the weekend. Most of the Plains and South will see temperatures as much as 20 - 25°F below average late this week. A widespread, crippling snowstorm isn’t expected, though the Front Range of Colorado may get a few inches by Wednesday. Favored lake-effect-snow regions near the Great Lakes could get hammered late this week as the frigid air approaches from a favorable direction and passes over waters that are running 5°F or more above average in many locations.


Figure 2. Low temperatures projected by the GFS model run from 00Z Monday show that temperatures at 12Z Friday, December 9, 2016 (6 AM CST/7AM EST) may dip below freezing as far south as southern Louisiana and the northwest Florida panhandle. Image credit: tropicaltidbits.com.

More to come next week?
In the longer range, the GFS and ECMWF models indicate that the mid-level polar vortex may split in two next week, with one lobe shifting into Canada, the other perched atop western Russia, and a strong ridge extending from the North Pacific into the Arctic. If this pattern materializes, especially as depicted by the GFS, it would be conducive for additional Arctic surges into the contiguous U.S., likely bringing the coldest air of the year so far. Many record lows in December were set decades ago, during a notably cooler U.S. climate, so it’s typically difficult to match those readings without a truly intense cold shot. Still, it wouldn’t be surprising to see a good number of daily record lows (and record-low maxima) challenged if not broken next week should the projected pattern take hold.

Bob Henson

Winter Weather

More Tornadoes in the Biggest U.S. Outbreaks--for an Unexpected Reason

By: Bob Henson , 5:40 PM GMT on December 02, 2016

The largest U.S. tornado outbreaks have been spitting out an ever-increasing number of twisters, according to a study published Thursday in the journal Science. The new paper, led by Michael Tippett (Columbia University), reinforces prior work showing that U.S. twisters are increasingly concentrated in big outbreaks, with the quiet periods becoming even quieter. Tippett and colleagues also threw in a noteworthy curve ball. It appears the growing number of tornadoes in the most extreme outbreaks is not because of greater instability--something that long-term climate change is expected to produce--but instead as a result of increased storm-relative helicity, one measure of the “spin” produced by vertical wind shear that translates into rotation within tornadic supercell thunderstorms. As the paper puts it, “Tornado outbreaks with many tornadoes are increasingly frequent, but lack the presently understood meteorological signature of global warming.”


Figure 1. This EF2 tornado south of Dodge City, Kansas, on May 24 was one of 87 twisters observed in a five-day outbreak from May 22 to 26, 2016. Image credit: Bob Henson.

Signs from the worst of the worst
The new study examines tornado outbreaks for the period 1965 - 2015 using extreme value analysis. This is a technique especially well suited for delving into very infrequent events, where the outliers of a “long-tail” distribution are the topic of keenest interest. The authors limited their scope to tornadoes of at least F1/EF1 on the Fujita/enhanced Fujita scales, given that the vast increase in the number of people spotting, chasing, or otherwise finding twisters has artificially boosted the number of weak tornadoes (F0/EF0). The trends in outbreaks emerged most clearly when looking at those with at least 12 tornadoes, and when placing those 435 outbreaks into five percentile brackets (e.g., dividing each year’s outbreaks into five groups based on the number of tornadoes per outbreak). This revealed a significant increase in the number of tornadoes per outbreak, especially for the largest events. From the late 1960s to the early 2010s, the number of tornadoes per outbreak in the top fifth of outbreaks rose from around 20 to more than 35. Likewise, the size of the largest outbreak one might expect every five years roughly doubled, from 40 in 1965 to nearly 80 in 2015.

Since there hasn’t been any significant growth in the number of outbreaks themselves, or in reliable tornado reports, it appears that tornado production is increasingly concentrated in the biggest outbreaks, with fewer twisters in between. It’s a conclusion reached in recent years through work by Harold Brooks (National Severe Storms Laboratory) and others. The 2010s have featured increasingly wild swings between hyperactive and relatively tranquil periods. One example: for the period from April 15 to July 31, the U.S. lurched from a near-record total in 2011 (including the catastrophic Super Outbreak and the horrific Joplin tornado) to a record-low total in 2012. Early 2015 was also remarkably quiet on the severe weather front. And the latter half of drought-ridden 2016 has pushed the year’s tornado total close to record lows, even when we factor in the spate of more than 50 twisters reported on Tuesday and Wednesday that led to at least 5 deaths.


Figure 2. Marcia Remick, of Rosalie, Alabama, digs through the debris and aftermath of a damaging tornado on Thursday, December 1, 2016. The EF3 tornado carved a 13-mile path through the area on Wednesday, killing 3 people. Image credit: AP Photo/Brynn Anderson.

Shear bemusement
What’s behind the clustering of tornadoes into ever-more-extreme outbreaks? That’s the most intriguing part of the new paper. It’s long been expected that human-produced climate change would lead to an increase in warm, moist conditions at lower levels of the atmosphere as compared to upper levels. This instability is often expressed in the form of CAPE: convective available potential energy. Global climate models also tend to project a decrease in vertical wind shear over the nation.

Putting two and two together, one might expect that more overall CAPE and less overall shear would work against any increase in tornadoes--but that’s not necessarily the case, according to a landmark study published in 2013 and led by Noah Diffenbaugh (Stanford University). That paper, which drew on the most recent suite of global climate modeling in support of the IPCC process, found that projected reductions in wind shear tend to be concentrated in days that aren’t very unstable to begin with, whereas there may actually be an increase in days with enough CAPE and enough shear to produce tornadic storms. “This is the key result of our 2013 paper: changes in the mean aren’t indicative of the changes in the occurrence of extremes,” Diffenbaugh told me.

What Tippett and colleagues found in looking at outbreaks from the last 50 years is something quite different than the scenario of future tornado activity from Diffenbaugh and colleagues. It turns out that CAPE hasn’t yet increased significantly in the extreme-outbreak settings, but wind shear in these settings, as measured by storm-relative helicity (SRH) in the lowest 3 kilometers of the atmosphere, has increased, with the biggest increases found for the largest outbreaks. “This is an unexpected finding,” Tippett said. “The fact that we don’t see the presently understood meteorological signature of global warming in changing outbreak statistics leaves two possibilities: either the recent increases are not due to a warming climate, or a warming climate has implications for tornado activity that we don’t understand.”

There’s no immediate explanation for why SRH during outbreaks has been on the increase. Could it be related to some form of multidecadal climate variability? The authors didn’t find any strong relationship to signals such as the Atlantic Multidecadal Oscillation, the Pacific Decadal Oscillation, or U.S. temperature trends. “I’m not convinced it's [because of] long-term climate oscillation,” Harold Brooks told me. “I think SRH could be changing because of global warming in ways we don't understand yet.” Tippett said: “We’re definitely raising some questions without answers yet. If global warming is changing tornado activity, then we might expect to see either continued increases in the number of tornadoes per outbreak or at least no return to earlier levels. On the other hand, if multidecadal variability, anthropogenic or natural, is responsible, then a return toward earlier levels might be possible.”

Is it too early to detect a human-produced signal in tornado outbreaks?
Although it might seem so at first glance, the new paper isn’t really in conflict with the longer-term projections from the work of Diffenbaugh and colleagues. The climate models analyzed by that group don’t show an increase in tornado-favorable environments kicking in strongly until decades from now, assuming that global temperatures will by then reach the commonly cited (and feared) 2°C threshold over preindustrial values. “We see some indication of emergence between the present and the 2°C level of global warming, particularly in the spring over the eastern U.S.,” said Diffenbaugh. “It’s really after 2°C that we see very clear emergence across the climate models and in multiple seasons.” For now, he added, it’s important to clearly determine exactly what changes in tornado activity have occurred across recent decades, especially given the complexities of the data. “I think [the Tippett et al. paper] is an important step in this line of research.”

We’ll be back with our next post on Monday.  Have a great weekend, everyone!

Bob Henson


Figure 3. Cunningham Park in Joplin, Missouri, has become a memorial to victims of the tornado of May 22, 2011, which killed more than 150 people in Joplin. The memorial includes a large ring (foreground) celebrating the human spirit. In the background of this photo from April 21, 2012, is St. John’s Regional Medical Center, which was severely damaged by the tornado and eventually demolished. St. John’s reopened in 2015 as Mercy Hospital in a new facility four times larger than its predecessor. Image credit: Stephanie Himango/NBC/NBC NewsWire via Getty Images.


Tornado


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

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