Category 6™

Wild weather rings out the old year: tornado kills three in Arkansas

By: JeffMasters, 4:31 PM GMT on December 31, 2010

The wild weather year of 2010 is closing out in dramatic fashion in the U.S., where a powerful storm system moving through the center of the country has spawned a tornado that killed three people in Northwest Arkansas early this morning. According to media reports, the tornado swept through Washington County in Northwest Arkansas between 6am - 6:10am CST this morning, killing three, injuring many more, and causing significant damage throughout the western portion of the county. Emergency responders are having difficulty reaching the damaged areas due to downed power lines, and power is out over most of the county. The supercell thunderstorm responsible for the tornado has maintained its identify for more than four hours along a path more than 200 miles long this morning, a unusually long time for a thunderstorm to maintain its identity. As of 11am EST, the tornado warnings for the thunderstorm has been issued for eastern Missouri, and the storm is headed towards St. Louis. Visit our interactive tornado page and severe weather page to monitor this ongoing severe weather situation. Today's three tornado deaths brought this year's tornado death toll to 39. This is higher than last year's record-low total of 21 tornado deaths, but much lower the 3-year average of 76 tornado deaths per year.

Figure 1. Radar reflectivity (top) and Doppler velocity image (bottom) of the supercell thunderstorm that hit northwestern Arkansas this moring, killing three people in the town of Cincinnati.

Meanwhile, the storm responsible for the deadly tornado is also bringing a dangerous winter storm to the West and Midwest. Blizzard warnings are in effect for southeastern Wyoming, western Nebraska, the Dakotas, and western Minnesota. According to the latest NOAA Storm Summary, the storm has dumped over 30 inches of snow in Colorado at Coal Bank Pass and Skyway, and at Sage Creek Basin in Wyoming. Some other selected snowfall amounts as of 10am EST:

Idaho City, ID: 36.0"
Soda Springs, CA: 36.0"
Deer Valley Daly West, UT: 33.0"
Williams, AZ: 29.5"
Sheep Canyon, WA: 29.0"
Missoula, MT: 24.0"
Flagstaff, AZ: 22.0"
Boise, ID: 20.0"
Green Mountain, NV: 20.0"
Durango, CO: 20.1"
Jackson, WY: 17.3"
Los Alamos, NM: 17.0"
Creighton, SD: 12.0"
Fergus Fall, MN: 11.0"
Williston, ND: 7.1"

The storm also brought very heavy rains in excess of two inches to portions of Arizona, Missouri, and Arkansas, with amounts in excess of four inches reported in California and Oregon. The storm will intensify and move northeastwards into Canada north of Minnesota tonight, bringing an additional 6 - 12 inches of snow to the warned areas.

Have a Happy New Year's everyone, and I'm hoping 2011 brings us a little less in the way of wild weather!

Jeff Masters


Unprecedented flooding hits Australia's Queensland

By: JeffMasters, 10:57 PM GMT on December 29, 2010

Unprecedented flooding has hit the northeast Australian state of Queensland, thanks to a week and a half of torrential rains and the landfall of Tropical Cyclone Tasha on Christmas Day. Australian Prime Minister Julia Gillard stated yesterday, "Some communities are seeing flood waters higher than they've seen in decades, and for some communities flood waters have never reached these levels before [in] the time that we have been recording floods." The worst flooding occurred where Tropical Cyclone Tasha made landfall on Christmas Day. Though Tasha was a minimal tropical storm with 40 mph winds and lasted less than a day, the cyclone dumped very heavy rains of 8 - 16 inches (about 200 - 400 mm) on a region that was already waterlogged from months of heavy rains. According to the National Climatic Data Center, springtime in Australia (September - November) had precipitation 125% of normal--the wettest spring in the country since records began 111 years ago. Some sections of coastal Queensland received over 4 feet (1200 mm) of rain from September through November. Rainfall in Australia in December may also set a record for rainiest December. The heavy rains are due, in part, to the moderate to strong La Niña event that has been in place since July. While the rains have eased over Queensland over the past few days, some rivers will not reach peak flood stage until Friday. Approximately 1000 people have been evacuated from the affected area so far.

Figure 1. Rainfall in Queensland, Australia for the 7-day period ending December 29, 2010. Image credit: Australian Bureau of Meteorology.

Figure 2. Radar image of Tropical Cyclone Tasha as it moved inland over Queensland, Australia on Christmas Day (local time.) Image credit: Australian Bureau of Meteorology.

Figure 3. River conditions in Queensland as of 8:30am local time on December 30, 2010. Image credit: Australian Bureau of Meteorology.

Flood warnings are in effect for over twelve rivers, and the flooding has closed approximately 300 roads across Queensland, including two major highways into the capital of Brisbane. Evacuations are underway in Rockhampton, a city of 50,000 people on the coast. Damage to infrastructure in Australia has been estimated at over $1 billion by the government, and economists have estimated the Australian economy will suffer an additional $6 billion in damage over the coming months due to reduced exports, according to insurance company AIR Worldwide. Queensland is Australia's top coal-producing state, and coal mining and delivery operations are being severely hampered by the flooding. Damage to agriculture is curently estimated at $400 million, and is expected to rise.

Flooding woes hit New Zealand
Wild weather has also hit New Zealand this week. Golden Bay on the northern end of the South Island of New Zealand had its worst floods in 150 years this week, thanks to torrential rains that dropped up to 13.2 inches (337.5 mm) in just 24 hours on Monday at one mountain location.

Figure 4. Two webcam views of the Motueka River in New Zealand taken five hours apart on December 28, 2010, showing the dramatic rise in the river due to flooding rains. Image credit: Tasman District Council. Screen shots kindly sent to me by Matt Johnson.

Jeff Masters


Northeast U.S. digs out from yet another history-making snowstorm

By: JeffMasters, 4:53 PM GMT on December 28, 2010

The remarkable Post-Christmas blizzard of 2010 has ended for the United States, as the storm has trekked northeastward into Canada. The blizzard dropped epic amounts of snow during its rampage up the U.S. Northeast coast Sunday and Monday, with an incredible 32" falling in Rahway, New Jersey, about 15 miles southwest of New York City. The highest populated areas of New Jersey received over two feet of snow, including the Newark Airport, which received 24.1". Snowfall amounts were slightly lower across New York City. The blizzard of 2010 dumped 20.0" inches on New York City's Central Park, making it the 6th largest snowstorm for the city in recorded history, and the second top-ten snowstorm this year.

Figure 1. Scene from Brooklyn, New York after the Post-Christmas blizzard of 2010. Image credit: Wunderphotographer AK2NY.

Remarkably, New York City has had four of its top-ten snowfalls in the past decade (highlighted in the list below.) According to the National Weather Service, the top ten snowstorms on record for New York City's Central Park since 1869 should now read:

1) 26.9" Feb 11-12, 2006
2) 26.4" Dec 26-27, 1947
3) 21.0" Mar 12-14, 1888
4) 20.8" Feb 25-26, 2010
5) 20.2" Jan 7-8, 1996
6) 20.0" Dec 26-27, 2010
7) 19.8" Feb 16-17, 2003
8) 18.1" Mar 7-8, 1941
9) 17.7" Feb 5-7, 1978
10) 17.6" Feb 11-12, 1983

Newark's 24.2" was one of that city's top-ten snowstorms of all-time, and the 20.1" that fell on Atlantic City, NJ was the city's second largest snowfall in history. Atlantic City's three biggest snowstorms have all occurred in the past ten years:

1) 21.6" Feb 15-18, 2003
2) 20.1" Dec 26-27, 2010
3) 18.2" Feb 5-6, 2010

Philadelphia, PA picked up 12.4", the city's fourth one-foot plus snowstorm in just over a year--a remarkable string of storms, considering the city has had just 24 such snowfalls in history, since 1884. According to, the latest snowstorm brought Philadelphia's 2010 snowfall for the calendar year to 67.3", breaking the mark for snowiest year ever (previous record: 57.0" in 1978.)

The 18.2" that fell at Boston's Logan International Airport made the storm Boston's 8th biggest in history:

1) 27.6" Feb 17-18, 2003
2) 27.1" Feb 6-7, 1978
3) 26.3" Feb 24-28, 1969
4) 25.4" Apr 1, 1997
5) 19.8" Mar 3-5, 1960
6) 19.4" Feb 16-17, 1958
7) 18.7" Feb 8-10, 1994
8) 18.2" Dec 26-27, 2010
8) 18.2" Jan 7-8, 1996
10) 17.3" Feb 5-7, 1920

Some selected city snowfall amounts for the December 26-27, 2010 storm:

Rahway, NJ 32.0"
Great Kills, NY 29.0"
Piermont, NH 25.0"
Newark, NJ 24.2"
Landgrove, VT 21.0"
Atlantic City, NJ 20.1"
NYC Central Park, NY 20.0"
Boston, MA 18.2"
Ocean City, MD 13.5"
Philadelphia, PA 12.4"
East Providence, RI 10.0"
Danbury, CT 11.1"
Augusta, ME 15.0"
Dover, DE 9.0"
Asheville, NC 9.0"
Bridgeport, CT 8.0"
Huntsville, AL 6.0"
Chattanooga, TN 3.0"

There's a great 40-second time-lapse video of 32 inches of snow accumulating at Belmar, NJ.

Figure 2. The annual average number of snowstorms with a 6 inch (15.2 cm) or greater accumulation, from the years 1901 - 2001. A value of 0.1 means an average of one 6+ inch snowstorm every ten years. Image credit: Changnon, S.A., D. Changnon, and T.R. Karl, 2006, Temporal and Spatial Characteristics of Snowstorms in the Contiguous United States, J. Applied Meteorology and Climatology, 45, 8, pp. 1141-1155, DOI: 10.1175/JAM2395.1.

An unusual number of top-ten snowstorms for the Northeast in recent years
The Northeast has seen an inordinate number of top-ten snowstorms in the past ten years, raising the question of whether this is due to random chance or a change in the climate. A study by Houston and Changnon (2009) on the top ten heaviest snows on record for each of 121 major U.S. cities showed no upward or downward trend in these very heaviest snowstorms during the period 1948 - 2001. It would be interesting to see if they repeated their study using data from the past decade if the answer would change. As I stated in my blog post, The United States of Snow in February, bigger snowstorms are not an indication that global warming is not occurring. The old adage, "it's too cold to snow", has some truth to it, and there is research supporting the idea that the average climate in the U.S. is colder than optimal to support the heaviest snowstorms. For example, Changnon et al. (2006) found that for the contiguous U.S. between 1900 - 2001, 61% - 80% of all heavy snowstorms of 6+ inches occurred during winters with above normal temperatures. The authors also found that 61% - 85% of all heavy snowstorms of 6+ inches occurred during winters that were wetter than average. The authors conclude, "a future with wetter and warmer winters, which is one outcome expected (National Assessment Synthesis Team 2001), will bring more heavy snowstorms of 6+ inches than in 1901 - 2000." The authors found that over the U.S. as a whole, there had been a slight but significant increase in heavy snowstorms of 6+ inches than in 1901 - 2000. If the climate continues to warm, we should expect an increase in heavy snow events for a few decades, until the climate grows so warm that we pass the point where winter temperatures are at the optimum for heavy snow events.

I've done some other posts of interest I've done on snow and climate change over the past year:

Hot Arctic-Cold Continents Pattern is back (December 2010)
The future of intense winter storms (March 2010)
Heavy snowfall in a warming world (February 2010)

Jeff Masters

Winter Weather

Mighty Post-Christmas Nor'easter wallops the Northeast U.S.

By: JeffMasters, 3:07 PM GMT on December 27, 2010

A major blizzard continues to pound New England with heavy snow and winds gusting to near hurricane force as the 976 mb low tracks slowly northeastward into the Gulf of Maine. The snow has mostly ended across New York City and the mid-Atlantic, where snowfall rates as high as 3 - 4 inches per hour occurred during "thundersnow" snow squalls at the peak of the storm late last night and early this morning. At the height of the storm, blizzard warnings were in effect for the entire U.S. coast from Maryland to Maine. The heaviest snows fell about 50 miles to the west and north of New York City. Lyndhurst, New Jersey, located about 15 miles northwest of New York City, got 29 inches, and several nearby towns also reported snows in excess of 24 inches. Though the snow has mostly ended in these regions, strong winds will continue through the early afternoon, creating blizzard conditions in blowing snow.

Figure 1. Satellite image from 8am EST December 27 of the Post-Christmas Blizzard of 2010 over New England. Image credit: NASA/Goddard Space Flight Center.

The blizzard is in full swing across much of Massachusetts, Rhode Island, Connecticut, New Hampshire, and Maine, where snowfall rates of 1 - 2 inches per hours are common in heavy snow bands, with high winds creating blizzard conditions. The strongest wind gust from the mighty blizzard was 80mph, measured at Wellfleet on Cape Cod at 10:52pm last night. Wind gusts of 50 - 60 mph have been common along most of the coast of Connecticut, Rhode Island, and Southeast Massachusetts. The storm's strong northeast winds whipped up a storm surge of 2 - 3 feet that affected the coast just north of Boston, and in Central Long Island Sound, during the high tide cycle at 3am this morning. Moderate flooding that shut many roads occurred, and some damage to buildings probably resulted. The flooding danger for Massachusetts and Long Island Sound is now past, as the storm moves into Maine and Canada.

Snowfall amounts at major cities for the December 26-27, 2010 storm, as of 8am EST:

Newark, NJ 20.0"
Atlantic City, NJ 19.0"
East Boston, MA 16.5"
Ocean City, MD 13.5"
NYC Central Park, NY 13.0"
Philadelphia, PA 12.4"
East Providence, RI 12.0"
Danbury, CT 11.1"
Augusta, ME 10.0"
Woodstock, VT 10.0"
Bridgeport, CT 8.0"
Boston, MA 6.5"
Wilmington, DE 3.4"

An unusual Nor'easter for a La Niña year
This winter, we are experiencing La Niña conditions in the Equatorial Eastern Pacific, meaning that cold waters have upwelled from the depths off the coast of South America, cooling a huge region of Pacific waters to below-average levels. In most winters, the presence of La Niña acts to deflect the jet stream in such a way the the predominant storm track takes winter storms into the Pacific Northwest, then down through the Upper Midwest and Ohio Valley. According to Dr. David A. Robinson, the New Jersey State Climatologist and Chairman of the Department of Geography at Rutgers University, this sort of flow pattern keeps New England safe from Nor'easters, as storms tend to move from the Ohio Valley northeastwards into Canada, keeping New England in a warm southwesterly flow of air. However, today's storm defied climatology, and gave the mid-Atlantic and New England one of their worst poundings on record for a La Niña Nor'easter. It was the first storm in at least ten La Niña winters, dating back to 1970, to bring 10" of more of snow to New Jersey, according to Dr. Robinson. In Philadelphia, which got 12.4" from this storm, the National Weather Service stated that only one La Niña winter in the past century has had a storm that dumped more than 10" of snow on city--a December 1909 Nor'easter. The reason for the unusual Nor'easter this year is that it happened to get started right when the atmosphere was transitioning from one major flow pattern to another. Since late November, we have been locked into a pattern featuring very weak low pressure over Iceland, and weak high pressure over the Azores--a strongly negative North Atlantic Oscillation (NAO) and Arctic Oscillation (AO). This pattern, which has allowed a lot of cold air to spill out of the Arctic and into the Eastern U.S. and Western Europe, is now breaking down and transitioning to a very different winter pattern. This new pattern will feature a more typical configuration for winter, with the Icelandic Low and Azores High close to their usual strengths. Today's Nor'easter managed to sneak in just as the atmosphere was transitioning from one major flow pattern to a new one, resulting in the rare La Niña snowstorm for New England. The new winter flow pattern looks to stay in place for at least the first two weeks of January, resulting in warmer than average winter weather for both the U.S. East Coast and Western Europe.

Jeff Masters

Winter Weather

November 2010 1st or 2nd warmest on record; ZombieSat saga ends

By: JeffMasters, 3:50 PM GMT on December 24, 2010

November 2010 was the globe's second warmest November on record, according to the National Oceanic and Atmospheric Administration (NOAA) National Climatic Data Center (NCDC). NASA's Goddard Institute for Space Studies rated November 2010 the warmest November on record. Both NOAA and NASA rated the year-to-date period, January - November, as the warmest such period on record. Global satellite-measured temperatures for the lowest 8 km of the atmosphere for November were the 5th or 3rd warmest on record, according to Remote Sensing Systems and the University of Alabama Huntsville (UAH), respectively. UAH rates the year-to-date period, January-November, as the 2nd warmest such period in the satellite data record, behind 1998. The record or near-record November global warmth is remarkable, given that we are in the midst of a moderate strength La Niña episode in the Eastern Pacific. The large amount of cold water that upwells to the surface during a La Niña typically causes a substantial cool-down in global temperatures, making a monthly temperature record difficult to set. November 2010 is the only "warmest month on record" as rated by NASA to occur during La Niña conditions. The November temperature record is all the more remarkable since we are near the minimum of the 11-year solar sunspot cycle. Global temperatures are cooler by about 0.1°C for the two years following a solar minimum, compared to global temperatures two years after solar maximum. Our current minimum in solar energy makes it much more difficult to set monthly global temperature records.

An average November for the U.S.
For the contiguous U.S., November was near-average in temperature, ranking as the 46th warmest November in the 116-year record, according to the National Climatic Data Center. The year-to-date period, January to November, was the 19th warmest such period on record. No states had a top-ten warmest or coldest November on record. November 2010 precipitation was also near average. Only Montana had a top-ten wettest November on record, and no states had top-ten driest November.

La Niña in the "moderate" category
The equatorial Eastern Pacific Ocean is currently experiencing moderate La Niña conditions. Sea surface temperatures (SSTs) over the tropical Eastern Pacific in the area 5°N - 5°S, 120°W - 170°W, also called the "Niña 3.4 region", were 1.4°C below average as of December 20, according to NOAA. The Australian Bureau of Meteorology put this number at 1.29°C below average (as of December 19.) Moderate La Niña conditions are defined as occurring when this number is 1.0°C - 1.5°C below average. Temperatures colder than 1.5°C below average qualify as strong La Niña conditions. NOAA is maintaining its La Niña advisory, and expects La Niña conditions to last through the coming winter into spring.

Both El Niño and La Niña events have major impacts on regional and global weather patterns. La Niña typically causes warm, dry winters over the southern portion of the U.S., with cooler and wetter than average conditions over the Pacific Northwest. The Ohio and Mississippi Valleys states typically have wetter winters than usual during La Niña events.

November 2010 Arctic sea ice extent 2nd lowest on record
Northern Hemisphere sea ice extent in November 2010 was the 2nd lowest in the 31-year satellite record behind 2006, according to the National Snow and Ice Data Center. As of December 24, ice extent was the lowest on record for this time of year. Ice volume in November was the lowest on record, according to University of Washington Polar Ice Center.

Figure 1. Sea ice extent in the Arctic as measured by satellites. Beginning in mid-December, ice extent was at record low levels for this time of year. Image credit: University of Bremen.

Major atmospheric pattern shift coming
The unseasonably cold weather over Europe and the Eastern U.S. is due to break between Christmas and New Year's, as the atmosphere undergoes a major shift in its circulation. The very unusual high pressure region over the Arctic is forecast to break down and be replaced by the typical low pressure region we expect to see in winter. After recording some of its coldest temperatures in 17 years this week, the UK may well see record highs on New Year's Eve as a result of the pattern shift. The pattern shift should bring the Eastern U.S. above-normal temperatures during the last few days of 2010, and a major New Year's Eve snowstorm to Iowa, Minnesota, and Wisconsin.

The ZombieSat saga ends?
Last week, I blogged about ZombieSat, the rogue Galaxy-15 communications satellite that failed during a solar storm. ZombieSat has been spewing noise in the C-band microwave region that has been interfering with broadcasts from satellites in its path, including the key SES-1 satellite that relays most of the weather data wunderground and the National Weather Service uses. Within the next week, ZombieSat will close in on its sister satellite, Galaxy-16, which hosts the Public Radio Satellite Service (PRSS) feeds, among others. A few weeks ago, PRSS warned its customers (who include commercial stations as well as the nation's public broadcasters) that there would be a possibility of disruption to its services on or about December 26. But on Friday December 17, Intelsat announced that ZombieSat had lost its "lock" on Earth, resulting in a loss of power that caused the satellite's main interfering transponders to shut down. So it appears the ZombieSat saga is over, and a whole bunch of engineers and operations directors can enjoy Christmas weekend without worrying about a zombie satellite hanging 23,000 miles over their heads.

Happy holidays, everyone!

Jeff Masters

Climate Summaries

Europe's cold and snowy winter forecast to gradually ease

By: JeffMasters, 5:25 PM GMT on December 23, 2010

It will be a white Christmas over most of the UK this year, an unusual occurrence in a nation where heavy snows typically occur just a few times per year. High temperatures in London over the past week have averaged about 6°C (11°F) below the average high of 7°C (44°F), and will remain below average through Christmas. Winter has hit Western Europe hard for over a month, with heavy snows significantly disrupting flights all across the continent. For November, the UK saw its heaviest and most widespread snows and coldest temperatures since 1993, and deepest snows since 1965. On Monday, December 20, the temperature plummeted to -18°C (0°F) at Castlederg in Northern Ireland in the UK. According to weather records researcher Maximiliano Herrera, who maintains a comprehensive set of world extreme temperature records on his web site, this beats the previous coldest temperature in Northern Ireland, -17.5°C at Magherally in January 1979. `

Figure 1. Temperatures for Dec. 20, 2010, were wildly different from average over much of the Northern Hemisphere. The British Isles shivered under temperatures 6 - 10°C (11 - 18°F) below average, and Northern Ireland set the record for its coldest temperature ever measured, -18°C (0°F) at Castlederg. At the same time, most of the Arctic had record-breaking temperatures up to 20°C (36°F) above average. Image credit: NOAA/ESRL.

Reasons for the cold weather in Europe
The exceptionally cold weather in Europe is due to a very unusual shift in the atmospheric circulation over the Northern Hemisphere in recent weeks that has allowed cold air to spill out of the Arctic into the mid-latitudes, and warm air to surge northwards into the Arctic. I discussed this Hot Arctic-Cold Continents pattern last week. The Arctic is usually dominated by low pressure and counter-clockwise circulating winds, and this "Arctic Vortex" has broken down and reversed its flow direction to clockwise, as high pressure is now in place over the Pole. Natural variability in the weather can cause this pattern, though significant loss of Arctic sea ice, such as occurred this fall, can also be a contributing factor. The extreme conditions in the Arctic this December has led to a rather remarkable event--sea ice decreased this week, during a period when we normally see some of the fastest rates of ice formation in the Arctic. Arctic sea ice extent is now at its lowest extent ever recorded for this time of year, due to the combined effects of unusual wind patterns and temperatures in excess of 10°C (18°F) above average over most of the Arctic.

Figure 2. The average surface pressure pattern in the Northern Hemisphere on December 20 between 1968 - 1996 (left panel) featured two familiar semi-permanent low pressure systems, the Icelandic Low and the Aleutian Low. Low pressure and counter-clockwise winds dominated the Arctic. But on December 20, 2010 (right panel), surface high pressure dominated the Arctic, and the normal flow of winds reversed from counter-clockwise to clockwise. The Icelandic Low and the Aleutian Low had shifted far to the south. This is an extremely unusual weather pattern for the Northern Hemisphere.

Major atmospheric pattern shift coming
The unseasonably cold weather is due to break in the UK next week, as the atmosphere undergoes a major shift in its circulation. The high pressure region over the Arctic is forecast to break down and be replaced by the usual low pressure region that typically dominates in winter. By New Year's, the Aleutian Low and Icelandic Low should re-establish themselves in their usual locations as the atmosphere reconfigures itself into a more typical pattern, and Europe should have near average to warmer than average temperatures for the first week of 2011.

Jeff Masters

Winter Weather

Atmospheric River deluges California and the Southwest

By: JeffMasters, 3:25 PM GMT on December 22, 2010

An “Atmospheric River” of extremely moist air continues to affect the Southwest U.S. today, and flooding rains of 1 – 2” with isolated amounts of 2 – 4” can be expected across Southern California, western and central Arizona, southeastern Nevada, and southwestern Utah. The heaviest rains will fall over the coastal mountains south of Los Angeles. The storm began on Friday night, and has brought some rather remarkable rains and snows to the Southwest. Crestline, California, in the mountains just east of Los Angeles, has received 20.05” of rain since Friday. The Sierra Mountains near Sequoia National Park received an astonishing 17 feet of snow at Pescoes since Friday night. Other heavy snow amounts from the storm include 6.4' at Heavenly near Lake Tahoe, 6.5' in Crested Butte, Colorado, and 9 – 13.5' in Mammoth in the Sierras. Some other rainfall amounts from NOAA's latest Storm Summary:

Iron Spring 11.14"
Black Rock 9.23"
Kingman 3.86"
Grand Canyon West 3.15"

Crestline 20.05"
Nature Point 18.60"
Tanback 16.94"
Mammoth Lakes 12.82"
Santa Barbara 12.39"
Los Angeles-USC 6.66"
San Diego 4.22"
San Francisco Airport 2.44"

Mount Charleston 12.66"
Las Vegas, 24 miles WNW 8.99"
Reno 2.59"

Gutz Peak 15.90"
Little Grassy 15.10"
Zion National Park 6.76"

Figure 1. The total amount of rainfall one could get if all the moisture in the air were condensed and fell out as rain is called the Total Precipitable Water (TPW). Here, TPW values from microwave satellite measurements are plotted, and show a plume of very moist air connecting the subtropics near Hawaii with Southern California. TPW vales in excess of 20 mm (about 0.8 inches, blue and warmer colors) are often associated with heavy rainfall events capable of causing flooding. Image credit: University of Wisconsin CIMSS.

“Atmospheric Rivers” was a term coined in the 1990s to describe plumes of moisture that ride up out of the subtropics into the mid-latitudes along the axis of a cold front. Traditional water vapor satellite imagery does not show these plumes very well, and it was only when microwave satellite imagery from polar orbiting satellites became available in the late 1990s that the full importance of these Atmospheric Rivers came to be revealed. Atmospheric Rivers account for a significant portion of California's cold season rainfall and snowfall, and an entire session was devoted to them at last week's American Geophysical Union (AGU) meeting in San Francisco, the world's largest Earth Science meeting.

Jeff Masters


Was the 2010 Haiti Earthquake triggered by deforestation and the 2008 hurricanes?

By: JeffMasters, 2:57 PM GMT on December 20, 2010

Major earthquakes occur when the stress on rocks between two tectonic plates reaches a critical breaking point, allowing the earth to move along the connecting fault. While the slow creep of the tectonic plates makes earthquakes inevitable along major faults, the timing and exact location of the quake epicenter can be influenced by outside forces pushing down on Earth's crust. For example, the sloshing of water into the Eastern Pacific during El Niño events has been linked to magnitude 4, 5, and 6 earthquakes on the seafloor below, due to the extra weight of water caused by local sea level rise. Sea level rise due to rapid melting of Earth's ice sheets could also potentially trigger earthquakes, though it is unknown at what melting rate such an effect might become significant.

Figure 1. Google Earth image of Haiti taken November 8, 2010, showing the capital of Port-Au-Prince and the mountainous region to its west where the epicenter of the 2010 earthquake was. Note the brown color of the mountains, where all the vegetation has been stripped off, leaving bare slopes subject to extreme erosion. Heavy rains in recent years have washed huge amounts of sediment into the Leogane Delta to the north.

Figure 2. Zoom-in view of the Leogane Delta region of Figure 1, showing the large expansion in the Delta's area between 2002 and 2010. High amounts of sediments have been eroded from Haiti's deforested mountains and deposited in the Delta. Recent expansion of the river channel due to runoff from Hurricane Tomas' rains is apparent in the 2010 image. Image credit: Google Earth, Digital Globe, GeoEye.

At last week's American Geophysical Union (AGU) meeting last week in San Francisco, Shimon Wdowinsky of the University of Miami proposed a different method whereby unusual strains on the crust might trigger an earthquake. In a talk titled, Triggering of the 2010 Haiti earthquake by hurricanes and possibly deforestation , Wdowinsky studied the stresses on Earth's crust over the epicenter of the mighty January 12, 2010 Haiti earthquake that killed over 200,000 people. This quake was centered in a mountainous area of southwest Haiti that has undergone severe deforestation—over 98% of the trees have been felled on the mountain in recent decades, allowing extreme erosion to occur during Haiti's frequent heavy rainfall events. Since 1975, the erosion rate in these mountains has been 6 mm/year, compared to the typical erosion rate of less than 1 mm/yr in forested tropical mountains. Satellite imagery (Figure 2) reveals that the eroded material has built up significantly in the Leogane Delta to the north of the earthquake's epicenter. In the 2008 hurricane season, four storms--Fay, Gustav, Hanna, and Ike--dumped heavy rains on the impoverished nation. The bare, rugged hillsides let flood waters rampage into large areas of the country, killing over 1,000, destroying 22,702 homes, and damaging another 84,625. About 800,000 people were affected--8% of Haiti's total population. The flood wiped out 70% of Haiti's crops, resulting in dozens of deaths of children due to malnutrition in the months following the storms. Damage was estimated at over $1 billion, the costliest natural disaster in Haitian history. The damage amounted to over 5% of the country's $17 billion GDP, a staggering blow for a nation so poor. Tragically, the hurricanes of 2008 may have set up Haiti for an ever larger disaster. Wdowinsky computed that the amount of mass eroded away from the mountains over the epicenter of the 2010 earthquake was sufficient to cause crustal strains capable of causing a vertically-oriented slippage along a previously unknown fault. This type of motion is quite unusual in this region, as most quakes in Haiti tend to be of the strike-slip variety, where the tectonic plates slide horizontally past each other. The fact that the 2010 Haiti quake occurred along a vertically moving fault lends support to the idea that the slippage was triggered due to mass stripped off the mountains by erosion over the epicenter, combined with the extra weight of the extra sediment deposited in the Leogane Delta clamping down on the northern portion of the fault. Wdowinsky gave two other examples in Taiwan where earthquakes followed several months after the passage of tropical cyclones that dumped heavy rains over mountainous regions. His theory of tropical cyclone-triggered quakes deserves consideration, and provides another excellent reason to curb excessive deforestation!

Figure 3. Two of 2008's four tropical cyclones that ravaged Haiti: Tropical Storm Hanna (right) and Hurricane Gustav (left). Image taken at 10:40 am EDT September 1, 2008. Image credit: NASA/GSFC.

Christmas in Haiti will brighten the lives of hundreds of kids in Haiti this week, thanks to their successful Christmas in Haiti fundraiser. Portlight raised $1800 to buy toys, candies, and other assorted goodies. The shipment left Charleston last week, and will arrive in time for Christmas. Thanks to everyone who helped support this worthy effort!

Jeff Masters

Hurricane Earthquake

Key weather relay satellite survives encounter with ZombieSat

By: JeffMasters, 3:55 PM GMT on December 16, 2010

On April 3, 2010, the sun's surface erupted in a magnetic disturbance known as a Coronal Mass Ejection (CME). A chuck of the sun's atmosphere ripped away and hurtled through space towards the Earth, arriving two days later. As Coronal Mass Ejections go, this was a garden-variety one, the kind we see dozens of times per year. However, when the high energy electrons and protons associated with the CME reached Earth's magnetosphere on April 5, an unusually strong solar storm developed, the strongest in three years. While we have no direct proof that this space weather storm was responsible, an Intelsat telecommunications satellite called Galaxy 15, used to relay television programs, suddenly lost contact with ground controllers and began drifting through space. According to scientists at NOAA's Space Weather Prediction Center whom I met with on a site visit this summer, solar storms have probably knocked out at least a dozen satellites in the fifty years humans have been launching them. Usually, these dead satellites pose no threat to other satellites. But the Galaxy 15 satellite has joined the ranks of the undead and become "ZombieSat". Although no television signals are being bounced off of the satellite, its transponders remain active and are spewing out a high volume of noise in the microwave C-band. As ZombieSat drifted uncontrolled through space this year, interference from the satellite threatened to shut down transmissions from a number of communications satellites in its path. In May, SES World Skies was forced to maneuver their AMC-11 satellite out of the way of ZombieSat to avoid its interference. And yesterday, on December 15, ZombieSat made a close pass by the SES-1 communications satellite. This satellite downlinks the NOAAPORT weather data feed, which supplies nearly all of the weather data used by wunderground, the National Weather Service, and many other users. For a ten hour period yesterday, interference from ZombieSat significantly interfered with the NOAAPORT data feed, causing many data transmission errors.

Figure 1. This is a close-up view of the active region observed by Proba-2's SWAP (Sun Watcher using APS detectors and imaging processing) instrument on 3 April 2010. Magnetic loops are visibly glowing--filled with cooling plasma (though cooling is a relative phrase, its temperature still exceeds a million degrees)--as the Sun's magnetic field knits itself together again in the flare's immediate aftermath. The area around the magnetic loops is darkened due to the Sun's surface reacting to the force of the flare. Image credit: European Space Agency.

Fortunately, little or no weather data was permanently lost during ZombieSat's encounter with SES-1. Much of the credit for this goes to NOAA technicians who devised an alternate satellite data transimission scheme to reduce the amount of interference from ZombieSat. Over the past week, the NOAAPORT data has been routed as usual from the National Weather Service in Washington D.C. to the Primary Master Ground Station located in Hauppauge, NY, via terrestrial communication lines. The Hauppauge ground station has been broadcasting the NOAAPORT feed to a "borrowed" satellite, which bounces the signal to the SES Americom Master Ground Station in Hawaii, which is outside the interference "footprint" of ZombieSat. NOAAPORT then is then uplinked to the SES-1 satellite, and then beamed down to Earth to Weather Underground, the NWS, and the other NOAAPORT subscribers. This way, NOAAPORT has been avoiding seeing interference from ZombieSat during the uplink to the SES-1 satellite. However, the signal is still subject to interference during the downlink process, and ZombieSat may still be able to cause trouble for NOAAPORT over the next few days. By Sunday, ZombieSat will be far enough from SES-1 that NOAA can return NOAAPORT back to its original configuration. Kudos go to NOAA for safely managing to keep NOAAPORT functioning during ZombieSat's passage--had they not acted to re-route the NOAAPORT signal, the U.S. could have seen a significant and potentially dangerous loss of weather data. (However, this did not go off without a hitch--technicians experimenting with adjusting power levels for the NOAAPORT feed during testing of the re-routing scheme accidentally knocked NOAAPORT out for several hours a week ago Sunday.)

Figure 2. Data flow diagram of how weather data gets from the National Weather Service (NWS) and NOAA's Satellite and Information Service (NESDIS) through the NOAA Network Control Facility (NCF) onto the NOAAPORT feed that is relayed off of the SES-1 satellite to NOAAPORT receive ground stations. Image credit: NOAA.

How solar storms damage spacecraft
The region of space where most Earth-orbiting satellites lie, 100 - 23,000 miles above the surface, experiences "space weather"--constant bombardment from high energy particles emitted by the sun. Periodically, the sun erupts in a massive magnetic disturbances known as Coronal Mass Ejections (CMEs), when a portion of the sun's atmosphere rips away and hurtles into space. The sun also sends out high-energy particles during solar flares, and when holes open in the sun's outer atmosphere (a coronal "hole"). When these solar particles reach Earth's upper atmosphere, they trigger geomagnetic storms that create the beautiful aurora displays often visible at high latitudes. However, these geomagnetic storms can damage a wide range of electronic systems, including power grids, communications systems, and spacecraft. When high-energy protons and ions hit spacecraft, the ionization tracks left in micro-miniaturized electronics can damage computer memory chips or disrupt circuits. Very energetic electrons can also penetrate deep into satellites bury themselves in insulating materials, such as coaxial cables or electronic boards. A powerful internal electronic discharge like a miniature lightning bolt can occur if the charge grows great enough. Numerous satellite failures have been attributed to this phenomena. Lower energy electrons that cannot penetrate the spacecraft's shielding can also cause problems--if enough electrons accumulate on the surface of the satellite, this "surface charging" can cause a powerful, disruptive discharge. Ionization tracks and discharges due to surface charging can result in the satellite experiencing "phantom commands" that instruct it to perform operations that can cut it off from contact with ground controllers. Such an occurrence is suspected in the sudden loss of communication with the Galaxy 15 spacecraft on April 5.

Damage to spacecraft due to space weather events does not necessarily happen during the peak of the 11-year solar cycle. The most recent sunspot cycle peaked in April 2000, and sunspot numbers steadily decreased through October 2003. In that month, three of the largest sunspot groups in ten years formed on the sun and began launching a series of CMEs and solar flares towards Earth, forcing NOAA's Space Weather Prediction Center to issue over 250 solar storm watches, warnings, and alerts over a 3-week period. NASA reported that 24% of their spacecraft either turned off instruments or took other protective acts during the solar storms. Japan's $640 million ADEOS-2 satellite, designed to collect weather and climate change data, failed during the height of the solar storms, and never recovered. Several other satellites permanently lost sensors, including the X-ray sensor on GOES-8 and the AMSU-A1 instrument on NOAA-17. The CHIPS satellite began tumbling through space when its main computer failed (the satellite was recovered after 27 hours), and Japan's DRTS geostationary communications satellite want into safe mode due to a proton barrage from a solar flare. The satellite was recovered ten days later.

Figure 3. The largest solar flare ever recorded was observed on April 2, 2001. It was rated X-22 on a scale that only goes from one to twenty. The flare was more powerful than the flare that accompanied the worst geomagnetic storm in history, the 1859 Carrington event. Fortunately, the 2001 flare was not aimed at the Earth. Image credit: NASA.

Space weather catastrophes
While damage to satellites is a serious concern from geomagnetic storms, my main concern is the possibility of a 1-in-100 year event taking out 30% of the U.S. power grid for a period of years, resulting in a multi-trillion dollar disaster. The possibilities are explored in my 2009 post, A future Space Weather catastrophe: a disturbing possibility.

Top ten weather events of 2010
I'll be on our Internet radio show, The Daily Downpour today at 4pm EST, 1pm PST, to talk about the top ten weather events of 2010. I'll also be discussion the same subject on NPR's Living on Earth radio show on Friday.

Jeff Masters

Florida shivers; Hot Arctic-Cold Continents pattern is back

By: JeffMasters, 5:36 PM GMT on December 14, 2010

Cold air sweeping southwards behind the fierce snowstorm that roared through the Upper Midwest over the weekend is bringing record low temperatures over much of the Southeast this morning. However, preliminary indications are that Central Florida's orange groves fared better than expected, and there were no reports of widespread damage to the orange crop. Record lows this morning included 32°F at West Palm Beach, 50°F in Key West, and 20°F in Jacksonville. Cold air flowing over the relatively warm waters of Lake Erie and Lake Ontario are creating heavy lake-effect snows, with 5 – 9 inches of new snow expected near Cleveland, OH today, and 2 – 5 inches near Syracuse, NY.

Hot Arctic-Cold Continents
I'm in San Francisco this week for the world's largest gathering of Earth scientists, the annual American Geophysical Union (AGU) conference. Over 15,000 scientists have descended upon the city, and there are a ridiculous number of fascinating talks on every conceivable aspect of Earth science, including, of course, climate change. One talk I attended yesterday was called, "Hot Arctic-Cold Continents: Hemispheric Impacts of Arctic Change.” The talk was given by Dr. Jim Overland of NOAA's Pacific Marine Environmental Laboratory, one of the world's experts on Arctic weather and climate (I spent many long months flying in the Arctic with him during the three Arctic field programs I participated in during the late 1980s.) Dr. Overland discussed the remarkable winter of 2009 – 2010, which brought record snowstorms to Europe and the U.S. East Coast, along with the coldest temperatures in 25 years, but also brought the warmest winter on record to Canada and much of the Arctic. He demonstrated that the Arctic is normally dominated by low pressure in winter, and a “Polar Vortex” of counter-clockwise circulating winds develops surrounding the North Pole. However, during the winter of 2009-2010, high pressure replaced low pressure over the Arctic, and the Polar Vortex weakened and even reversed at times, with a clockwise flow of air replacing the usual counter-clockwise flow of air around the pole. This unusual flow pattern allowed cold air to spill southwards and be replaced by warm air moving poleward. This pattern is kind of like leaving the refrigerator door ajar--the refrigerator warms up, but all of the cold air spills out into the house.

Figure 1. Conceptual diagram of how Arctic sea ice loss affects winter weather, from NOAA's Future of Arctic Sea Ice and Global Impacts web page.

The North Atlantic Oscillation (NAO)
This is all part of a natural climate pattern known as the North Atlantic Oscillation (NAO), which took on its most extreme configuration in 145 years of record keeping during the winter of 2009 – 2010. The NAO is a climate pattern in the North Atlantic Ocean of fluctuations in the difference of sea-level pressure between the Icelandic Low and the Azores High. It is one of oldest known climate oscillations--seafaring Scandinavians described the pattern several centuries ago. Through east-west oscillation motions of the Icelandic Low and the Azores High, the NAO controls the strength and direction of westerly winds and storm tracks across the North Atlantic. A large difference in the pressure between Iceland and the Azores (positive NAO) leads to increased westerly winds and mild and wet winters in Europe. Positive NAO conditions also cause the Icelandic Low to draw a stronger south-westerly flow of air over eastern North America, preventing Arctic air from plunging southward. In contrast, if the difference in sea-level pressure between Iceland and the Azores is small (negative NAO), westerly winds are suppressed, allowing Arctic air to spill southwards into eastern North America more readily. Negative NAO winters tend to bring cold winters to Europe and the U.S. East Coast, but leads to very warm conditions in the Arctic, since all the cold air spilling out of the Arctic gets replaced by warm air flowing poleward.

The winter of 2009 - 2010 had the most extreme negative NAO since record keeping began in 1865. This "Hot Arctic-Cold Continents pattern", resulting in a reversal of Polar Vortex and high pressure replacing low pressure over the Arctic, had occurred previously in only four winters during the past 160 years—1969, 1963, 1936, and 1881. Dr. Overland called the winter of 2009 – 2010 at least as surprising at the record 2007 loss of Arctic sea ice. He suspected that Arctic sea ice loss was a likely culprit for the event, since Francis et al. (2009) found that during 1979 - 2006, years that had unusually low summertime Arctic sea ice had a 10 - 20% reduction in the temperature difference between the Equator and North Pole. This resulted in a weaker jet stream with slower winds that lasted a full six months, through fall and winter. The weaker jet caused a weaker Aleutian Low and Icelandic Low during the winter, resulting in a more negative North Atlantic Oscillation, allowing cold air to spill out of the Arctic and into Europe and the Eastern U.S. Dr. Overland also stressed that natural chaos in the weather/climate system also played a role, as well as the El Niño/La Niña cycle and natural oscillations in stratospheric winds. Not every year that we see extremely high levels of Arctic sea ice loss will have a strongly negative NAO winter. For example, the record Arctic sea ice loss year of 2007 saw only a modest perturbation to the Arctic Vortex and the NAO during the winter of 2007 – 2008.

However, the strongly negative NAO is back again this winter. High pressure has replaced low pressure over the North Pole, and according to NOAA, the NAO index during November 2010 was the second lowest since 1950. This strongly negative NAO has continued into December, and we are on course to have a top-five most extreme December NAO. Cold air is once again spilling southwards into the Eastern U.S. And Europe, bringing record cold and fierce snowstorms. At the same time, warm air is flowing into the Arctic to replace the cold air spilling south--temperatures averaged more than 10°C (18°F) above average over much of Greenland so far this month. The latest 2-week forecast from the GFS model predicts that the Hot Arctic-Cold Continents pattern will continue for the next two weeks. However, the coldest air has sloshed over into Europe and Asia, and North America will see relatively seasonable temperatures the next two weeks.

For more information
The NOAA web page, Future of Arctic Sea Ice and Global Impacts has a nice summary of the “Hot Arctic-Cold Continents” winter pattern.

NOAA's Arctic Report Card is also a good source of information.

Francis, J. A., W. Chan, D. J. Leathers, J. R. Miller, and D. E. Veron, 2009: Winter northern hemisphere weather patterns remember summer Arctic sea-ice extent. Geophys. Res. Lett., 36, L07503, doi:10.1029/2009GL037274.

Honda, M., J. Inoue, and S. Yamane, 2009: Influence of low Arctic sea-ice minima on anomalously cold Eurasian winters. Geophys. Res. Lett., 36, L08707, doi:10.1029/2008GL037079.

Overland, J. E., and M. Wang, 2010: Large-scale atmospheric circulation changes associated with the recent loss of Arctic sea ice. Tellus, 62A, 1.9.

Petoukhov, V., and V. Semenov, 2010: A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents. J. Geophys. Res.-Atmos., ISSN 0148-0227.

Seager, R., Y. Kushnir, J. Nakamura, M. Ting, and N. Naik (2010), Northern Hemisphere winter snow anomalies: ENSO, NAO and the winter of 2009/10, Geophys. Res. Lett., 37, L14703, doi:10.1029/2010GL043830.

Jeff Masters

Climate Change Sea Ice Winter Weather

Heavy snow collapses Minneapolis Metrodome roof

By: JeffMasters, 6:22 PM GMT on December 12, 2010

A raging December blizzard buried Minneapolis, Minnesota under 17 inches of snow over the weekend, triggering the collapse early this morning of the air-inflated roof of the Minneapolis Metrodome, home of the Minnesota Vikings football team. The storm roared out of Canada on Friday morning, bringing heavy snow, sustained winds of 25 – 35 mph, and blizzard conditions through Montana, North Dakota, South Dakota, Minnesota, Wisconsin, and Michigan. The heaviest snows occurred near Osceola, Wisconsin, where 23 inches fell. The storm also dumped 21" at Noisy Basin, Montana, 14" in Williston, ND, and 14" in Negaunee, MI. Officially, 17.1” of snow fell at the Minneapolis airport; 16.3” of it on Saturday. Saturday's snow amounted to 1.75” of melted precipitation, for a snow-to-water equivalent ratio of 9:1. For those of you who've ever shoveled snow know, that's a very wet, heavy snow, and its no wonder the roof of the Metrodome had trouble with such a huge weight of snow.

Figure 1. Amount of precipitation for the 24 hours ending at 1am EST Sunday, in melted snow equivalent. Up to two inches of precipitation fell (brown colors) near the Minnesota-Wisconsin border. Image credit: NOAA /NOHRSC.

In the wake of the storm, bitterly cold air from Canada will sweep southwards into the U.S., and high temperatures near 0°F are expected for Minneapolis on Monday. Lows near -30°F are expected in northern Minnesota near International Falls on Monday night. The cold will penetrate into Florida's orange groves Monday night, with lows in the mid-20s expected in Orlando.

Jeff Masters

Winter Weather

CSU and TSR predict an extremely active 2011 Atlantic hurricane season

By: JeffMasters, 12:54 PM GMT on December 09, 2010

A continuation of the pattern of much above-average Atlantic hurricane activity we've seen since 1995 is on tap for 2011, according to the latest seasonal forecast issued Wednesday by Dr. Phil Klotzbach and Dr. Bill Gray of Colorado State University (CSU). They are calling for 17 named storms, 9 hurricanes, and 5 intense hurricanes. An average season has 10 - 11 named storms, 6 hurricanes, and 2 intense hurricanes. The new forecast is a very aggressive one, since only six seasons since 1851 have had as many as 17 named storms; 19 seasons have had 9 or more hurricanes. The 2011 forecast calls for a much above-average chance of a major hurricane hitting the U.S., both along the East Coast (49% chance, 31% chance is average) and the Gulf Coast (48% chance, 30% chance is average). The Caribbean is forecast to have a 62% chance of seeing at least one major hurricane (42% is average.) Five years with similar pre-season November atmospheric and oceanic conditions were selected as "analogue" years that the 2011 hurricane season may resemble: 2008, 1999, 1989, 1961, and 1956. The average activity for these years was 12 named storms, 7 hurricanes, and 4 major hurricanes.

The forecasters cited several reasons for their forecast of a much above-average season:

1) Unusually warm sea surface temperatures continue in the tropical Atlantic this fall, an indication that the active hurricane period we have been in since 1995 will continue (in technical terms, the positive phase of the Atlantic Multidecadal Oscillation, AMO, will continue.) SSTs in Atlantic Main Development Region (MDR) for hurricanes, from the Caribbean eastwards to the coast of Africa, were at a record high in October (November data are not yet available.)

2) Hurricane activity in the Atlantic is lowest during El Niño years and highest during La Niña or neutral years. This occurs because El Niño events tend to increase westerly upper-level winds over the tropical Atlantic, bringing high wind shear harmful for hurricanes. The CSU team notes that we are currently experiencing moderate to strong La Niña conditions, with an unusual amount of cool water present in the top 300 meters of the Equatorial Pacific Ocean off the coast of South America. Since 1979, only eight years have had similar amounts of cool water in November. The hurricane seasons that followed each of those eight years were unable to transition to El Niño conditions. Thus, the CSU team expects that we will have neutral or La Niña conditions in place for the Atlantic hurricane season of 2011, which should act to keep wind shear values average to below average, enhancing hurricane activity. Of the 16 El Niño/La Niña computer models that made November predictions for the July-August-September 2011 portion of hurricane season (Figure 1), only 4 (25%) predicted that El Niño would arrive.

How accurate are the December forecasts?
The CSU real-time December forecasts did not shown any skill over the period 1992 - 2007, so the forecast scheme was overhauled and a new scheme implemented for the forecasts made for the 2008 - 2010 hurricane seasons. This new scheme showed some decent skill in those three years, with skill levels 18%, 10%, and 30% above chance for predicting the number of named storms, hurricanes, and intense hurricanes, respectively. Still, three years is too short of a time period to evaluate the skill of these December forecasts, and we should view the latest forecast as an experimental research product. Last year's December forecast for the 2010 hurricane season predicted 13.5 named storms, 7 hurricanes, and 4 intense hurricanes. The actual numbers were 19 named storms, 12 hurricanes, and 5 intense hurricanes.

Figure 1. Forecasts of El Niño conditions by 20 computer models, made in November 2010. The longest range forecasts for July-August-September (JAS) at the right side of the image show that 4 models predict weak El Niño conditions, 7 predict neutral conditions, and 5 predict a weak to moderate La Niña. El Niño conditions are defined as occurring when sea surface temperatures in the Equatorial Pacific off the coast of South America (the "Niño 3.4 region) rise to 0.5°C above average (top red line). La Niña conditions occur when SSTs in this region fall to 0.5°C below average. Image credit: Columbia University.

2011 Atlantic hurricane season forecast from Tropical Storm Risk, Inc.
The British private forecasting firm Tropical Storm Risk, Inc. (TSR), issued their 2011 Atlantic hurricane season forecast on Monday. They are also calling for a very active year: 15.6 named storms, 8.4 hurricanes, and 4 intense hurricanes. TSR predicts a 66% chance of an above-average hurricane season, 22% chance of a near-normal season, and only a 12% chance of a below normal season. TSR bases their December forecast on predictions that sea surface temperatures next fall in the tropical Atlantic will be above about 0.3°C above average, and trade wind speeds will be about 0.7 m/s slower than average. The trade wind speed prediction is based on a forecast for a weak La Niña in August-September 2011.

I like how TSR puts their skill level right next to the forecast numbers: 2% skill above chance at forecasting the number of named storms, 1% skill for hurricanes, and 7% skill for intense hurricanes. That's not much skill, and really, we have to wait until the June 1 forecasts by CSU, NOAA, and TSR to get a forecast with reasonable skill.

Comparing 2005 and 2010 steering currents
The U.S. got extremely fortunate during the 2010 hurricane season that the steering currents carried most of the storms out to sea, or forced them to the south. A very graphic way of looking at this is to compare the amount of rain that fell due to tropical cyclones in the Atlantic in 2005 versus 2010 (Figure 2.) The U.S. received a direct hit only from Tropical Storm Bonnie, which hit South Florida as a minimal 40 mph tropical storm and caused no significant damage. TSR is predicting that this luck will not hold in 2010; they project that five named storms will hit the U.S., with two of these being hurricanes.

Figure 2. Rainfall amounts due to all Atlantic tropical cyclones in 2005 and 2010, as measured by NASA's TRMM satellite. Steering currents in 2010 tended to recurve many storms out to sea between the Caribbean and Bermuda, due to a large number of unusually strong troughs of low pressure moving off the U.S. East Coast.

Weekend winter storm for Eastern U.S.
The latest 06Z (1am EST) set of computer model forecasts for this weekend's winter storm over the Midwest and Eastern U.S. point towards a more northerly path for the storm, bringing the axis of heaviest snow through Wisconsin and Michigan. There is still a great deal of uncertainty in the predicted timing and strength of the storm, but a renewed blast of cold air Monday and Tuesday over the Southeast U.S. is still highly likely in the wake of the storm.

Jeff Masters


Major Pacific Northwest winter storm poised to slam Eastern U.S. this weekend

By: JeffMasters, 2:11 PM GMT on December 08, 2010

A major winter storm powered ashore today in the Pacific Northwest, bringing heavy rain and snow to the Olympic Mountains. This storm dumped four inches of rain over the Olympics, bringing the Skokomish River to flood stage. Record warm temperatures ahead of the storm have surged northwards across the Pacific Northwest, with Seattle, Washington hitting a record high of 55°F yesterday. Snowfall amounts approaching 2 feet are expected in the Olympic Mountains from the storm, with 1 - 3 feet likely in the Cascade Mountains. This is typical sort of storm one expects to see during a La Niña winter.

Figure 1. Radar-estimated precipitation from the Seattle radar for the period Dec 7 - Dec 8. Precipitation amounts in excess of 4 inches have occurred over the Olympic Mountains. Mountains surrounding Seattle block the radar beam, leading to the streaky nature of the image.

As the storm tracks eastwards over the Central U.S. later this week, it will intensify and pull in a large amount of cold, Canadian air. The latest set of computer model runs have come into much better agreement on the track of the storm, and a band of heavy snow of 6 - 10 inches is likely to set up over Central Illinois on Saturday afternoon. The storm will move rapidly eastwards, with the heaviest snow likely to impact northern Indiana, northern Ohio, and southern Ontario on Sunday. The biggest cold blast of the season thus far will roar in behind the storm, causing widespread blowing and drifting of the snow, plus new heavy Lake-effect snows in the lee of the Great Lakes. Low temperatures approaching -20°F are likely in northern Minnesota Saturday and Sunday night after the storm passes. By Tuesday morning, much of the eastern half of the nation will shiver through one the coldest mornings on record for the first half of December, with below freezing temperatures expected to penetrate all the way into South Florida. Record lows were set across much of Southeast U.S. this morning, with 39°F at Fort Lauderdale, 16°F in Columbia SC, and 9°F in Lychburg, VA. Temperatures much colder than this are likely on Tuesday morning across the region.

Figure 2. Forecast surface temperature for 7am EST on Tuesday, December 14, as predicted by this morning's 1am EST run of the GFS model. The heavy red line running along the coast of Florida is the 0°C freezing line, and temperatures below freezing are expected across nearly all of the Southeast U.S.

I'll have a new post on Thursday, when I'll discuss the CSU and TSR forecasts for the 2011 hurricane season. The TSR forecast was released Monday, and the CSU forecast is due out later today.

Jeff Masters

Winter Weather

Heaviest rains in Colombia's history trigger deadly landslide; 145 dead or missing

By: JeffMasters, 9:07 PM GMT on December 06, 2010

Colombia's heaviest rains in history triggered a landslide in the poor hillside community of Bello on Sunday, killing at least 20 people and leaving 125 missing. This year's unprecedented rainy season had already killed 176 people prior to Sunday, making it one of the deadliest flooding years in Colombia's history, according to the director of Colombia's national disaster management office, Luz Armanda Pulido. In 2009, 110 people died in flooding disasters, and 48 were killed in 2008, according to Colombian Red Cross director of national relief operations Carlos Ivan Marquez. This year's rains are the heaviest in the 42 years since Colombia's weather service was created and began taking data, agency director Ricardo Lozano said. The resulting flooding has destroyed or damaged the homes of 1.6 million people. Colombia's president Juan Manuel Santos said the number of homeless from the flooding could reach 2 million, and said "the tragedy the country is going through has no precedents in our history." Neighboring Venezuela has also been hard-hit by this year's severe rainy season--at least 30 people are dead from floods and mudslides, and tens of thousands homeless. More rain is in the forecast--the latest forecast from the GFS model (Figure 2)--calls for an additional 4 - 6 inches (100 - 150 mm) across much of western and northern Colombia in the coming week.

Figure 1. Satellite-observed rainfall over Colombia during the past two weeks shows a region of 100 - 200 mm (4 - 8 inches) has fallen near Medellin, close to where Sunday's landslide in Bello occurred. Image credit: Navy Research Lab, Monterey.

Colombia's rainy season usually peaks in October, then gradually wanes in November and December. The heavy rains are due to the presence of the Intertropical Convergence Zone, the area encircling the earth near the Equator where winds originating in the northern and southern hemispheres come together. When these great wind belts come together (or "converge", thus the name "Convergence Zone"), the converging air is forced upwards, since it has nowhere else to go. The rising air fuels strong thunderstorm updrafts, creating a band of very heavy storms capable of causing heavy flooding rains. This year is a La Niña year, which means there is a large region of colder than average water off the Pacific coast of Colombia. Colder than average water off the Pacific coast enhances rainfall over Colombia, and this year's La Niña, which is at the borderline between the "moderate" and "strong" categories, is largely to blame for Colombia's deadly rainy season.

Figure 2. Rainfall forecast from today's run of the GFS model predicts that region to the north and west of Bogota, Colombia may see another 100 - 150 mm (4 - 6 inches) during the coming week (red colors.) Image credit: NOAA/CPC.

See also my November 22 post, Colombia rainy season floods kill 136.

I'll have a new post on Wednesday.

Jeff Masters


Amazon rainforest recovering from its second 100-year drought in 5 years

By: JeffMasters, 2:32 PM GMT on December 03, 2010

Life-giving rains have returned over the past two months to Earth's greatest rainforest--the mighty Amazon--after it experienced its second 100-year drought in five years this year. The record drought began in April, during the usual start to the region's dry season, when rainfall less than 75% of average fell over much of the southern Amazon (Figure 2.) The drought continued through September, and by October, when the rainy season finally arrived, the largest northern tributary of the Amazon River--the Rio Negro--had dropped to thirteen feet (four meters) below its usual dry season level. This was its lowest level since record keeping began in 1902. The low water mark is all the more remarkable since the Rio Negro caused devastating flooding in 2009, when it hit an all-time record high, 53 ft (16 m) higher than the 2010 record low. The 2010 drought is similar in intensity and scope to the region's previous 100-year drought, which hit the Amazon in 2005, according to Brazil's National Institute of Space Research. Severe fires burned throughout the Amazon in both 2005 and 2010, leading to declarations of states of emergencies.

Figure 1. Hundreds of fires (red squares) generate thick smoke over a 1000 mile-wide region of the southern Amazon rain forest in this image taken by NASA's Aqua satellite on August 16, 2010. The Bolivian government declared a state of emergency in mid-August due to the out-of-control fires burning over much of the country. Image credit: NASA.

Causes of the great 2010 Amazon drought
During the 20th Century, drought was a frequent visitor to the Amazon, with significant droughts occurring an average of once every twelve years. These droughts typically occurred during El Niño years, when the unusually warm waters present along the Pacific coast of South America altered rainfall patterns. But 2010 was a La Niña year. The 100-year drought of 2005 occurred in an El Niño-neutral year. Subsequent analysis of the 2005 drought revealed that it was unlike previous El Niño-driven droughts, and instead was caused by record warm sea surface temperatures in the Atlantic (Phillips et al., 2009.) These warm ocean waters affected the southern 2/3 of the Amazon though reduced precipitation and higher than average temperatures. Very similar record Atlantic sea surface temperatures were observed in 2010, and likely were the dominant cause for the 2010 drought.

Figure 2. The great Amazon drought of 2010 began in April, when portions of the southern Amazon recorded precipitation amounts less than 75% of normal (brown colors). The drought spread northward and peaked during July and August, but drew to a close by November when the rainy season began. Image credit: NOAA Climate Prediction Center.

The importance of the Amazon to Earth's climate
We often hear about how important Arctic sea ice is for keeping Earth's climate cool, but the Amazon may be even more important. Photosynthesis in the world's largest rainforest takes about 2 billion tons of carbon dioxide out of the air each year. However, in 2005, the drought reversed this process. The Amazon emitted 3 billion tons of CO2 to the atmosphere, causing a net 5 billion ton increase in CO2 to the atmosphere--roughly equivalent to 16 - 22% of the total CO2 emissions to the atmosphere from burning fossil fuels that year. According to Phillips et al., 2009, "The exceptional growth in atmospheric CO2 concentrations in 2005, the third greatest in the global record, may have been partially caused by the Amazon drought effects documented here." The Amazon stores CO2 in its soils and biomass equivalent to about fifteen years of human-caused emissions, so a massive die-back of the forest could greatly accelerate global warming. In late 2009, before the 2010 drought, the World Wildlife Federation released a report, Major Tipping Points in the Earth's Climate System and Consequences for the Insurance Sector, which suggested that odds of extreme 2005-like droughts in the Amazon had increased from once every 40 - 100 years, to once every 20 years. The study projected that the extreme droughts would occur once every two years by 2025 - 2050. This year's drought gives me concern that this prediction may be correct. The occurrence of two extreme droughts in the past five years, when no El Niño conditions were present and record warm Atlantic sea surface temperatures occurred, are suggestive of a link between global warming and extreme Amazon drought. If the climate continues to warm as expected, the future health of Earth's greatest rainforest may be greatly threatened, and the Amazon may begin acting to increase the rate of global warming. According to Rosie Fisher, a scientist at the National Center for Atmospheric Research in Boulder, Colorado who specializes in interactions between climate and forests, "I'm genuinely quite alarmed by this. In some ways it kind of reminds me of when they figured out than the Greenland ice sheet was melting much faster than the climate models predicted it would."

Deforestation in Brazilian Amazon falls to lowest rate on record
There is some good news from the Amazon--deforestation rates in the Brazilian Amazon have fallen 14% in the past year, and are at their lowest rate on record, according to, an environmental science and conservation news site that focuses on tropical forests. In 2009, Brazil passed a law committing to a 36 - 39% reduction in emissions of greenhouse gases. Reducing deforestation by 80% by 2020 was the primary method envisioned to achieve the reduction. Brazil is now four years ahead of that schedule, and no longer is the world's biggest deforester--Indonesia now cuts down more acreage of forest each year than Brazil does.

For more information
Nick Sundt at the WWF Climate Blog has a remarkably detailed post on this year's Amazon drought, and Dr. Joe Romm at has another excellent post.

Phillips, et al., 2009, Drought Sensitivity of the Amazon Rainforest, Science 6 March 2009: Vol. 323 no. 5919 pp. 1344-1347 DOI: 10.1126/science.1164033.

I'll have new post Monday or Tuesday.

Jeff Masters

Climate Change Drought

The Wall of Wind: destroying buildings in the cause of science

By: JeffMasters, 1:00 PM GMT on December 02, 2010

During my week at the National Hurricane Center this October that I spent as part of their Visiting Scientist Program, I had the opportunity to visit one of the most remarkable engineering efforts used in hurricane research--the International Hurricane Research Center's "Wall of Wind" (WoW) on the campus of Florida International University. As I pulled into the parking lot next to the big metal building that houses the Wall of Wind research lab, I was met by Erik Salna, the Associate Director of the International Hurricane Research Center. He walked me over to their 2-story high "Wall of Wind", which consists of a bank of six 500 horsepower "hot-rod" auto engines with propellers attached, arranged in a box pattern. When the six engines are all fired up, they can generate Category 1 hurricane wind speeds of 80 - 85 mph (not to mention an unholy racket!) Researchers at the Wall of Wind study how full-scale buildings fare under the onslaught of these winds, and in the presence of flying debris and wind-driven rain. Fifteen peer-reviewed journal articles have resulted from WoW research, and changes to the Florida Building Code for 2010 have been recommended by the Technical Advisory Committee at the 2010 Florida Building Code meeting, based on WoW research. It was pretty cool to see how the WoW group tested different shingles, roof slopes, and roof edge and corner designs by wiring the roofs being tested with an elaborate network of pressure transducers. WoW research has shown the importance of protecting your windows with shutters--an open window in a house with a ceiling hatch increases the wind load on the windward side of a gable roof by 45%, greatly increasing the chances of complete roof failure.

Figure 1. Now if I just reach out and flip the switch to my left, my hair will get massively blow-dried! The current 6-fan version of the Wall of Wind (which became operational in 2007) can generate Category 1 hurricane winds of 80 - 85 mph. The reinsurance company Renaissance Re Holdings Ltd provided the funding for the 6-fan Wall of Wind.

Phase 2: the 12-fan Wall of Wind
Last year, Congress thought highly enough of the Wall of Wind's research results to appropriate $1 million to fund a new 12-fan Wall of Wind that will be able to generate wind speeds of 140 mph--Category 4 strength. Additional support is coming from the State of Florida. The new fans are truly massive, and it will be an impressive sight and sound when the new wall goes live. The new wall should greatly aid efforts to engineer new buildings that can withstand the winds of a major hurricane.

One other cool thing the WoW people are doing is sponsoring a Wall of Wind contest for high school students. Each year, local student compete to design a roof structure that fare the best in the Wall of Wind in some engineering category. This year, the kids had to design a roof that would minimize the amount of loose gravel that would fly off a 14x14" test roof. There were some very ingenious entries the kids designed.

Figure 2. The new 12-fan version of the Wall of Wind is currently under construction, and will be able to generate Category 4 hurricane winds of 140 mph when it is completed. Walter Conklin (left) is Laboratory Manager of the Laboratory for Wind Engineering Research, and James Erwin (right) is a research scientist studying hurricane wind damage.

The Wall of Wind website has some links to videos of the Wall in action.

I'll have a new post on Friday.

Jeff Masters


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

Category 6™


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