Top Ten U.S. Weather Events of 2012

It was another year of incredible weather extremes unparalleled in American history during 2012. Eleven billion-dollar weather disasters hit the U.S., a figure exceeded only by the fourteen such disasters during the equally insane weather year of 2011. I present for you now the top ten weather stories of 2012, chosen for their meteorological significance and human and economic impact.

Video 1. Hour-by-hour animation of infrared satellite images for 2012. The loop goes in slow-motion to feature such events as Hurricane Sandy, the June Derecho, Summer in March, and other top weather events of 2012. The date stamp is at lower left; you will want to make the animation full screen to see the date. Special thanks to wunderground's Deb Mitchell for putting this together!

1) Superstorm Sandy
Hurricane Sandy was truly astounding in its size and power. At its peak size, twenty hours before landfall, Sandy had tropical storm-force winds that covered an area nearly one-fifth the area of the contiguous United States. Sandy's area of ocean with twelve-foot seas peaked at 1.4 million square miles--nearly one-half the area of the contiguous United States, or 1% of Earth's total ocean area. Most incredibly, ten hours before landfall (9:30 am EDT October 29), the total energy of Sandy's winds of tropical storm-force and higher peaked at 329 terajoules--the highest value for any Atlantic hurricane since at least 1969, and equivalent to five Hiroshima-sized atomic bombs. At landfall, Sandy's tropical storm-force winds spanned 943 miles of the the U.S. coast. No hurricane on record has been larger. Sandy's huge size prompted high wind warnings to be posted from Chicago to Eastern Maine, and from Michigan's Upper Peninsula to Florida's Lake Okeechobee--an area home to 120 million people. Sandy's winds simultaneously caused damage to buildings on the shores of Lake Michigan at Indiana Dunes National Lake Shore, and toppled power lines in Nova Scotia, Canada--locations 1200 miles apart! Sandy made landfall near Atlantic City, NJ on October 29, with sustained winds of 80 mph and a central minimum pressure of 946 mb--the lowest pressure on record along the Northeast coast. The Battery, in New York City Harbor, had an observed water level of 13.88 feet, besting the previous record set by Hurricane Donna in 1960 by 3 feet. Sandy also brought torrential rainfall to the Mid-Atlantic, with over 12 inches of rain observed in parts of Maryland. In addition, Sandy generated blizzard conditions for the central and southern Appalachians with more than a foot of snow falling in six states from North Carolina to Pennsylvania, shattering October snow records. Over 130 fatalities were reported and over 8.5 million customers lost power--the second largest weather-related power outage in U.S. history, behind the 10 million that lost power during the Blizzard of 1993. Damage from Sandy is estimated at $62 billion.


Figure 1. Cabs lie flooded on October 30, 2012, in Hoboken, NJ, in the wake of Hurricane Sandy. AP photo: Charles Sykes.

2) Warmest Year on Record
Spring, March, July, and the annual temperature were all warmest on record in the contiguous U.S. July was the warmest month of any month in the 1,400+ months of the U.S. data record, going back to 1895. The spring temperature departure from average was the largest on record for any season, and March temperatures had the second largest warm departure from average of any month in U.S. history. All-time hottest temperature records were set over approximately 7% of the area of the contiguous U.S., according to a database of 298 major U.S. cities maintained by wunderground's weather historian, Christopher C. Burt. Given the very warm December temperatures so far, the final 2012 annual temperature is likely to break the previous warmest year on record (1998) by at least 0.7°F--a colossal margin to break an annual record by. It is likely that 15 states will end up with their warmest year on record in 2012, and 42 states will have a top-ten warmest year.


Figure 2. One of 2012's incredibly hot days: high temperatures on August 1 in Oklahoma from the Oklahoma Mesonet. It was the hottest day in Oklahoma since August 1936, with more than half of the state recording temperatures of 110° or higher. Oklahoma City hit 112°, tied for the city's 3nd highest temperature since record keeping began in 1890. The only hotter days occurred two days later--on August 3, 2012--and back on August 11, 1936 (113°.)

3) The Great Drought of 2012
The Great U.S. Drought of 2012 may well turn out to be the biggest weather story of 2012, since its full impacts have not yet been realized. The area of the contiguous U.S. in moderate or greater drought peaked at 61.8% in July--the largest such area since the Dust Bowl drought of December 1939. The heat and dryness resulted in record or near-record evaporation rates, causing major impact on corn, soybean and wheat belts in addition to livestock production. Drought upstream of the Lower Mississippi River caused record and near-record low stream flows along the river in Mississippi and Louisiana, resulting in limited river transportation and commerce. Crop damages alone from the great drought are estimated at $35 billion. As the total scope of losses is realized across all lines of business in coming months, this number will climb significantly.


Figure 3. Corn in Colby, Kansas withers in the Great Drought of 2012 on May 27. Image credit: Wunderphotographer treeman.

4) Wildfire Season of 2012
The 2012 U.S. fire season was the 3rd worst in U.S. history, with 9.2 million acres burned--an area larger than the state of Maryland. Since the National Interagency Fire Center began keeping records in 1960, only two years have seen more area burned--2006, when 9.9 million acres burned, and 2007, when 9.3 million acres burned. New Mexico had its largest fire in state history, Colorado its most destructive and 2nd largest in state history, and Oregon had its largest fire since the 1860s. More than 3.6 million acres burned in the U.S. during August--the most on record for any August in recorded history.


Figure 4. Wunderphoto of Whitewater-Baldy Complex Fire of 2012, the largest fire in New Mexico history. Wunderphoto submitted by AZMountaineer21.

5) March 2 - 3 Tornado Outbreak
A massive tornado outbreak of stunning violence swept through the nation's midsection March 2 - 3, spawning deadly tornadoes that killed 41 people. Hardest hit were Kentucky and Southern Indiana, which suffered 22 and 13 dead, respectively. The scale of the outbreak was exceptional, with 70 tornadoes touching down in eleven states, from southern Ohio to southern Georgia. At one point, 31 separate tornado warnings were in effect during the outbreak. An area larger than Nebraska--81,000 square miles--received tornado warnings, and tornado watches were posted for 300,000 square miles--an area larger than Texas. The outbreak spawned two EF-4 tornadoes, one which devastated Henryville, Indiana, and another that plowed through Crittenden, Kentucky. Total damage was estimated at $4 billion.


Figure 5. A school bus mangled by the EF-4 Henryville, Indiana tornado of March 2, 2012. Image credit: NWS Louisville, Kentucky.

6) June 29 Multi-State Derecho
A violent line of organized severe thunderstorms called a derecho swept across the U.S. from Illinois to Virginia on June 29, damaging houses, toppling trees, bringing down power lines. The storms killed 22 people, and left at least 3.4 million customers without power. The thunderstorms in a derecho (from the Spanish phrase for "straight ahead") create violent winds that blow in a straight line. The derecho was unusually intense due to extreme heat that set all-time records at ten major cities on the south side of the derecho. This heat helped create an unstable atmosphere with plenty of energy to fuel severe thunderstorms. At least 38 thunderstorms in the derecho generated wind gusts in excess of hurricane force, making the derecho one of the most severe derechoes on record. Total damage was estimated at $3.75 billion.


Figure 6. Turbulent clouds gather over Mettawa, Illinois on June 29, 2012, as the historic 2012 derecho begins to organize. Image credit: Wunderphotographer LarrySmit.

7) Hurricane Isaac
Hurricane Isaac slowly lumbered ashore near the mouth of the Mississippi River on August 28 as a Category 1 Hurricane with 80 mph winds. Isaac's large size and slow motion caused a storm surge more characteristic of a Category 2 hurricane--up to eleven feet--but New Orleans' new $14.5 billion levee upgrade held against Isaac's surge. The surge moved up the Mississippi River in Plaquemines Parish near Port Sulphur, causing overtopping of the levees and flooding of homes in the mandatory evacuation areas behind the levees. These levees were not part of the $14.5 billion levee upgrade. Isaac brought torrential rainfall, with more than twenty inches observed in some areas of New Orleans. Isaac also provided some drought relief to the Lower Mississippi and Ohio Valleys. Isaac dumped up to 18" of rain in Florida, and disrupted the 2012 Republican Convention in Tampa. Isaac did $2 billion in damage.


Figure 7. Tropical Storm Isaac on August 28, a few hours before it intensified into a hurricane.

8) The Non-Winter of 2011-2012
"Flowers are sprouting in January in New Hampshire, the Sierra Mountains in California are nearly snow-free, and lakes in much of Michigan still have not frozen. It's 2012, and the new year is ringing in another ridiculously wacky winter for the U.S. In Fargo, North Dakota yesterday, the mercury soared to 55°F, breaking a 1908 record for warmest January day in recorded history. More than 99% of North Dakota had no snow on the ground this morning, and over 95% of the country that normally has snow at this time of year had below-average snow cover." That was the opening of my January 6, 2012 blog post, called "Remarkably dry and warm winter due to record extreme jet stream configuration." The contiguous U.S. saw its 3rd lowest snow cover on record during both winter and spring, and the winter of 2011 - 2012 was the 4th warmest and 24th driest winter in U.S. history, going back to 1895. A primary cause of this warm and snowless winter was the most extreme configuration of the jet stream ever recorded, as measured by the North Atlantic Oscillation (NAO). The NAO index was +2.52 in December 2011, which was the most extreme difference in pressure between Iceland and the Azores ever observed in December (records of the NAO go back to 1865.) The positive NAO conditions caused the Icelandic Low to draw a strong south-westerly flow of air over eastern North America, preventing Arctic air from plunging southward over the U.S.


Figure 8. Flowers sprouting on January 1, 2012 in Keene, New Hampshire, thanks to unusually warm December temperatures and lack of snow. Image credit: Wunderphotographer lovne32.


9) April 30 - May 1 Severe Weather Outbreak
A severe weather outbreak in the Ohio Valley April 30 - May 1 caused 38 tornadoes and $4 billion in damage.

10) Late-Spring Freeze: Northeast/Midwest
After the record-warm "Summer in March" weather in the Great Lakes and Northeast, an April freeze damaged crops across the region. New York's fruit production was the lowest since 1948, and it was the worst fruit season for Michigan since 1945. Damage in Michigan alone was estimated at $500 million.



Honorable Mentions (text courtesy of NOAA's National Climatic Data Center, with damage estimates from AON Benfield):

Severe Weather Outbreak (May):
A strong cold front moving through the country on May 25 - 30 spawned 27 tornadoes from Texas to the Northeast. Damage was estimated at $2.5 billion, much of it from hail.

Severe Weather Outbreak (April):
A tornado outbreak on April 13 - 14 in the Plains spawned 98 tornadoes and caused at least 6 fatalities. Damage was estimated at $1.75 billion.

Severe Weather Outbreak (June):
Several days of severe storms across the Southwest spawned 25 tornadoes from June 6 - 12. Significant hail damage occurred across the Rocky Mountain Front Range, with total damage estimated at $1.75 billion.

Tropical Storm Debby/Wet Florida (June):
Heavy rains from Tropical Storm Debby in early June caused damage estimated at $310 million, but Debby's rains helped break a drought in Northern Florida. Florida had its wettest summer on record, partially due to Debby.

Duluth Flooding (June):
Training thunderstorms caused record flooding in and around Duluth Minnesota on June 20, with over 8 inches of rainfall observed in 24 hours in parts of the city. Two rivers in the Duluth area, the Nemadji and St. Louis, reported their highest flood heights on record. Damage was estimated at $175 million.

Pacific Northwest Winter Storm (January):
A massive winter storm impacted the Pacific Northwest on January 18 - 23. Huge amounts of rain and snow fell, and hurricane-force wind gusts knocked out power to 250,000 customers. Damage was estimated at $100 million.

Hawaiian Hail Storm (March):
On March 9, a cut-off low pressure system impacted the Hawaiian Islands, bringing heavy rainfall and severe thunderstorms. A rare EF-0 tornado hit the towns of Lanikai and Kailua on Oahu, causing minor damage. Another storm dropped a hailstone measuring 4.25 inches long, 2.25 inches tall, and 2 inches wide--the largest hailstone on record for Hawaii. Damage from the storms was estimated at $37 million.

Near-Record Low Great Lakes Levels (by end of 2012):
Record warm temperatures throughout 2012 combined with low precipitation and low winter ice cover created high evaporation rates across the Great Lakes. In December, Lakes Michigan and Huron had fallen to within inches of the all-time record low lake levels set back in 1964. Low lake levels have a significant impact on recreational and commercial boating as well as tourism.

Slow Tornado Year (annual):
Despite an active March, 2012 saw relatively low tornado numbers compared to recent history.

Mount Evans Tornado (July):
A high elevation tornado was observed along the slope of Mount Evans at 11,900 feet--the second highest observed tornado in the U.S.

Alaska Cold Winter/Snow Record (winter):
Several Alaskan locations had their coldest January on record. The monthly average temperature at Bettles, AK was -35.6°F. The statewide average January temperature was record cold--14°F below average. Record snow (134.5 inches) fell in Anchorage during the winter season, breaking the previous record set in 1954 - 55.

Alaskan Storms and Flooding (September):
Several large extratropical cyclones impacted Alaska during September. Significant flooding occurred along the Sustina River and along its tributaries, causing the worse flooding in 30 years. Over 800 structures and dozens of homes were damaged or destroyed. The storms also brought early snowfall to southern portions of the state.

Death Valley sets world record for highest minimum temperature
On Thursday morning, July 12, 2012 the low temperature at Death Valley, California dropped to just 107°F (41.7°C), after hitting a high of 128° (53.3°C) the previous day. Not only did the morning low temperature tie a record for the world's warmest low temperature ever recorded, the average temperature of 117.5°F was the world's warmest 24-hour temperature on record. According to weather records researcher Maximiliano Herrera, the only other place in the world to record a 107°F low temperature was Khasab Airport in the desert nation of Oman on June 27, 2012.

NOAA's National Climatic Data Center will release their top-ten list of U.S. weather events of 2012 on Tuesday, January 8, 2013.

Have a great holiday, everyone! I'll be back on December 26 with a new post.

Jeff Masters