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Day 361: An extreme year for the United States

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Jason Samenow Jason Samenow | 09:00 UK time, Tuesday, 27 December 2011

(Jason Samenow is the Washington Post's weather editor. He founded Capitalweather.com in early 2004, the first weather blog on the web which was absorbed by the Post in 2008. He can be reached via @capitalweather)

Distance travelled ~ 927'172'800 km

A strong case can be made that 2011 was the most extreme weather year on record in the U.S. In addition to the record of at least 12 weather events that produced more than $1 billion (U.S.) in damages (totaling more than $52 billion), never has a larger percent of the country dealt with either extreme drought or abnormally heavy precipitation.

The U.S. contended with virtually every kind of weather hazard including mega snowstorms in the Midwest and Northeast, historic flooding of the Mississippi and Missouri rivers, devastating wind and flood damage from tropical weather systems (Irene and Lee) in the East, and one of the worst spring tornado seasons in memory. The tornado outbreaks that ravaged the central and southern U.S. between April and June resulted in more than 500 deaths, tied second most on record. Several exceptionally strong tornadoes struck densely populated areas including Birmingham and Tuscaloosa in Alabama as well as Joplin, Missouri.

Perhaps the most notable weather to afflict the U.S. was the devastating combination of extreme heat, drought, and wildfires in the South Central U.S. Texas was particularly hard hit. Exceptional drought gripped almost the entire state and groundwater, lake, and reservoir dropped to historic lows. The state suffered its worst wildfire season, with more than 4 million acres burned. In July, neighboring Oklahoma's average temperature was the hottest of any state in 130 years of U.S. weather records, a searing 88.9 degrees.

Undoubtedly, the moderate La Nina pattern set the stage for the unusually volatile weather conditions across the U.S. It helped fuel the powerful jet stream slicing through the middle of the country, bringing the onslaught of stormy weather. But to the south and southwest of that jet stream, a stifling heat dome blossomed and the moisture abruptly shutoff leading to historic drought.

Although global warming should not be blamed as the root cause of this punishing set of weather conditions, it very likely amplified the sharp contrasts in this pattern. The added heat in the atmosphere presumably juiced up the wet extremes by making more water vapor available, while speeding up evaporation and drying in drought areas.

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