U.S. weather in 2011: unprecedented rains and wet/dry extremes

Rains unprecedented in 117 years of record keeping set new yearly precipitation totals in seven states during 2011, NOAA's National Climatic Data Center revealed in its preliminary year-end report for 2011. An extraordinary twenty major U.S. cities had their wettest year on record during 2011. This smashes the previous record of ten cities with a wettest year, set in 1996, according to a comprehensive data base of 303 U.S. cities that have 90% of the U.S. population, maintained by Wunderground's weather historian Christopher C. Burt. Despite the remarkable number of new wettest year records set, precipitation averaged across the contiguous U.S. during 2011 was near-average, ranking as the 45th driest year in the 117-year record. This occurred because of unprecedented dry conditions across much of the South, where Texas had its driest year on record.


Figure 1. Precipitation rankings for U.S. states in 2011. Seven states had their wettest year on record, and an additional ten states had a top-ten wettest year. Texas had its driest year on record, and four other states had a top-ten driest year. Image credit: NOAA's National Climatic Data Center.


Figure 2.Wettest, driest, and warmest year records set during 2011 for major U.S. cities. No major cities had their coldest year on record during 2011. Image credit: NOAA's National Climatic Data Center.

2011 sets a new U.S. record for combined wet and dry extremes
If you weren't washing away in a flood during 2011, you were probably baking in a drought. The fraction of the contiguous U.S. covered by extremely wet conditions (top 10% historically) was 33% during 2011, ranking as the 2nd highest such coverage in the past 100 years. At the same time, extremely dry conditions (top 10% historically) covered 25% of the nation, ranking 6th highest in the past 100 years. The combined fraction of the country experiencing either severe drought or extremely wet conditions was 58%--the highest in a century of record keeping. Climate change science predicts that if the Earth continues to warm as expected, wet areas will tend to get wetter, and dry areas will tend to get drier--so 2011's side-by-side extremes of very wet and very dry conditions should grow increasingly common in the coming decades.


Figure 3. Percentage of the contiguous U.S. either in severe or greater drought (top 10% dryness) or extremely wet (top 10% wetness) during 2011, as computed using NOAA's Climate Extremes Index. Remarkably, more than half of the country (58%) experienced either a top-ten driest or top-ten wettest year, a new record. Image credit: NOAA/NCDC.

23rd warmest year on record, and 2nd hottest summer for the U.S.
The year 2011 ranked as the 23rd warmest in U.S. history, with sixteen states recording a top-ten warmest year on record. Delaware had its warmest year on record, and Texas its second warmest. However, these statistics don't convey the extremity of the summer of 2011--the hottest U.S. summer in 75 years. The only hotter summer--and by only 0.1°--was the Dust Bowl summer of 1936, when poor farming practices had turned much of the Midwest into a parking lot for generating extreme heat. The June - August 2011 average temperatures in Texas and Oklahoma were a remarkable 1.6°F and 1.3°F warmer than the previous hottest summer for a U.S. state--the summer of 1934 in Oklahoma. The U.S. Climate Extremes Index (CEI), which is sensitive to climate extremes in temperature, rainfall, dry streaks, and drought, indicated that an area nearly four times the average value was affected by extreme climate conditions during summer 2011. This is the third largest summer value of record, and came on the heels a spring season that was the most extreme on record. When averaged over the entire year, 2011 ranked as the 8th most extreme in U.S. history, since the fall weather was near-average for extremes. The CEI goes back to 1910.


Figure 4. Average temperatures for the summer in Texas and Oklahoma, at 86.8 degrees F (30.4 degrees C) and 86.5 degrees F (30.3 degrees C), respectively, exceeded the previous seasonal statewide average temperature record for any state during any season. The previous warmest summer statewide average temperature was in Oklahoma, during 1934, at 85.2 degrees F (29.6 degrees C). Image credit: National Climatic Data Center.

Wunderground's weather historian Christopher C. Burt has a more detailed look at the U.S. extremes observed during 2011 in his latest post. His selection for the most remarkable yearly record set during 2011:

Perhaps, most astonishing is the total annual rainfall of just 1.06” at Pecos, Texas (normal annual precipitation is 11.61”). If confirmed this would be a Texas state record for least amount of precipitation ever recorded in a calendar year, the current record stands at 1.64” at Presidio in 1956.

Other posts looking back at the remarkable weather events of 2011
Top ten global weather events of 2011
2011: Year of the Tornado
Deadliest weather disaster of 2011: the East African drought
Tropical Storm Lee's flood in Binghamton: was global warming the final straw?
Wettest year on record in Philadelphia; 2011 sets record for wet/dry extremes in U.S.
Hurricane Irene: New York City dodges a potential storm surge mega-disaster

I'll have a new post on Friday.

Jeff Masters