Extreme Spring of 2011: Jeff Masters analyzes the data and explains

Here is the first part of a very long post by Jeff Masters on the Extreme Spring of 2011 -- for the rest please go to the link below.


Nature's fury reached new extremes in the U.S. during the spring of 2011, as a punishing series of billion-dollar disasters brought the greatest flood in recorded history to the Lower Mississippi River, an astonishingly deadly tornado season, the worst drought in Texas history, and the worst fire season in recorded history. There's never been a spring this extreme for combined wet and dry extremes in the U.S. since record keeping began over a century ago, statistics released last week by the National Climatic Data Center (NCDC) reveal. Their Climate Extremes Index (CEI) looks at the percentage area of the contiguous U.S. experiencing top 10% or bottom 10% monthly maximum and minimum temperatures, monthly drought, and daily precipitation. During the spring period of March, April, and May 2011, 46% of the nation had abnormally (top 10%) wet or dry conditions -- the greatest such area during the 102-year period of record. On average, just 21% of the country has exceptionally wet conditions or exceptionally dry conditions during spring. In addition, heavy 1-day precipitation events -- the kind that cause the worst flooding -- were also at an all-time high in the spring of 2011. However, temperatures during spring 2011 were not as extreme as in several previous springs over the past 102 years, so spring 2011 ranked as the 5th most extreme spring in the past 102 years when factoring in both temperature and precipitation. 


Figure 1. Nine states in the U.S. saw their heaviest precipitation in the 117-year record during spring 2011, with record-breaking precipitation concentrated in the Pacific Northwest and along the Ohio River. Seven other states had top-ten wettest springs. Texas had its driest spring on record, and New Mexico and Louisiana had top-ten driest springs. When compared with Figure 2, we see that this is a classic winter La Niña pattern, but at extreme amplitude. Image credit: NOAA/NCDC.



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