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Weatherwatch: May/June 2011

May 2011

The nation's severe weather nightmare continued with the deadliest individual United States tornado in 64 years. On Sunday evening, May 22, an EF-5 tornado leveled a portion of Joplin, Missouri, claiming at least 151 lives. At least 20 other individuals perished during the May 21–24 outbreak across the eastern Plains and the Mid-South. The tragic storms were in part fueled by an unusually sharp temperature contrast that led to persistently cool weather across the Northern Plains and much of the West, along with consistently above-normal temperatures in the South and East. Toward month's end, an intense, early-season heat wave built across the South, while favorable warmth overspread the Midwest. Extremely cool weather persisted, however, in California and neighboring areas. The cool conditions delayed the Western melt season, leaving substantial high-elevation snow on the ground—except in Arizona and New Mexico—past Memorial Day.

Incessantly wet conditions accompanied the cool weather across the northern Plains, triggering widespread flooding in the middle and upper Missouri Valley. In stark contrast, drought worsened across the Southern High Plains and the Deep South. By early June, the U.S. Department of Agriculture categorized at least half of the rangeland and pastures in very poor to poor condition in every southern-tier state from Arizona to Florida, excluding Alabama. Ironically, flood-control efforts extended into drought-affected areas of the lower Mississippi Valley during May, as water from the earlier inundation of the Ohio Valley and the Mid-South worked its way downstream.

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