| Spring 2011 middle & lower Mississippi River Valley floods - :6981 | National Weather Service (NWS)
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Spring 2011 middle & lower Mississippi River Valley floods
  • Published Date:
    2012
Filetype[PDF-3.59 MB]


Details:
  • Corporate Authors:
    United States, National Weather Service,
  • Description:
    "The year 2011 began with extremely wet soil conditions over much of the northern plains in the north central United States. By early March, significant snow had accumulated over the same region resulting in one of the highest snow-water equivalents on record. Snowmelt and spring precipitation caused excessive runoff in much of the Ohio and Upper Mississippi River Basins by late March. The annual northward migration of warm, moist air from the Gulf Coast region following the retreat of cool, dry winter air is a rite of spring in the central United States. This event typically brings several episodes of severe weather and flooding rains, temporally and spatially, across broad reaches of the Middle Mississippi and Ohio Valleys. During the spring of 2011, the frontal zone between these two air masses moved little between April 15 and May 5. An active jet stream brought several weather disturbances eastward across the stalled frontal boundary, resulting in numerous episodes of thunderstorms accompanied by deadly tornadoes, hail, high winds, and flooding rains. The hardest hit areas stretched from eastern Oklahoma, northeast across the Middle Mississippi and Ohio River Valleys into northeastern Kentucky. As water drained into the Ohio and Mississippi Rivers, channels already full from a wet spring were unable to handle the additional runoff. The volume of water moving downstream along the Mississippi River exceeded that experienced during the 1937, 1973, and 2008 floods and caused record flooding at many points from Cairo, IL, to the Gulf of Mexico. In response to the tragic effects of this event, the National Oceanic and Atmospheric Administration's National Weather Service formed a Service Assessment Team to evaluate the National Weather Service's performance before and during the historic flooding. The findings and recommendations from this assessment will improve the quality of National Weather Service products and services, and enhance awareness of flash and river flooding"--Preface.

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