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Posted at 02:25 PM ET, 05/10/2011

Mississippi River: Record rains drive record flooding

Early this morning, the Mississippi River crested at 47.79 feet in Memphis, Tennessee, 13.79 feet above flood stage and the second highest level on record. Last week, record high crest levels were reached in Caruthersivlle, Mo. and Pocahontas, Ar. Over the next several days, high waters head for the lower Mississippi river through Louisiana. So what’s behind these historic river levels? It is the extreme rainfall that inundated the central U.S. and Ohio Valley during the month of April.

NOAA reported the following yesterday in its April round-up:

The Ohio Valley region had its wettest April on record ... . Illinois, Indiana, Kentucky, Ohio, West Virginia and Pennsylvania each had their wettest April since [at least] 1895. An average of 11.88 inches of precipitation fell across Kentucky, nearly three times its long-term average, breaking the previous record (7.61 inches in 1972) by more than four inches.

Precipitation in inches over the last 30 days. (NOAA)
Over at Wunderground, Jeff Masters wrote that parts of the Ohio River Valley received as much as 20 inches of rain during the month - about half their annual average precipitation. The map above shows some of the areas, colored in white, where 20” of rain has fallen in the last 30 days. What’s even more incredible is the expansiveness of the vast area colored in pink where at least 10 inches fell from eastern Oklahoma into southern Ohio.

Joe Romm at Climate Progress discovered an eye-opening summation of rainfall records from the National Climatic Data Center, shown below (which also lists tornado and wildfire records).

(NOAA National Climatic Data Center)

While the rain in the Ohio Valley was likely the top contributor to the historic flooding, heavy snows upstream in the upper Midwest and the associated snow melt, were also a factor in the flooding.

By  |  02:25 PM ET, 05/10/2011

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