Storms Could Spawn Tornadoes, Life-Threatening Flooding This Week

The final week of April will be similar to the first three, with dangerous thunderstorms over a large portion of the U.S. The forecast includes the potential for tornadoes, life-threatening flash flooding and large hail in highly populated regions from the southern Plains to the Ohio Valley and mid-Atlantic region from today through Wednesday.

Potential tornado-spawning thunderstorms will stretch from eastern Oklahoma and northern Texas to Pennsylvania today and tonight, encompassing the cities of St. Louis, Pittsburgh and Dallas. The greatest risk within this larger area appears to be in northeastern Texas, northern Louisiana and much of Arkansas, including Little Rock, according to the Storm Prediction Center.

On Tuesday, the threat of intense thunderstorms and tornadoes will extend from western New York to northeastern Texas, including the Ohio and Tennessee valleys, as well as parts of Dixie.

By Wednesday, dangerous thunderstorms are likely to develop in a significant portion of the eastern U.S., with the greatest risk for tornadoes in eastern Kentucky, Tennessee and northern Alabama. The storms will spread to the Atlantic Seaboard by Wednesday night.

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The tendency for the storms to move through regions that have already received copious amounts of rain during the month of April means that devastating flash flooding is a threat. Local amounts of 5 to 10 inches of rain are possible from today through Wednesday, resulting in rapidly rising rivers and streams, which will pose a risk to lives and property.

In response, the National Weather Service has issued numerous flood and flash flood watches and warnings along the expected path of the storms through midweek.

Rainfall amounts during the past 30 days have been two to six times greater than average, with many locations from southern Missouri to southern Ohio, as well as parts of northern Mississippi, northern Alabama and northern Georgia, having received over 10 inches of rain.

NOAA

Percentage of average precipitation in last 30 days.

The powerful thunderstorms will be sparked by upper-level disturbances moving along a very slowly moving cold front, where summer-like warmth and humidity from the south will collide with noticeably cooler, drier air to the north.

This is the same general meteorological scenario that has occurred frequently during April, a month that has generated approximately 575 tornado reports nationally and over 5,500 severe weather reports (tornadoes, wind damage and large hail).

These number are preliminary, and the actual number of tornadoes might be a little lower once the verification process has been completed.

However, the total is likely to be much higher than the three-year April average of 185. There were 139 confirmed tornadoes during all of April 2010. The most active month for tornadoes in 2010 was June, when 324 confirmed tornadoes occurred.