Weekend tornado outbreak causes heavy damage in Virginia, Iowa

Floods, fires, and tornadoes hammered the nation this weekend, a sure sign that April is here. The severe weather action began on Friday night in the mid-Atlantic when twin tornadoes touched down in Pulaski, Virginia. The twisters, one a strong EF-1 with 105 - 110 mph winds, and the other an EF-2 with 125 mph winds damaged 450 buildings, caused $8 million in damage, and injured eight people. The most significant day of the weekend tornado outbreak occurred on Saturday as a powerful storm over the Upper Midwest dragged a cold front through Iowa. Twenty-seven tornado reports were recorded in Iowa by NOAA's Storm Prediction Center. The most powerful of these tornadoes was the huge, 3/4 mile-wide tornado that plowed through the tiny town of Mapleton, Iowa on Saturday evening, leaving a trail of destruction 3.5 miles long. The tornado, preliminarily rated as an EF-3 with 136 - 165 mph winds, flattened 20% of the town of 1200 residents and damaged half of the buildings. Fourteen were injured, but miraculously no one died. The severe weather continued on Sunday with seven reports of tornadoes over Wisconsin. The most serious was a tornado in Lincoln County, which destroyed or heavily damaged 30 buildings, and caused three serious injuries.


Figure 1. Tornado chaser video from Saturday's twisters over Iowa from tornadovideos.net.

More severe weather today
As the cold front that triggered the weekend's severe weather progresses eastwards across the U.S. today, NOAA's Storm Prediction Center has placed a wide swath of the Northeast and Southeast under their "slight" risk area for severe weather, one notch down from the "Medium" risk that was posted for Wisconsin on Sunday and Iowa on Saturday. Tuesday and Wednesday should be relatively quiet days for severe weather, but Thursday will see a renewed chance of a significant severe weather outbreak in the Oklahoma-Arkansas region, as a major new spring storm gathers strength over the Midwest.


Figure 2. Severe weather outlook from NOAA's Storm Prediction Center for Monday places much of the Northeast and Southeast in the "Slight" risk area for severe weather.

Tornado season near average so far this year
According to statistics compiled by NOAA's Storm Prediction Center, 2011's tornado season has been near-average so far. The preliminary number of tornadoes reported as of April 10 was 301, and the six-year average from 2006 - 2010 was 339. Preliminary tornado counts are typically about 15% too high, so the actual number of confirmed tornadoes will end up being around 256. The peak part of tornado season is just getting started--typically, only 17% of the season's activity has occurred by April 10. The number of strong (EF-2 and EF-3) tornadoes has been rather low so far; the Mapleton tornado was just the seventh EF-3 of 2011. There have been no violent EF-4 or EF-5 tornadoes so far this year. The death toll of just three so far in 2011 is remarkably low for mid-April, a testament to good warnings and a good helping of luck.

Jeff Masters