Tornado kills one in Mississippi, but a quiet spring for tornadoes so far

Tornadoes ripped through the U.S. on Thursday for the fourth day this week, as a slow-moving spring storm brought a variety of major weather extremes across the nation. Seven preliminary tornadoes were recorded on Thursday, and one person was killed by a tornado that hit Liberty, Mississippi. Multiple injuries were reported from a tornado that hit Shuqualak, Mississippi. The strongest verified tornadoes so far from this week's outbreak were EF-2 tornadoes that hit Hazelwood, Missouri and Botkinburg, Arkansas on Wednesday, April 9.


Figure 1. A tornado roars through Noxubee County, Mississippi on Thursday, April 11, 2013. Check out this impressive video posted to Facebook of the tornado. This is probably the same tornado that killed one person near Liberty, MS.


Figure 2. Doppler velocity image of the tornado that hit Liberty, MS on April 11, 2013. The characteristic pattern of red and green colors right next to each other, showing winds moving both towards and away from the radar, show the presence of a rotating thunderstorm just north of De Kalb, MS in this image.

A quiet 2013 tornado season so far
Thursday's tornado death brought this year's tornado death toll to three, which is well below average for this time of year. According to NOAA's Storm Prediction Center, during January - March 2012, the U.S. had 60 tornado deaths. The preliminary tally for April tornadoes is 23, which is also well below average for the first eleven days of April. During the previous three years, 2010 - 2012, the U.S. averaged 368 tornadoes during the month of April. The quiet April for tornadoes follows a very quiet March; the preliminary March tornado tally of eighteen is the lowest for any March since 1978. The latest 10-year March average U.S. tornadoes through 2012 is 98. Here are the March tornado tallies below twenty tornadoes since 1950:

18: 2013
17:  1978
8:  1969
12:  1966
15:  1958
6:  1951

The reason for the low tornado numbers this spring is the unusually cool conditions that have kept instability levels low over the eastern two-thirds of the country. This has been due to a negative phase of the Arctic Oscillation (AO), which has kept a southwards-bulging portion of the jet stream in place over the eastern portion of the U.S., allowing cool air from Canada to spill southwards. NOAA's Storm Prediction Center does not have any risk areas for severe weather delineated through Sunday, but another major storm system is expected to develop over the Midwest on Tuesday, which will likely bring additional severe weather.

Jeff Masters