1:30 PM | Tornado threat increases tomorrow in the mid-Mississippi Valley, but so far the numbers this year are way down

Discussion

Tomorrow, the mid-Mississippi Valley will have a threat for severe storms and tornadoes and it may very well be the greatest threat of tornadoes that we have seen all year; however, the overall nationwide numbers so far this year are way down and this continues a downward trend that began a few years ago. In fact, the number of nationwide tornadoes through the end of March as reported by NOAA’s Storm Prediction Center (SPC) was 70 and this is the lowest amount in the “January through March” time period of any of the past ten years. The average number of tornadoes for the first three months of the year are 243 (based on the period from 2005-2013). The yearly nationwide tornado totals for the last two years (943 in 2013, 1119 in 2012) were the lowest annual amounts of any of the past ten years according to NOAA’s SPC.

The overriding reason for the low number of tornadoes so far this year as well as for the beginning three months of last year has to do with the fact that the persistent cold and snowy weather pattern in much of the central and eastern U.S. basically squashed the threat for severe weather. A pronounced southward dip in the polar jet stream frequently pushed cold air masses into the Gulf of Mexico and this prevented deep, moisture-laden warm air from that region to flow northward into the southern U.S. – an important, and generally necessary, ingredient for the generation of tornadoes.

As far as tomorrow is concerned, a strong upper level trough will swing out of the western states into the middle of the country and combine with an influx of warm, moisture-rich air from the Gulf of Mexico to increase the chances for severe weather and tornadoes in the mid-Mississippi Valley region. Specifically, this general threat area on Thursday will likely run from northern Louisiana to Missouri with the greatest threat perhaps centered on the state of Arkansas. The threat area for severe weather will shift eastward on Friday into the Ohio Valley albeit in a slightly weakened state.