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Explaining the severe storm risk

This is severe storm season and it’s best to be prepared and know ahead of time what storms could bring. A thunderstorm is considered severe if it contains hail 1 inch in diameter or greater, and/ or wind at 58 mph or greater and/ or a tornado. ABC17 Stormtrack meteorologists show the Storm Prediction Center severe risk in advance of thunderstorm development so you can be prepared before storms move in.

The Storm Prediction Center creates a slight, moderate, or high risk for severe weather based on probabilities. They give the probability in increments from 2% to 60%, with the higher percentage indicating the greatest probability for severe weather. These probability values represent the chance for severe weather within a 25 mile radius of a point. In Missouri, the Storm Prediction Center takes points from 16 different sites. Two of these sites are in Columbia and Jefferson City. This is why the Storm Prediction Center shades a yellow/orange/red/pink area to easily see where the greatest threat for severe weather threat is located. When it’s shaded red or pink, this is a moderate or high risk indicating a higher probability.

The importance of this when we show the ABC 17 threat tracker map. We indicate the risk along with the probabilities.

ABC 17 went back and looked at the past severe weather days we had in Mid-Missouri in 2012, 2013, and 2014. We classified a severe weather day as either large hail, strong winds, or a tornado that occurred in at least one Mid-Missouri county. In the past 3 yrs we’ve had 59 severe weather days. Of these severe weather days, we were under a slight risk 41 of those days, a moderate risk 5 days, and not under a risk, 10.

On February 28, 2012, Mid-Missouri was under a slight risk for severe weather with a 5 % probability for a tornado and a 15% probability for damaging winds and large hail. While a 5% probability seems low, multiple tornadoes broke out on this date, including an EF-2 in Phelps County that injured 35. This shows that while a 5% probability for a tornado seems low, chances are it will occur within the threat map.

On April 3 2014, areas south of I-70 were under a moderate risk for severe weather, indicating higher probabilities of 15% for tornadoes and 30-45% of damaging winds. On this date, we had one tornado touch down in Osage County, and 8 reports of damaging winds. This is important, because a 20% chance of rain is low, while a 20% probability for a tornado or damaging winds is extremely high. When the ABC 17 Stormtrack team shows a severe weather map this season, keep an eye on the threat tracker and what the probabilities are in your area.

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