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Recapping the 2021 severe weather season

Lightning bolt strikes during a storm
Lightning bolt strikes during a storm(WCAX)
Published: Nov. 26, 2021 at 6:33 AM CST
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SIOUX FALLS, S.D. (Dakota News Now) -- We had a mostly dry summer across most of the area, but when we did have chances of rain, more often than not, it was accompanied by a threat of severe weather.

We reached out to the National Weather Service offices in Sioux Falls and Aberdeen to get the statistics on how the 2021 severe weather season played out and here’s what we found.

The Sioux Falls National Weather Service issued a total of 193 warnings (170 severe thunderstorm, 16 tornado and 7 flash flood). Over the past 36 years, the average number of warnings issued each year is around 262 (214 severe thunderstorm, 29 tornado, 19 flash flood)

Their most significant event of the year would have been on August 28, when 43 warnings were issued. The storms that day produced hail as big as 4″ in diameter near Larchwood and Current Lake, MN, heavy rain that prompted flash flood warnings from Sioux Falls points east towards Worthington and an EF-1 tornado that touched down in Lennox.

From April through October, there were 68 days where there was at least some sort of a severe weather risk in the Sioux Falls NWS coverage area. Of those days, 6 of those days featured an enhanced risk, which is a level three out of five.

The Aberdeen National Weather Service issued a total of 196 warnings (170 severe thunderstorm, 22 tornado and 4 flash flood). The average number of warnings issued each year is 218 (192 severe thunderstorm, 17 tornado and 9 flash flood)

Shown below is the coverage area the National Weather Service offices in Sioux Falls and Aberdeen. Both offices serve the counties in the Dakota News Now coverage area.

NWS Coverage Areas
NWS Coverage Areas(Dakota News Now)

In recent years, we have not had a severe weather risk higher than a level three out of five, minus a level 4 out of 5 risk clipping parts of central and northern South Dakota near Mobridge and Pierre back in June.

When we talk about the severe weather risk, we look at it on a scale of 0-5 (0= non severe thunderstorms, 1= marginal, 2= slight, 3= enhanced, 4= moderate, 5= high).

In fact, here’s a look at the last time each of the bigger cities in our area was under an enhanced, moderate risk and a high risk of severe weather.

Last time severe weather risk was at least three out of 5
Last time severe weather risk was at least three out of 5(Dakota News Now)

Diving in-depth a little more, here’s how many times each city has been under an enhanced, moderate and high risk of severe weather since 1987.

Number of "higher risk" severe weather days since 1987
Number of "higher risk" severe weather days since 1987(Dakota News Now)

NOTE: The enhanced risk area was introduced on October 22, 2014. Before this time, the standard risks the Storm Prediction Center used in their severe weather outlooks were slight, moderate and high.

Since the enhanced risk area was introduced, we have averaged roughly one to two enhanced risk days each year. The moderate risk days would be a little more difficult to calculate since the enhanced risk area was introduced, but it would average out to about once every couple years. The high risk days are very rare, with the average occurrence ranging from once every three years to as high as once every 15+ years.

Despite 2021 being a “below average” season, it’s always important to be weather aware during the peak of severe weather season. The peak runs from May through September, but severe weather can occur as early as March and as late as October.

It’s also always important to also have a plan in place on what to do and where you should go in case severe weather is in the forecast.

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