© 2019 Terry Swails

THE COMING SEVERE WEATHER SEASON...

March 26, 2020

This is tornado awareness week in Iowa. It's an annual event the NWS produces to say to the public, it's that time again when severe storm frequency begins to ramp up, do you have a safe plan in place if you are faced with a tornado? Surprisingly, many people don't. 

 

As you can see in this data from Craig Cogil of the NWS in Des Moines, tornado numbers in Iowa and the Midwest in general grow dramatically during April and reach their peak in June.

 

May and June account for more than 50 percent of the states twisters. In April of 2001 an outbreak produced 40 twisters, the 4th most for any individual day

The majority of Iowa's tornadoes are considered weak EF0-EF2. Even so, they can still produce winds of 65 to 135 mph.

In the graphic below you can see Iowa averages 47 twisters in an average year. Notice the small percentage that ever reach EF3-EF5 status.

The most likely time for tornadoes is during the warmest hours of the day, 1:00 to 8pm

There is a strong tendency for violent storms( EF3-EF5) to occur between 3:00 and 6:00pm...peak heating. 

An interesting fact is the stronger the tornado, the longer it's path length is likely to be. The graphic below shows the distance of Iowa's twisters on the ground. Since there are fewer "strong storms" their distance on the ground is significantly less. However, when there are strong tornadoes the atmosphere is especially prime allowing for longer path lengths.

In this graphic you can see the dates of days with the highest number of reported tornadoes.

While it's virtually impossible to predict what any severe weather season will look like in advance, I think this year has the potential to be near to above normal. The fact that a neutral southern oscillation is forecast at the peak of the season is a plus for severe weather, (La Nina) is even better.

A factor that I think increases the potential is the warm sea surface temperatures in the Gulf of Mexico and SE Atlantic. That allows moisture. latent heat, and potential ridging over the east. That would argue for an active storm track that would have some favorable dynamics to work on. Time will tell but those are a few key factors that I see as important players.

No matter what, now is a good time to get those safety plans in order. Eastern Iowa has not had a major tornado outbreak in many years and is far over due. Only 1 EF5 has touched has down east of of I-35 since 1968 and that was in Parkersburg (west of Waterloo). EF4's have been non-existent. I'm not saying this will be the year, but we are on borrowed time and the odds are growing higher every year that a major tornado outbreak will come. It's simply a matter of time!

 

On that note, a powerful storm is due in the Midwest Saturday that has the potential to produce strong to severe thunderstorms. Lots of ingredients need to be introduced into the recipe at just the right time and this being 48-60 hours away there is plenty of uncertainty on the location and overall threat. As of now, the Storm Prediction Center has this for a risk area Saturday. I could see this end up further west but for now this is what the experts are showing.

On that note, I will call it a post and live for another day. Practice those social distancing skills and roll weather...TS

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