Severe weather season about to begin

EF-2 tornado lifting semi trailers into the air on April 3, 2012

EF-2 tornado lifting semi trailers into the air on April 3, 2012

Nowhere on your desk calendar will it say “Severe Weather Season Begins Today”. But as our temps warm up, grass turns green, and trees sprout leaves it becomes clear severe weather season is underway.

I’ll likely write a few blog posts on severe weather in the coming weeks and months. I’ll cover any facts you may find interesting and any topics to help you prepare. But I thought it may be a good idea to get an early post out now since we MIGHT see an early onset to the season.

In Wisconsin we can get severe storms from April to September (not to say hail, high winds, or tornadoes don’t occasionally show up in other months). Even though this covers ½ the year most of our severe storms occur around the time when our daytime temps and dew points are high, but the upper atmosphere still has an active jetstream. We find this overlap typically from about mid-May to late-July. I wouldn’t be surprised to see this peak moved up a little this year. Thanks to our warm winter and mild spring (so far) the landscape is already looking green. With this early start to the growing season plants are sending water into the air through transpiration. This boost in humidity helps feeds storms that can turn severe. Often times in April we’ll see an 80 degree day with no thunderstorms because the airmass is also very dry. This particular April those arid days may not be as common. On the other hand it looks like it will be a very short fire season. Wisconsin is at its greatest wildfire risk after the snow melts but before trees, shrubs, and grass turns green.

Of course other factors come into play that effect our severe weather season (El Nino, La Nina, etc.) and these global patterns can change in a just a few weeks. Thus making a prediction as to whether or not our season will be better/worse than normal is basically a roll of the dice. Regardless of whether we face a handful of severe weather events or numerous tornado outbreaks here are a few reminders to help you understand what severe weather is and the risks.

A thunderstorm is severe if it produces:

-Straight line winds of 58 mph or greater

-Hail 1” or greater (size of a quarter)

-Tornado

A WATCH means that conditions are right for severe weather to occur. Since watches are usually issued well in advance of severe weather they may cover the entire state or parts of several states.

A WARNING means severe weather (or a tornado) has been reported by trained spotters or spotted on radar by National Weather Service meteorologists. Warnings are issued for specific storm cells and may only cover a portion of a county or a few counties.

When severe weather strikes we get on the air as soon as possible to update our viewers. But since minutes count during severe weather I highly suggest a NOAA weather radio programmed to your county. It is the quickest way to get severe weather information. Don’t wait for the sirens (topic for a later blog post)!

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