Severe Weather Awareness Week: Tornado Frequency - KMSP-TV

Severe Weather Awareness Week: Tornado Frequency

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It is Severe Weather Awareness Week in Minnesota and Wisconsin.  This week is dedicated to reminding ourselves about the dangers of severe summer weather and what we can do to be prepared in case we have to act.  Severe summer weather can be anything ranging from Tornadoes and destructive winds, to flash flooding, drought, and heat waves.  In many cases, every single Minnesotan sees some form of severe weather every summer.  It doesn’t always cause damage or injuries, but if you aren’t prepared and don’t use a little knowledge and common sense when crossed by Mother Nature, then you may just end up in a situation that you don’t want to be in.

Clearly the most obvious and talked about severe weather phenomena are tornados so we might as well start there.  Minnesota averages 45 tornadoes a year with Wisconsin coming in with about half that at 24.  But years can vary greatly from just a couple to well over 100.  The images below are from Iowa State and they tell us a lot about how often we have to deal with this type of severe weather nationwide, from when the average first tornado warning is issued to the typical peak of tornado season, to average number of tornado watches… so check them out below.

First off, the following 5 images show stats based on the National Weather Service County Forecasting Areas.  These are the separate zones that each NWS office forecasts for.  These same offices are the ones that issue the warnings during severe weather.  Let’s start with when the average first tornado warning is issued.

For the NWS office in Chanhassen, the first tornado warning is typically issued on May 12th.  Peak season though arrives a little later.

The metro typically sees the most tornado warnings issued during the week of June 24th, barely 6 weeks after the average first warning, so the season ramps up quickly.  So how many tornado warnings are issued every year?  Well from January 2005 to now, more than 400 tornado warnings were issued by the National Weather Service office in Chanhassen. On average, that’s about 45 a year.  Sound like a lot??  Look to the southeast U.S. where forecast offices have issued 3 or 4 times that many warnings since 2005.

Want to know how many minutes your county is typically involved in a tornado warning?  Well, there’s an app for that… ok not really, but find your county in the picture below.

For example, Hennepin County spends an average of 45-60 minutes a year in a tornado warning.  That would be the length of an average of 2 tornado warnings, of course depending upon the storm.  Larger counties will often spend more time in warnings like you see with Stearns County who spends 90-120 minutes a year in a warning… about double that of our west metro counties.  Just look at the southeast U.S. though.  Some counties spend more than 240 minutes, or 4 hours a year in a tornado warning… ouch!

And finally, how many tornado watches are issued for each county during the year?  Well, just look below.

According to the Storm Prediction Center, metro area counties average 5 tornado watches a year, well at least according to the stats from 1999-2008.  Sound like a lot? Not when you compare it to the Gulf Coast with southern Mississippi and Alabama averaging 3 times more a year, 16 to be exact.  This is why many Meteorologists believe there are now 2 different tornado allies called Tornado Alley and Dixie Alley.  That will be explained in a future blog post.

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