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Map: D.C. area spends average of 45 minutes in tornado warnings every year

It’s been a quiet start to tornado season across the country, but there are signs severe thunderstorm activity will ramp up late this month and into May.

A couple weeks ago, I stumbled across the interesting infographic below, which illustrates how much time different locations spend under tornado warnings on average each year (based on the last 20 years, 1994-2013).

Note that an average tornado warning is typically 30-45 minutes long.  So locations averaging 30-45 minutes in tornado warnings are in essence averaging about one tornado warning per year.

( Iowa Environmental Mesonet)

My observations:

* A large part of the country spends a considerable amount of time in tornado warnings each year.  The central U.S. is lit up.

* Locally, we see a tornado warning hot spot in southern Maryland.  Residents of Charles County, Maryland have averaged 75 minutes under tornado warnings per year, or the equivalent of one and a half tornado warnings per year.  Most of the rest of the region is seeking shelter from possible tornadoes about 30-60 minutes per year.

* Across the rest of the country, we see tornado warning hot spots where you might expect: in the Deep South and in the Plains.

* I was surprised to see the long duration under tornado warnings along the east central coast of Florida and northeast Colorado – which I didn’t realize were such tornado-vulnerable locations.

This post presents a good opportunity to remind everyone of the difference between a tornado watch and warning:

* A tornado watch means conditions are favorable for the development of tornadoes.  Stay alert.

* A tornado warning means a tornado has been detected by radar and/or observed on the ground. Take action. (Seek shelter in a sturdy structure, in the lowest level, and put as many walls between you and the outdoors as possible.)

Jason is the Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science, and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association.
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