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.)