Greg Carbin, Warning Coordination Meteorologist at the Storm Prediction Center, recently updated his website to include maps of 2013 severe thunderstorm and tornado watches. I always like looking at these, because they highlight areas of increased and diminished severe weather threat. It’s important to not read too much into them though. As with hurricanes, it’s not always the frequency of events that makes a year memorable. 2013 was a below- or near-normal year for watches in the areas of Illinois and Indiana that were hit by a major tornado outbreak on November 17.

Tornado (left) and severe thunderstorm (right) watch count (top) and difference from 20 year average (bottom) by county. Maps are by the NOAA Storm Prediction Center and in the public domain.

Speaking of hurricanes, the quietness of the 2013 Atlantic hurricane season is evident in the below-average tornado watch count along the entire Gulf coast. Landfalling hurricanes are a major source of tornado watches for coastal states, so an anomaly in watches is often reflective of an anomaly in tropical activity. Preliminary tornado counts for 2013 are the lowest (detrended) on record. It’s not surprising, then, that the combined severe thunderstorm and tornado watch counts are generally below normal.

Severe weather watches (left) and departure from normal (right) by county. Maps are by the NOAA Storm Prediction Center and are in the public domain.

As you’d expect, Oklahoma and Kansas had the largest number of watches. What’s really interesting about the above map is the anomalously large number of watches in western South Dakota, western Montana, and Maine. Indeed, western South Dakota counties are comparable to Kansas in terms of raw watch count. Of course, that doesn’t mean the watches verified, but it’s an interesting note. Looking back through past years, the last 4 years have been anomalously high in western South Dakota. Is this an indication of a population increase, forecaster bias, or a change in severe weather climatology?