Climatological risk of strong and violent tornadoes in the United States

Knowledge of the climatological threat of severe weather is important to a wide range of risk-related interests, particularly those in the emergency preparedness and insurance communities. It can help them in the allocation of resources, and in communicating useful information to the public. We have applied spatial and temporal smoothers to the tornado dataset from The Tornado Project from 1921-1995 to estimate the daily climatological probability of an F2 or more damaging tornado occurring near any location in the United States. The Tornado Project's database contains information on more than 10,000 F2 or greater tornadoes in the United States during those 75 years. Based upon this data set, the greatest threat for strong and violent tornadoes occurs in early May in central and southern Oklahoma. We estimate that there are almost 40 days per century with strong or violent tornadoes touching down within 25 miles of any point in that region.

The southern and central Plains regions show strong seasonality in the annual cycle of tornado threat. We speculate that heightened public awareness because of this seasonality makes it easier, in some sense, for emergency managers to get the attention of the public to respond to safety messages. This contributes to the result, with other factors, including demographics, that tornadoes in this region tend to be less deadly than in other parts of the country, despite the greater risk of event occurrence.

These results are part of an effort to establish an accessible database with climatological threats of severe weather for every location in the country for every day of the year.