(National Weather Service/Des Moines) – The State of Iowa had its test tornado drill Wed., Mar 24th. In case you are wondering how common is it for a Tornado Warning to affect at least part of your county? The Iowa State University/Iowa Environmental Mesonet crunched the numbers from 2006 to 2020 to find out. (See the graphic) For many Iowans, tornadoes are the most frightening weather phenomena and something that many folks actively run practice drills for. The NWS issues a tornado warning when a tornado is observed and/or indicated to be imminent by Doppler RADAR. The featured map presents the average number of tornado warnings per year by county over the past 15 years.

Please note that the official warning presently are polygon geographies, but the counties are still used by some warning dissemination systems. Linn County (Cedar Rapids) shows up with the highest frequency on the map with other urban centers clearly visible as well. There are many complexities as to why such variability exists over the state, but distance from the nearest RADAR is an important aspect as the earth’s curvature causes the RADAR to miss the lowest parts (which are sometimes the rotating ones) as the beam travels further away from the RADAR site.