IEM Daily Feature
Wednesday, 29 March 2023

Tornado Warning Polygon Heatmap

Posted: 29 Mar 2023 05:30 AM

Severe Weather Awareness Week continues today with the statewide tornado warning drill at 10 AM. So today's feature takes a deep dive into NWS Tornado Warnings. The NWS issues Tornado Warnings by polygon, which is a spatial area defined by latitude and longitude boundaries with only 0.01 degrees of resolution at the vertices. The featured map presents a heat map of these polygons warnings by rasterizing them onto a regular grid with each grid cell representing the number of warnings since 2008. There are many interesting artifacts shown on the map. First, you may notice a number of white slivers that have not seen a single polygon warning over this period. Second, there is an east to west frequency bias shown over counties due to an unfortunate legacy artifact of how NWS warnings are still tied to counties. NWS polygon warnings are often drawn to the county border, which implies for a storm moving generally east that the eastern portion of a county will see a higher number of warnings than the western portion. Those issues aside, some climatological "hot spots" in the state are readily apparent and likely have some physical/meteorological reasons that they exist. Being a far distance from a NWS RADAR likely decreases the chance that a NWS forecaster / RADAR algorithms can see weak tornado signatures with storms.

Good = 17
Bad = 0

Tags:   tornado