Daily Storm Based Warning Summaries

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This application displays an image summary of NWS Storm Based Warnings for a given UTC date (0z to 0z). This summary is based on an archive the IEM maintains and so is unofficial. Also, prior to 1 October 2007, these warnings were not official and their shapes may or may not have been considered by the issuing forecaster. This page works for dates between 1 Jan 2002 and 21 Nov 2024. Areas are computed and polygons shown using a US National Atlas Equal Area projection (EPSG:9311).

Related Data Links:
You can download a GIS dataset with these polygons via the GIS WWA Download. For convenience, here is a direct shapefile link with the polygons you see below. The summary size statistics page provides an overview of the size of these polygons. The actual image below was generated by Autoplot #203.

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Note: You can click on the polygon to get the warning text, radar, and more!

Image Legend:

The storm based warning is drawn with red meaning Tornado and yellow meaning Severe Thunderstorm. "422 km^2" is the size of the polygon, "73%" is the reduction in size of the warning versus the county based warning. "BMX.TO.84.2252" indicates the Forecast Office, warning type, event ID number for the year, and issuance time for the date the image is valid (22:52 UTC).
Red text indicates less than 25% reduction in size
Green text indicates greater than 75% reduction in size