A severe thunderstorm developed over northcentral Iowa Tuesday afternoon and marched mostly south. This storm motion is not what we typically expect in Iowa of west to east moving storms. When the NWS issues severe thunderstorm warnings, they include a storm motion. The featured chart summarizes these storm motions issued by NWS offices with jurisdiction over Iowa. The upper chart presents a comparison between storm direction and date of year. It shows the favored direction of travel from the southwest in June to more west- northwesterly in July. The bottom chart compares storm speed with direction of travel. The fastest storms are clearly from the southwest with the largest concentration around 30 knots from the west. So our storms from the north-northwest on Tuesday are a bit rare, but not nearly unheard of like storms travelling from the east to west!

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Tags:   nws   warnings