NWS Des Moines issued a Dense Fog Advisory Tuesday morning as ample near surface moisture and calm winds promoted fog development. The Dense Fog Advisory is one of the more commonly issued alert types as shown the featured chart. The chart shows the top 25 alert types issued by NWS Des Moines since 2009 (a reliable start date for nearly all alert types). The accounting metric used here is the sum the number of counties or zones included within each alert event. For example, the aforementioned advisory covered 29 forecast zones, so that one event would have counted 29 times for this metric. The plotted values are relative to the most frequent alert type, the Severe Thunderstorm Warning. The plot attempts to show a comparable frequency with high end events like Blizzard Warning being much less common than others.

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