NWS Sioux Falls issued a Red Flag Warning (Fire Weather) Wednesday for its forecast area, which includes a number of Northwestern Iowa counties. The featured chart looks into the duration of these warning events based on the office's warnings since 2006. The plotted lines represent the accumulated frequency of warning events at a given time duration value. An event is a single warning for a single county / forecast zone. The plot nicely shows these events are generally between four and eight hours in duration, which covers the windiest and least humid portion of the daylight day. Shorter duration events are typically covered by other messaging, like the Special Weather Statement and longer duration events are typically not possible with subsiding winds as the boundary layer stabilizes, cools, and increases with humidity.

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Tags:   firewx