A Red Flag Warning was in effect yesterday for limited parts of western Iowa. These warnings are issued when dry and windy conditions create spreading fire concerns. The featured map presents the IEM computed average number of days per year with at least one hour with sustained wind speeds at or above 25 mph and relative humidity below 25%. This combination of conditions gets more rare the further east you go in the Midwest. Dry air masses originating over the desert southwest are slowly modified as they are transported east by vegetation transpiration and evaporation. Also these events are typically with strong southwesterly winds, which means the further east you go, the more likely air originated from the Gulf of Mexico (which will have high humidities).

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Tags:   firewx