With about every accounting scheme now placing Iowa in the fall season, it is time to start worrying about when the first freeze will happen. Such temperatures are not far away from Iowa this Friday morning with sub freezing temperatures expected in Wisconsin. The featured chart presents an IEM analysis of the accumulated areal coverage over Iowa that has dipped below 32 degrees at least once by a given date of the fall season. This value is computed over a grid with the percentage of grid cells representing the coverage. The orange line represents the highest coverage by a given date and the green line the lowest coverage. The red line was last year's value and blue line is the simple climatology. So by the 23rd of September, at least some limited portions of the state have likely seen such cold temperatures. The 50 percent climatology value is about the second week of October, which nicely matches station climatology for a good chunk of the state.

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Tags:   firstfreeze