On Tuesday morning, National Weather Service Des Moines issued a Flash Flood Warning over a portion of southern Iowa due to an ongoing heavy rainfall event that brought three inches plus overnight. This warning was issued during the 6 AM hour and the featured chart today looks into the timing of the warning issuance based on text product archives dating back to 2002 for the office. The chart summarizes the number of warnings issued by hour and week of the year. The right hand side numbers present the hourly totals. The early evening hours are the most frequent time of day as late afternoon thunderstorms driven by the heating of the day have a number of hours to produce enough rainfall to lead to flooding. The early afternoon hours are the least frequent as storms are typically yet to get started by that time. The seasonality is clear as well with the largest frequencies from late May through July as storms tend to not move as quickly and thus produce larger rainfall totals over more isolated areas.

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Tags:   ffw   nwstext