The featured graph looks at the frequency of hourly precipitation rates over a quarter of an inch (red bars) and the largest amount of precipitation reported during an hour (blue bars) from the Des Moines Airport since 1973. The lowest and less frequent rates occur during the 1 PM hour with maximums in the late afternoon and very early morning around sunrise. The heavy rainfall events tend to occur in the late afternoon forced by peak solar heating and early morning forced by low level jet activity. The middle of the day tends to be a lull in the forcing activity. For Iowa, peak rainfall rates usually do not exceed around 2 inches per hour.

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Tags:   climate   precip