For the month of September, the Storm Lake (NW Iowa) NWS COOP station reported just two daily rainfalls with 0.04" on the 10th and 0.42" on the 19th. So roughly 90% of the monthly total fell on just one day. The featured chart looks into the frequency of that happening with the most recent yearly occurrence shown above each bar. While generally rare, these events are most frequent during the colder half of the year when precipitation totals are lower and more easily comprised of just one big event. This situation is much more difficult during the summer months as rainfall events are more frequent and heavy rainfall events less isolated.

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