The featured graph is of observed rainfall from the Rockwell City SchoolNet site. Heavy rain fell once against over Iowa last night as a slow moving cold front took its time to settle south over the state. With a tropical airmass in place, rainfall rates can become large as the storms are efficient rain producers. The rainfall rate shown on the graph is obtained by looking at 15 minute intervals of data and determining the hourly rainfall rate for those 15 minutes. You can see rates well above 3 inches per hour, which is extremely heavy for Iowa. Actual hourly rates slightly exceeded 2 inches per hour, which indicates that the extreme rates weren't sustained for the entire hour for a single location.

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