August 18-20, 2007: Southeast Minnesota
The most memorable singular event of 2007 is the southeast Minnesota flood of August 18-20, 2007. A series of thunderstorms moving along a stalled frontal boundary dropped extremely heavy rain on much of southern Minnesota beginning August 18. The most intense precipitation rates occurred during the afternoon and evening hours of Saturday, August 18, and the early morning hours of Sunday, August 19. Over the course of the event, all or portions of 28 counties received at least four inches of rain. Six-inch totals were common across the region, and portions of southeastern Minnesota reported astounding rainfall amounts ranging from 8 to 18 inches. The heaviest rainfall reports came from Winona, Fillmore, and Houston counties, where 36-hour totals exceeded 14 inches. The largest multi-day rainfall total reported was 18.17 inches observed west of La Crescent in northern Houston County. An official National Weather Service climate observer near Hokah in Houston County reported a storm total of 16.27 inches. Of the 16.27 inches, 15.10 inches fell within the observer's 24-hour observation cycle ending at 8:00 AM on Sunday, August 19. This is the largest 24-hour rainfall total ever recorded by an official National Weather Service reporting location in Minnesota. The previous Minnesota record was 10.84 inches, measured at the city of Fort Ripley in Crow Wing County on July 22, 1972.
The deluge produced flooding tied to seven fatalities. Major flood damage occurred in many southeastern Minnesota communities. Hundreds of homes and businesses were impacted. Reports of stream flooding, urban flooding, mud slides, and road closures were numerous throughout southern Minnesota. The combination of huge rainfall totals and a very large geographic extent, make this episode one of the most significant rainfall events in Minnesota's climate history. A six-inch rainfall total for a given location in this region over a 24-hour period is said to be a "100-year" (1% probability) storm. The area receiving six or more inches during a 24-hour period in the midst of this torrent encompassed thousands of square miles. Other heavy rainfall events during this decade of comparable magnitude and spatial coverage include extraordinary rainfalls in northwestern Minnesota on June 9-10, 2002 and in southern Minnesota on September 14-15, 2004.
September 6, 2007: Northeast Minnesota
On September 6, 2007 a strong weather system moving through the Midwest dropped over six inches of rain on portions of St. Louis, Lake, and Cook counties. Rainfall totals surpassed eight inches in central St. Louis County. The deluge led to overtopped and washed out sections of roads and highways. The situation was greatly tempered by the long-term drought conditions that existed prior to the rain event. A storm of this magnitude and intensity would have certainly had a greater impact had the landscape not been so dry. Another heavy rain event also affected portions of the Iron Range on September 18, 2007 when intense precipitation flooded Highway 169 near Grand Rapids.
September 20-21, 2007: West Central through East Central Minnesota
Another heavy rain event of note was one that happened on September 20-21, 2007. Intense rains doused west central and central Minnesota on September 20 and 21. Three to five inches fell along an arc that bisected Minnesota from near Ortonville to Hinckley. The rain drenched portions of Stevens, Pope, Douglas, Todd, Stearns, and Morrison counties; an area that was suffering most intensely from the 2007 drought. The rains fell hard and fast with this event in the Twin Cities. An inch of rain fell in 15 minutes at the Twin Cities International Airport. A 13 year old boy drowned after being swept over a small concrete dam in runoff-swelled Battle Creek in Battle Creek Park.