Numerous waves of heavy, generally slow-moving thunderstorms combined to drop 2-4 inches of rain across most of southern Minnesota, with isolated areas receiving six inches of more.
The heavy rains formed near the northern edge of a warm and very humid air mass, where old and existing rain and thunderstorm complexes created a web of temperature boundaries that helped focus storm activity.
During this period, thunderstorms were scattered in both space and in time, such that different areas experienced different "events." For instance, the first heavy rains in the state occurred late on the 14th and early on the 15th, in northwestern, and also west-central Minnesota. These were different from the storms that formed later in the day toward the Twin Cities.
In general though, the event progressed as follows:
- Isolated to scattered heavy thunderstorms dropped 1-2 inches of rain over small areas of northwestern and west-central Minnesota late Thursday into early Friday.
- Later on Friday, slow-moving, heavy, and regenerating thunderstorms formed near the Twin Cities in the late afternoon, and spread southeastward slowly during the evening, producing 1-2 inches of rain, with some higher amounts.
- A large area of heavy thunderstorms then marched out of South Dakota early on Saturday, covering far more of southern Minnesota but also striking many of the same areas that had just been hit 12 hours earlier. This wave also generally produced 1-2 inches of rain.
- Late Saturday evening and into Sunday morning, heavy, regenerating, and very slow-moving thunderstorms formed near the Minnesota River and into southeastern Minnesota, with totals of 2-4 inches common in a rather narrow band, as well as isolated areas of even higher totals. Grand Meadow recorded 6.30 inches of rain, and Waseca recorded 6.00 inches, making these the two highest daily totals in Minnesota in 2025 (so far).
- On Sunday afternoon and evening, waves of heavy thunderstorms lifted northward across southern and eastern Minnesota, dropping another 0.5 to 2.0 inches of rain.
- Finally, late Sunday night and Monday morning, the final wave of scattered storms with heavy rain moved across central and southern Minnesota, with another 0.5 to 1.5 inches.
The highest rainfall total for this entire period was 9.48 inches at the Waseca Southern Research and Outreach Center (U of MN). This amount is approximately two times greater than the normal total precipitation for the month of August. The NWS Cooperative observer at Grand Meadow recorded 7.37 inches over the multi-day event. Most areas in the the southern 40% of the state had at least 2 inches of rain, with many of those areas receiving 3 inches or more.
The heavy rains prompted numerous flash flood and river flood warnings, though in general, major or extreme flooding did not occur. As of Monday August 18, many streams and rivers in southern Minnesota were either experiencing minor to moderate flooding, or were projected to do so in the days ahead.
August 18, 2025
KAB