An area of stalled, slow-moving, and regenerating heavy thunderstorms from late on Wednesday July 1 into Thursday July 2, 2026, produced dangerous flash flooding across southeastern Minnesota.
Thunderstorms and heavy rain had affected parts of the region already on Wednesday July 1, as strong thunderstorms tracked from Colorado into Nebraska, southeastern South Dakota, and southern Minnesota. Rainfall of 1 to 1.5 inches fell from near Jackson in southwestern Minnesota, to Waseca, Rochester, and Winona. These areas were generally north and west of the areas that later would receive much heavier rain.
That heavier rain began as strong thunderstorms formed and crawled across far southeastern Minnesota late on the 1st, and into the early afternoon of July 2nd, with storms stalling and regenerating repeatedly over the same areas throughout a roughly 18-hour period. Excessive rains drenched areas from eastern Mower through Fillmore and Houston counties, leading to flash-flooding on the numerous streams within the deep valleys and hills of southeastern Minnesota. The floods in Mower County prompted water rescues at a local campground.
The heaviest rains spanned two observation dates, because most precipitation observers take their readings at 7 or 8 AM. Generally 60-80% of the rain fell before observation time on July 2nd, though it continued raining heavily at times for several more hours, with the additional rainfall tallied on the July 3rd observation. Observers in Preston, Lanesboro, Spring Valley, and Harmony all received at least six inches of rain over these two dates; during the same period, an observer in Mabel recorded 8.28 inches, with 8.19 inches in Caledonia and 8.05 inches in Grand Meadow.
Analysis of tipping bucket rainfall data from stream gauges and small airports indicates numerous locations received at least six of rain 24 hours and that in most cases 95% or more of the two-day totals fell within a 24-hour period. The area receiving 6 inches of rain or more covered over half of Houston County, about 75% of Fillmore County, and around 15% of Mower County.
The footprint of 6-inch rainfall slightly exceeds one thousand square miles, and given multiple measurements of 8 inches of rain or more, this extreme rainfall event qualifies as a rare "mega-rain," as defined by the State Climatology Office. The event marks the first such occurrence since July 25-26, 2020.
The flooding from this event was severe but not as extreme as other historical mega-rains in the area. The entire area affected had been designated "abnormally dry" on the U.S. Drought Monitor. The dry conditions likely limited the extent and magnitude of the flooding, because the dry soils required more rainfall than normal to saturate, which likely delayed and limited runoff into streams and rivers.
The State Climatology Office reminds users that the term "mega-rain" only describes the nature of the spatial dimensions and magnitude of the rainfall itself and does not guarantee a particular degree of flooding. The combination of precipitation intensity and large areal coverage do make mega-rains the most likely class of heavy rainfall events to produce disastrous or catastrophic flooding, but other factors, like existing soil moisture and topography also control flood severity. As a result, not all mega-rains have been associated with major flash floods, and not all major flash floods have been associated with mega-rains. Neither of the extraordinary, signature floods of June 2024 (one in northeastern Minnesota and one in southern Minnesota) resulted from mega-rains.
Posted July 6, 2026
KAB