A moisture-heavy air mass unloaded torrential rains for a period of 6-12 hours across a large swath of southern Minnesota from the evening of Saturday July 25th into the morning of Sunday July 26th.
The thunderstorms formed in an air mass that contained some the highest total moisture measured in southern Minnesota this season. The 2.25 inches of "precipitable water" tallied from the 7 PM weather balloon launch at Chanhassen was just below record record levels for the day and was above the 95th percentile for this time of year. The excessively humid air mass led to dew point temperatures in the middle and upper 70s throughout Minnesota by Saturday afternoon.
Showers and thunderstorms on the morning of the 25th had left a patchwork of clouds and minor boundaries all over Minnesota. Where the sun could peek out of the clouds, temperature rose to near 90 F or higher, but generally remained in the 80s elsewhere. The winds aloft were weak, and the only real cold front was just creeping into far northwestern Minnesota on Saturday afternoon. The stage was set for prolonged intense rains somewhere in Minnesota, but it was unclear exactly where the storms would form.
The main event began as a large thunderstorm developed over Sibley County just after 5 PM. The storm intensified rapidly, and produced a confirmed tornado near Gaylord around 630 PM. With nothing to steer it or drive it away, the thunderstorm moved little while expanding eastward slowly and "back-building" to the west. The thunderstorms reached into the southern Twin Cities metropolitan area by mid-evening, but they remained anchored over the same areas of Renville, Sibley, and Le Sueur Counties even as darkness fell. The growing but almost stationary storm complex produced vivid lightning, nearly constant thunder, and spectacular late-evening optics, even in areas that received little or no rainfall.
By 9 PM, heavy rains had been falling continuously for 2-4 hours from near Fairfax in Renville County to Gibbon and Winthrop in Sibley County, and over into much of Le Sueur County. The thunderstorms eventually pushed southeastward into Nicollet, Blue Earth, Waseca, and Rice Counties, but as they did were replaced quickly by new storms that resumed lashing the areas that had already been drenched by earlier rains. The National Weather Service in Chanhassen had issued Flash Flood Warnings for a multi-county swath of southern Minnesota.
Even at 3 AM, new strong thunderstorms were forming in southwestern and western Minnesota, as the surge of deep moisture into the region continued, and as the cold front inched its way eastward across the state. The heaviest rains began winding down after sunrise, but moderate rains persisted in some areas through 8 AM.
The expansive, regenerating, and long-lasting intense thunderstorms activity resulted in a wide swath of very high precipitation totals. Automated rain gauges and human observers in six different counties reported rainfall totals of six inches or greater.
The highest known total for the storm came from near Winthrop in Sibley County, where a volunteer observer for the county reported 11.50 inches. Other high totals in that area included 10.70 inches near Lafayette, and 9.15 inches in Gibbon. These amounts are near or exceed the 500-year threshold for 24-hour rainfall in that part of Minnesota.
Southeast of the area of most extreme rainfall, a CoCoRaHS observer just south of Mankato, reported 8.65 inches. Other totals of 8 inches or more were found in the area, with numerous 6-7-inch reports near St. Clair, St. Peter, Kasota, and Morristown. A DNR automated rain gauge at Fort Ridgely State Park recorded 7.77 inches, with the same type of equipment reporting 6.37 inches in Morristown. These values are likely "under-catches" by up to 10%, because automated tipping buckets cannot keep up with intense rainfall rates. The State Climatology Office thanks all of the volunteer observers whose reports added significant information about the extent and magnitude of this major event.
This storm produced six inches of rain or more over an area of roughly 1000 square miles, making this event the first "mega-rain" since 2016. Apart from water covering roads and filling many ditches, however, this event produced little in the way of major damages. Most rains of this magnitude produce landslides, wash out roads, and damage public and private property, but fortunately, this one came when river levels had been relatively low, and when area soils had been in good condition after a mostly "normal" summer.
Following is a round-up of rainfall reports from the National Weather Service office in Chanhassen.
Public Information Statement National Weather Service Twin Cities/Chanhassen MN 1006 AM CDT Sun Jul 26 2020 ...July 25-26 Heavy Rain Event... Location Amount Time/Date Provider ...Minnesota... ...Anoka County... Ramsey 3NE 1.05 in 0837 AM 07/26 COCORAHS ...Benton County... Sauk Rapids 1.27 in 0957 AM 07/26 CWOP Rice 3.8 SSE 1.27 in 0700 AM 07/26 COCORAHS ...Blue Earth County... Mankato 3.3 SSW 8.65 in 0800 AM 07/26 COCORAHS Skyline 2ESE 8.63 in 0700 AM 07/26 COCORAHS Mankato 0.2 SSW 7.93 in 0600 AM 07/26 COCORAHS Mankato 1ESE 7.75 in 0700 AM 07/26 COCORAHS Mankato 1.2 SE 7.38 in 0700 AM 07/26 COCORAHS Mankato 2.9 WSW 7.30 in 0800 AM 07/26 COCORAHS Mankato 4.0 SW 7.05 in 0815 AM 07/26 COCORAHS St. Clair 6.96 in 0645 AM 07/26 HADS Eagle Lake 0.4 SW 6.90 in 0700 AM 07/26 COCORAHS Mankato 1.3 SW 6.74 in 0600 AM 07/26 COCORAHS Mankato 6.4 S 6.69 in 0700 AM 07/26 COCORAHS Mankato 2.2 NNE 6.58 in 0804 AM 07/26 COCORAHS 4.5 SE Skyline 6.08 in 0900 AM 07/26 HADS 4.6 NE Good Thunder 5.98 in 0900 AM 07/26 HADS Garden City 2.7 WSW 5.87 in 0750 AM 07/26 COCORAHS 4.4 NE Good Thunder 5.47 in 0900 AM 07/26 HADS Mankato AP 5.38 in 0956 AM 07/26 AWOS 1.6 W Garden City 5.21 in 0930 AM 07/26 HADS Mapleton 4N 4.55 in 0830 AM 07/26 COCORAHS Lake Crystal 4.9 N 4.30 in 0630 AM 07/26 COCORAHS 4.8 S Good Thunder 3.19 in 0900 AM 07/26 HADS ...Brown County... New Ulm 0.2 SSW 5.01 in 0800 AM 07/26 COCORAHS Sleepy Eye 0.8 SW 2.87 in 0800 AM 07/26 COCORAHS Comfrey 2.52 in 0955 AM 07/26 CWOP 4.6 SE Cobden 2.21 in 0830 AM 07/26 HADS Springfield 1NW 1.92 in 0700 AM 07/26 COCORAHS Springfield 1.89 in 0946 AM 07/26 CWOP 4.3 SW Springfield 1.66 in 0930 AM 07/26 HADS 3.1 SE Cobden 1.01 in 0900 AM 07/26 HADS ...Carver County... Watertown 0.5 NNW 2.07 in 0700 AM 07/26 COCORAHS 1.9 NW Jordan 1.66 in 0930 AM 07/26 USGS Waconia 0.7 WNW 1.39 in 0800 AM 07/26 COCORAHS Waconia 1.38 in 0700 AM 07/26 UCOOP Carver 3S 1.28 in 0949 AM 07/26 RAWS Waconia 1WSW 1.20 in 0959 AM 07/26 AWS ...Chippewa County... 8 NE Watson 1.20 in 0955 AM 07/26 AWS Raymond 4.7 WSW 1.10 in 0800 AM 07/26 COCORAHS ...Chisago County... Scandia 1.47 in 1000 AM 07/26 CWOP Wyoming 1.07 in 0956 AM 07/26 CWOP ...Dakota County... Northfield 1NNW 2.00 in 0930 AM 07/26 COCORAHS Farmington 3E 1.52 in 0800 AM 07/26 COCORAHS West Saint Paul 1.2 NE 1.48 in 0800 AM 07/26 COCORAHS Farmington 2ESE 1.40 in 0935 AM 07/26 COCORAHS 4.4 SE Lakeville 1.40 in 0815 AM 07/26 HADS Inver Grove Heights 1.6 NE 1.35 in 0751 AM 07/26 COCORAHS Hastings 0.7 S 1.25 in 0600 AM 07/26 COCORAHS Lakeville 2.1 N 1.25 in 0815 AM 07/26 COCORAHS Hastings 1.6 NW 1.21 in 0700 AM 07/26 COCORAHS Farmington 1.12 in 0700 AM 07/26 UCOOP Miesville 2WSW 1.11 in 0700 AM 07/26 COCORAHS Lakeville AP 1.07 in 0955 AM 07/26 AWOS 2.6 SW Coates 1.03 in 0900 AM 07/26 HADS Hastings 1.00 in 0530 AM 07/26 COOP ...Faribault County... Minnesota Lake 3.56 in 0946 AM 07/26 CWOP Winnebago 2.20 in 0713 AM 07/26 COOP Wells 2.11 in 0946 AM 07/26 CWOP Wells 3.5 SE 2.10 in 0900 AM 07/26 COCORAHS Elmore 1N 1.88 in 0700 AM 07/26 COCORAHS Frost 0.3 ENE 1.45 in 0700 AM 07/26 COCORAHS Blue Earth 0.6 ESE 1.44 in 0700 AM 07/26 COCORAHS 0.6 W Blue Earth 1.31 in 0615 AM 07/26 HADS 0.7 N Blue Earth 1.21 in 0615 AM 07/26 HADS Bricelyn 1.01 in 0700 AM 07/26 COOP ...Freeborn County... Albert Lea 1WSW 2.32 in 0700 AM 07/26 COCORAHS ...Goodhue County... 3 ENE Dennison 1.76 in 0955 AM 07/26 AWS Cannon Falls 2S 1.44 in 0915 AM 07/26 HADS Dennison 0.4 SSE 1.43 in 0700 AM 07/26 COCORAHS 7.0 S Cannon Falls 1.43 in 0900 AM 07/26 HADS Red Wing 1.37 in 0955 AM 07/26 CWOP Cannon Falls 5.6 ESE 1.37 in 0830 AM 07/26 COCORAHS Dennison 2.0 NNE 1.33 in 0700 AM 07/26 COCORAHS Nerstrand 4E 1.30 in 0700 AM 07/26 COCORAHS Cannon Falls 0.5 SE 1.29 in 0800 AM 07/26 COCORAHS Red Wing 1.22 in 0945 AM 07/26 CWOP Stanton AP 1.20 in 0955 AM 07/26 AWOS 4.4 S Maiden Rock 1.18 in 0830 AM 07/26 HADS 3.5 SW Maiden Rock 1.18 in 0830 AM 07/26 HADS Zumbrota 1.12 in 0958 AM 07/26 CWOP Vasa 5NNE 1.12 in 0700 AM 07/26 COCORAHS Zumbrota 0.6 SSE 1.10 in 0952 AM 07/26 COCORAHS Red Wing 3SE 1.08 in 0700 AM 07/26 COCORAHS Cannon Falls 0.7 SSW 1.08 in 0700 AM 07/26 COCORAHS Dennison 6E 1.05 in 0700 AM 07/26 COCORAHS Wanamingo 4SSE 1.03 in 0800 AM 07/26 COCORAHS ...Hennepin County... Crystal AP 1.08 in 0953 AM 07/26 ASOS Minneapolis 3.6 SSE 1.00 in 0900 AM 07/26 COCORAHS ...Kandiyohi County... Pennock 6NNE 1.93 in 0700 AM 07/26 COCORAHS New London 6WSW 1.25 in 0700 AM 07/26 COCORAHS 2 NW Pennock 1.17 in 0955 AM 07/26 AWS 5 SW Atwater 1.15 in 0955 AM 07/26 AWS 4.7 W New London 1.00 in 0915 AM 07/26 HADS ...Lac qui Parle County... Madison 3.6 NW 1.13 in 0800 AM 07/26 COCORAHS ...Le Sueur County... 2.6 SW Kasota 6.25 in 0900 AM 07/26 HADS 3 N Madison Lake 3.74 in 0955 AM 07/26 AWS Le Center 5NNW 2.82 in 0800 AM 07/26 COCORAHS New Prague 1ESE 2.55 in 0725 AM 07/26 COCORAHS Montgomery 3E 2.45 in 0700 AM 07/26 COCORAHS Montgomery 2.1 N 2.24 in 0800 AM 07/26 COCORAHS New Prague 1.0 S 1.86 in 0700 AM 07/26 COCORAHS ...Martin County... 4 N Ceylon 1.34 in 0920 AM 07/26 AWS 6 SSE Granada 1.34 in 0955 AM 07/26 AWS Fairmont 0.7 E 1.34 in 0700 AM 07/26 COCORAHS Fairmont AP 1.30 in 0956 AM 07/26 AWOS 3 NNE Granada 1.12 in 0955 AM 07/26 AWS ...McLeod County... Brownton 1.58 in 0845 AM 07/26 HADS Brownton 0.2 SSE 1.30 in 0800 AM 07/26 COCORAHS ...Mille Lacs County... Milaca 2.18 in 0951 AM 07/26 CWOP Foreston 1.80 in 0956 AM 07/26 CWOP Foreston 2.1 NW 1.77 in 0645 AM 07/26 COCORAHS 1.3 NW Princeton 1.05 in 0900 AM 07/26 HADS Princeton AP 1.02 in 0955 AM 07/26 AWOS ...Nicollet County... 4.9 S Fairfax 7.77 in 0615 AM 07/26 HADS North Mankato 0.8 SSW 7.50 in 0730 AM 07/26 COCORAHS Saint Peter 0.6 NW 6.95 in 0800 AM 07/26 COCORAHS Kasota 4WSW 6.71 in 0700 AM 07/26 COCORAHS 0.6 E St. Peter 6.67 in 0900 AM 07/26 UCOOP St. Peter 6WSW 6.57 in 0700 AM 07/26 COCORAHS St. Peter 6.52 in 0600 AM 07/26 COOP 3.7 SW Kasota 5.89 in 0900 AM 07/26 HADS Judson 5.74 in 0800 AM 07/26 UCOOP Nicollet 4.98 in 0958 AM 07/26 CWOP New Ulm 3SE 4.52 in 0700 AM 07/26 COOP North Mankato 3.81 in 1000 AM 07/26 AWS ...Pope County... 8 WNW Sunburg 1.16 in 0955 AM 07/26 AWS ...Ramsey County... St. Paul Dwtn AP 1.31 in 0953 AM 07/26 ASOS 3 S Maplewood 1.05 in 1000 AM 07/26 AWS St. Paul 1N 1.00 in 0800 AM 07/26 COCORAHS ...Redwood County... Redwood Falls 0.6 NE 5.39 in 0700 AM 07/26 COCORAHS 1.1 NE Lamberton 4.75 in 0900 AM 07/26 HADS Redwood Falls 2.82 in 0700 AM 07/26 COOP Redwood Falls AP 2.64 in 0953 AM 07/26 ASOS Lamberton 2.05 in 0956 AM 07/26 CWOP Belview 0.3 S 1.92 in 0630 AM 07/26 COCORAHS Wabasso 3E 1.76 in 0800 AM 07/26 COCORAHS ...Renville County... Fairfax 4.9 SSE 8.00 in 0700 AM 07/26 COCORAHS Bird Island 7SSE 3.27 in 0800 AM 07/26 COOP Bird Island 7SSE 3.27 in 0800 AM 07/26 COCORAHS Morton 2.59 in 0845 AM 07/26 HADS Delhi 5NE 2.20 in 0700 AM 07/26 COCORAHS Bird Island 0.3 SW 2.02 in 0650 AM 07/26 COCORAHS Danube 2WNW 1.79 in 0700 AM 07/26 COCORAHS 4.1 W Sacred Heart 1.44 in 0845 AM 07/26 HADS Sacred Heart 5.8 S 1.15 in 0700 AM 07/26 COCORAHS Lake Lillian 5SE 1.05 in 0830 AM 07/26 COCORAHS ...Rice County... Morristown 6.37 in 0815 AM 07/26 HADS Faribault 1.6 S 3.29 in 0700 AM 07/26 COCORAHS Faribault 3.28 in 0957 AM 07/26 CWOP Faribault 1SSW 3.11 in 0959 AM 07/26 AWS Faribault 1.7 N 3.07 in 0800 AM 07/26 COCORAHS Faribault 1.1 E 2.95 in 0800 AM 07/26 COCORAHS Faribault 3.5 ESE 2.83 in 0700 AM 07/26 COCORAHS Veseli 2E 2.30 in 0700 AM 07/26 COCORAHS Montgomery 3ENE 1.97 in 0600 AM 07/26 COCORAHS Northfield 3.9 SSW 1.75 in 0700 AM 07/26 COCORAHS Northfield 1.50 in 0845 AM 07/26 UCOOP Northfield 2.1 SSW 1.42 in 0715 AM 07/26 COCORAHS Northfield 1.2 ESE 1.38 in 0700 AM 07/26 COCORAHS Veseli 1W 1.25 in 0500 AM 07/26 COCORAHS Northfield 0.4 NW 1.25 in 0600 AM 07/26 COCORAHS ...Scott County... New Prague 1.0 NNW 2.22 in 0700 AM 07/26 COCORAHS Jordan 1SSW 2.20 in 0530 AM 07/26 COOP New Prague 3.8 NE 1.92 in 0745 AM 07/26 COCORAHS New Prague 0.9 NNE 1.90 in 0638 AM 07/26 COCORAHS 2 WNW Elko New Market 1.78 in 0955 AM 07/26 AWS Jordan 4.2 SSE 1.65 in 0800 AM 07/26 COCORAHS Lydia 1.32 in 0946 AM 07/26 CWOP Lakeville 1.17 in 0956 AM 07/26 CWOP Shakopee 1NW 1.16 in 0957 AM 07/26 CWOP ...Sherburne County... Elk River 2.58 in 0950 AM 07/26 CWOP Elk River 3.2 W 1.72 in 0700 AM 07/26 COCORAHS Elk River 1.6 S 1.59 in 0700 AM 07/26 COCORAHS ...Sibley County... 4 E Gibbon 7.64 in 0955 AM 07/26 AWS Gibbon 6.61 in 0946 AM 07/26 CWOP ...Stearns County... 1.4 NW St. Martin 1.78 in 0845 AM 07/26 HADS Clearwater 3.2 SW 1.54 in 0800 AM 07/26 COCORAHS Belgrade 0.4 WNW 1.45 in 0900 AM 07/26 COCORAHS Sauk Centre AP 1.17 in 0955 AM 07/26 AWOS Kimball 3N 1.12 in 0600 AM 07/26 COOP Sartell 2.6 SW 1.00 in 0800 AM 07/26 COCORAHS ...Steele County... Hope 4.18 in 0958 AM 07/26 CWOP Owatonna 1.8 SSE 3.89 in 0630 AM 07/26 COCORAHS Owatonna 1.5 S 3.59 in 0700 AM 07/26 COCORAHS Owatonna 3.31 in 1000 AM 07/26 AWS Owatonna 1.0 ENE 3.15 in 0710 AM 07/26 COCORAHS Owatonna 0.8 E 2.94 in 0700 AM 07/26 COCORAHS 1.9 NE Owatonna 2.92 in 0845 AM 07/26 HADS Ellendale 0.3 SW 2.35 in 0700 AM 07/26 COCORAHS Owatonna 2.20 in 0800 AM 07/26 COOP ...Swift County... 1.2 W Benson 1.37 in 0715 AM 07/26 HADS ...Waseca County... Morristown 2SW 5.35 in 0651 AM 07/26 COCORAHS Waseca 6.0 N 5.28 in 0800 AM 07/26 COCORAHS Waseca 1NNE 4.81 in 0700 AM 07/26 COCORAHS Waseca 2.0 N 4.70 in 0700 AM 07/26 COCORAHS Waseca AP 1.13 in 0459 AM 07/26 AWOS ...Washington County... 2 ENE Mahtomedi 2.15 in 0955 AM 07/26 AWS Stillwater 1.98 in 0955 AM 07/26 CWOP Stillwater 2 SW 1.94 in 0900 AM 07/26 COOP Woodbury 1.30 in 0741 AM 07/26 CWOP Afton 1E 1.29 in 0850 AM 07/26 COCORAHS Denmark Township 1.28 in 0950 AM 07/26 CWOP 3 NNE Stillwater 1.27 in 0955 AM 07/26 AWS Stillwater 0.8 SW 1.25 in 0725 AM 07/26 COCORAHS Lakeland 1.8 S 1.20 in 0920 AM 07/26 COCORAHS Forest Lake 1SE 1.17 in 0959 AM 07/26 AWS Lakeland 1.15 in 0955 AM 07/26 CWOP Stillwater 0.2 E 1.12 in 0615 AM 07/26 COCORAHS Stillwater 5.7 SSE 1.07 in 0754 AM 07/26 COCORAHS ...Watonwan County... 2 N Madelia 4.04 in 0955 AM 07/26 AWS Madelia 3.87 in 0950 AM 07/26 CWOP Saint James 0.5 SSW 3.65 in 0700 AM 07/26 COCORAHS 2.9 W Madelia 3.64 in 0745 AM 07/26 HADS 3.5 E La Salle 3.27 in 0830 AM 07/26 HADS ...Wright County... Clearwater 4SE 2.00 in 0700 AM 07/26 COCORAHS Clearwater 1.87 in 0915 AM 07/26 HADS Delano 1.70 in 0730 AM 07/26 HADS Maple Lake 1.22 in 0945 AM 07/26 CWOP Winsted 1.22 in 0956 AM 07/26 CWOP Golden Valley 1.20 in 1000 AM 07/26 CWOP Monticello 1.18 in 0958 AM 07/26 CWOP Otsego 1.8 ENE 1.08 in 0748 AM 07/26 COCORAHS 4.0 NE Cokato 1.00 in 0945 AM 07/26 HADS ...Yellow Medicine County... Granite Falls 1.51 in 0900 AM 07/26 UCOOP 4.4 S Hazel Run 1.21 in 0900 AM 07/26 HADS Observations are collected from a variety of sources with varying equipment and exposures. We thank all volunteer weather observers for their dedication. Not all data listed are considered official.
Modified July 27, 2020