Radar mosaic animation showing large area of rain affecting much of the Upper Midwest on Tuesday May 20, 2025.
Radar loop courtesy of College of DuPage; data from NOAA/National Weather Service
A prolonged and widespread rainfall event soaked all but the northeastern third of Minnesota with 1 to 3+ inches of rain, from Monday May 19 through Wednesday May 21, 2024.
The rain fell in association with a strong low-pressure system that passed south of Minnesota, tracking from Wyoming, through Nebraska and Iowa, before weakening in Illinois. The system was responsible for multiple rounds of severe thunderstorms across the Plains and lower Mississippi River valley. Minnesota was on the cooler side of the circulation, but remained in a sustained flow of moisture that led to copious precipitation.
The rain fell in three distinct phases. First, scattered thunderstorms with brief downpours developed across the southern half of Minnesota on Monday afternoon and evening, generally ending around 11 PM. Next, a large area of steady rain with strong winds spread northward and eventually westward across most of central and southern Minnesota from around midnight through most of Tuesday. being on the north side of the strong low pressure centered in Iowa, the precipitation exhibited regional cyclonic (counter-clockwise) circulation. As the main forcing for precipitation moved out of the region late Tuesday, the third phase began, with narrow bands of light to moderate rain streaking across parts of the state, with drizzle and mist in between. This phase dropped the least precipitation but lasted the longest, with parts of central and eastern Minnesota seeing rain and drizzle until late Wednesday evening or early Thursday morning.
Soaking rains covered all but the northeastern part of the state, with totals of an inch or more generally affecting areas along and southwest of a line from Thief River Falls, to Aitkin, to Hinckley. Rainfall totals of 2 to 3.5 inches were common in about half of that areas, including the I-94 corridor, the Minnesota River, the entire Twin Cities area, and Rochester. This is equivalent to between 60 and 90% of normal precipitation for the entire month of May.
Oddly, the same pattern that blew moisture into the central and southern parts of Minnesota, also blew dry air into northern areas on Tuesday. Relative humidity plunged to 25% or lower in some parts of northeastern Minnesota, and combined with strong and gusty winds to create elevated wildfire hazards. In response, the National Weather Service issued Red Flag Warnings for the Arrowhead region. The strong, dry winds also blew some limbs down, causing thousands of power outages in the Duluth area alone.
May 21, 2025
KAB