Several rounds of thunderstorms with heavy rain caused widespread, devastating flash flooding in southeast Wisconsin on the evening of August 9 through the morning of August 10, 2025. An observation of 14.55 inches of precipitation at James Madison High School in Northwest Milwaukee was reviewed by the State Climate Extremes Committee and it was determined to be a new 24-hour precipitation record for the state of Wisconsin. The previous record was 11.72 inches on June 24, 1946 near Mellen, WI in Ashland County, WI.
There is an established process to review potential new state records. The calibration and siting of the gauge was checked a few days after the event. The rain gauge data and meteorological scenario was reviewed by a committee including staff from the National Centers for Environmental Information, Midwestern Regional Climate Center, Wisconsin State Climate Office, NWS Central Region and NWS Milwaukee/Sullivan. The full report about the rainfall record is here and a table of Wisconsin records is here.
The rainfall was recorded by a Milwaukee Metropolitan Sewerage District rain gauge on the roof of James Madison High School in Northwest Milwaukee from 5 PM August 9 to 1:50 PM August 10, a 21 hour time period. The majority of the rain fell between 6 pm August 9 and 3 am August 10, 2025. Rain rates were 1 to 3 inches per hour for several hours.
Radar estimates across northwest Milwaukee ranged from 10 to 12 inches.
Many sites from the CoCoRaHS network, recorded rainfall totals of 9 to 13 inches in northeast Waukesha to northern Milwaukee county, surrounding the station providing the record, in northwest Milwaukee County. Shown are the two days totals, but the majority of this precipitation was within 24 hours.
