Key Takeaways
- A new 24-hour precipitation record was set in Wisconsin with 14.55 inches of rainfall recorded at James Madison High School in Northwest Milwaukee.
- The previous record was 11.72 inches, set on June 24, 1946, near Mellen, WI in Ashland County, WI.
- The rainfall was recorded over a 21-hour period from 5 PM August 9 to 1:50 PM August 10, 2025, with the majority of the rain falling between 6 PM August 9 and 3 AM August 10, 2025.
- Rain rates were 1 to 3 inches per hour for several hours, causing widespread flash flooding in southeast Wisconsin.
- The record was verified 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.
Introduction to the Record-Breaking Event
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. The extreme weather event resulted in a new 24-hour precipitation record for the state of Wisconsin. An observation of 14.55 inches of precipitation at James Madison High School in Northwest Milwaukee was reviewed by the State Climate Extremes Committee, which determined it to be the new record. This breaks the previous record of 11.72 inches, set on June 24, 1946, near Mellen, WI in Ashland County, WI.
Verification Process
There is an established process to review potential new state records. After the event, the calibration and siting of the gauge were checked a few days later. The rain gauge data and meteorological scenario were 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. This thorough review process ensures the accuracy and validity of the record. The full report about the rainfall record is available, as well as a table of Wisconsin records, providing detailed information about the event.
Rainfall Details
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, with rain rates of 1 to 3 inches per hour for several hours. This intense rainfall caused significant flash flooding in the area, highlighting the importance of monitoring and predicting such events.
Radar Estimates and CoCoRaHS Network
Radar estimates across northwest Milwaukee ranged from 10 to 12 inches, providing additional evidence of the extreme rainfall. 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. These reports confirm the widespread nature of the heavy rainfall and flash flooding, which affected a large area in southeast Wisconsin. The data from the CoCoRaHS network and radar estimates support the record-breaking observation at James Madison High School.
Conclusion
In conclusion, the record-breaking rainfall event on August 9-10, 2025, in southeast Wisconsin resulted in a new 24-hour precipitation record for the state. The verification process ensured the accuracy of the record, and the rainfall details highlight the intensity of the event. The radar estimates and CoCoRaHS network data provide additional context and support for the record-breaking observation. This event serves as a reminder of the importance of monitoring and predicting extreme weather events, such as flash flooding, to protect lives and property.
