New 24-Hour Precipitation Record Confirmed for Wisconsin

From the evening of August 9, 2025, through the morning of August 10, 2025, heavy rainfall from several rounds of thunderstorms drenched southeast Wisconsin. The Milwaukee area in particular experienced extremely high rainfall rates for hours on end. Severe and widespread urban flash flooding and river flooding led to damaged roads, homes, and businesses, as well as stranded vehicles, and necessitated numerous water rescues.

By the time the rainfall ceased at one location in Northwest Milwaukee, the final total was 14.55 inches in under 24 hours—this total was impressive enough to turn heads not just at the local level, but statewide as well.

The previous Wisconsin state 24-hour precipitation record was 11.72 inches on June 24,1946, near Mellen, Wisconsin, in Ashland County, so the local National Weather Service (NWS) office in Milwaukee/Sullivan, Wisconsin

took quick notice of the record potential of the August 9–10 rainfall event.

Setting Up for Record-Breaking Rainfall

In the Midwest, a deep layer of warm, moist air (aka as a ‘low-level jet’) provided plentiful fuel for heavy rainfall in the region leading up to the record event. A line of showers and thunderstorms passed through the area earlier in the day, resulting in a stalled front across southeast Wisconsin. The combination of the stalled front and low-level jet encouraged the development of more rounds of thunderstorms and further enhanced heavy rainfall focused on an axis in the southeast Wisconsin/Milwaukee area.

Committee Review

With enough meteorological evidence to prove the total credible, a State Climate Extremes Committee (SCEC) was comprised of local and regional NWS representatives, the Wisconsin State Climatology Office, the Midwestern Regional Climate Center, and a scientist from NOAA National Centers for Environmental Information, all of whom are stewards of the most extensive atmospheric and environmental data in the world.

An SCEC is an ad hoc group of scientists created individually for each record, and its job is to pick apart each potential record in a scientific manner. Any doubt on the part of even one member can mean a “no” vote on a record’s validity or at least trigger extensive follow-up at the record site. An extensive investigative process maintains the reputation for SCEC records to be iron-clad.

Even though the report looked promising, it was not enough to declare a new record for the SCEC. A formal assessment of the meteorology was quickly done, and the location and condition of the observation site and equipment and comparisons with surrounding stations was completed. These questions were considered:

1. Has the rain gauge been calibrated recently, and maintained properly?
2. Were there any potential obstructions to proper rainfall collection near the site, or any other reason to doubt the rainfall total?

A visit to the site to see the gauge confirmed that all calibration and maintenance checked out, and the gauge was sited in a spot with no obstructions or barriers.

Did the Observation Hold Up?

With evidence that the station was well-sited, well-calibrated, and maintained properly, and that the meteorological evidence held up to scrutiny, the SCEC verified the new Wisconsin statewide 24-hour precipitation record from the gauge at James Madison High School in Northwest Milwaukee. The new record of 14.55 inches on August 9–10, 2025 dethroned the previous state record from almost 80 years prior, a truly unusual rainfall event.

Press release submitted by the National Oceanic and Atmospheric Administration National Centers for Environmental Information.

NOTE: This press release was submitted to Urban Milwaukee and was not written by an Urban Milwaukee writer. While it is believed to be reliable, Urban Milwaukee does not guarantee its accuracy or completeness.

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