The active weather patten of the past week reached its apex on Sunday, May 6th when a slow moving cool front and an upper level disturbance passed across Wisconsin. These features along with a very, moist airmass resulted in scattered to numerous slow-moving thunderstorms which produced heavy rainfall over portions of central and southern Wisconsin. Many locations received between 1 and 2 inches of rainfall in several hours time.
Morning and early afternoon thunderstorms on Sunday brought heavy rainfall to portions of south central Wisconsin. Both Madison and Fond du Lac received just over an inch of rain while Pardeeville in Columbia county received over one and a quarter inches of rain /1.34"/. The Marquette and Green Lake county areas received the heaviest rainfall during the morning. Montello received 1.44" while Princeton /1.70"/, Markesan /1.74"/ and Berlin/1.53"/ all received over an inch and a half of rain. Unfortunately, this occurred in the area where slow-moving thunderstorms dropped heavy rainfall exceeding two inches last Thursday. These repeated bouts of heavy rainfall have caused the Fox River at Berlin to exceed flood stage. Check here for the latest information on the Fox River in Berlin.
Scattered thunderstorms reformed during the late afternoon and evening over southeast Wisconsin. These thunderstorms were also slow-moving and tracked right across southern and central Waukesha and Milwaukee counties. Mitchell International Airport in Milwaukee received almost two inches of rainfall /1.86"/ between 7 pm and 8 pm CDT Sunday evening. This heavy rainfall occurring in a short period of time caused street flooding and standing water across portions of Waukesha and southern Milwaukee.
The following images show the 24-hour rainfall amounts ending around 7 am Monday, May 7, first for the NWS Milwaukee/Sullivan service area and then for the whole state of Wisconsin. The images are based on individual observations from cooperative observers and automated gauges. The observations are analyzed by a computer and used to produce a map showing values all across the area.
Now, let's look at the same kind of images, except now the accumulation period is 6 days: from the morning of May 1 until the morning of May 7.
Scattered showers are anticipated across Wisconsin on Tuesday, but then a period of dry and warmer weather is expected from Wednesday through Thursday night. This will allow some of the ponding and flood waters to recede.
National Weather Service - Milwaukee/Sullivan