Under clear skies and lighter winds, temperatures fell well into the 30s over most of southern Wisconsin early this morning. In Milwaukee, where temperatures stayed a little warmer thanks to the moderating effect of Lake Michigan, the low temperature dropped to 40. This tied the record low temperature for September 15 set in 2007. Patchy frost formed in some areas, including Slinger, Hartford, Union Grove, West Bend, Merton, and Sullivan. Check out the latest Wisconsin surface plot for current temperatures.
High pressure over Minnesota will move east today and tonight. This will result in a mostly sunny day today and mostly clear skies this evening. With the high nearby tonight, surface winds will be lighter. This will allow temperatures to fall rapidly this evening, after peaking in the middle 50s to around 60 this afternoon. Temperatures will tumble into the 30s by midnight in many areas, however clouds are expected to increase over portions of southern Wisconsin during the overnight. These clouds are due to an area of showers developing in the central Plains.
The arrival of these clouds will be crucial in determining overnight low temperatures tonight and frost potential.
The coldest temperatures and best chance of frost are expected tonight along and north of a line from Portage to Beaver Dam, West Bend and inland areas of Sheboygan. This includes Green Lake, Fond du Lac and Berlin. With light winds, overnight low temperatures will dip into the 31 to 35 degree range in these areas. A frost advisory may be issued today for later tonight and early Friday. Patchy frost is possible farther south, where temperatures will be a few degrees warmer and the clouds will increase during the overnight.
The earliest date that Madison ever reached 32o (or lower) in the growing season was on September 12, 1955. Low temperatures in Madison normally do not dip down to 32o until the end of September or beginning of October.
The earliest date that Milwaukee ever reached 32 degrees (or lower) in the growing season was on September 20, 1956. Low temperatures in Milwaukee normally do not dip down to 32o until mid October.
All agricultural interests should stay abreast of the latest forecasts, and be prepared to take the necessary precautions to safeguard sensitive plants and vegetation.