Temperatures dropped to around or slightly below freezing earlier this month across most of southern Wisconsin. This resulted in several late nights and early mornings of patchy to widespread frost, and in some cases - freezing temperatures. Only small areas near Lake Michigan from Sheboygan to Kenosha did not experience a significant frost in early October.
Since most of south-central and southeast Wisconsin has experienced two or three days of frost/freeze conditions, the National Weather Service in Milwaukee/Sullivan will no longer issue any Frost Advisories or Freeze Warnings this fall season. However, it will continue to insert wording about frost or freezing conditions in the text portion of its forecasts for the lakeshore counties of Sheboygan, Ozaukee, Milwaukee, Racine, and Kenosha until the lakeshore portions of these counties have experienced a couple days of frost/freeze conditions. Gardeners can find the text forecast in the "point and click" feature on this web site. Just click on the basemap of south-central and southeast Wisconsin on this web site to get the 7-day forecast for that point/location.
In general, when the weather is clear and calm, minimum temperatures in the mid-30s will result in frost conditions at ground level. This is due to the fact that official thermometers are postioned 5 feet above ground level. Temperatures at the ground level can easily be a few degrees colder than at th 5-foot level.
The waters of Lake Michigan take time to cool down in the fall season since the lake is large. Therefore the Lake Michigan water temperature can be 10 to 30 degrees warmer than air temperatures over land. If there is any wind off the lake it will bring warmer air inland and prevent the development of frost and freeze conditions near the shoreline. This is why, climatologically speaking, the so-called growing season usually persists until late October immediately along the Lake Michigan shoreline from Sheboygan to Kenosha.