Soil Temperature Data
National Weather Service
The National Weather Service North Central River Forecast Center publishes maps for soil temperatures and frost depths around the Upper Midwest.
Frost Depths in The Upper Midwest
UW Soil Science
The UW Soil Science Department also maintains up-to-date archives of climate and soil data from around the state.
Textual HYD Reports from the Co-Op Observer Network
The maps from the River Forecast Center use data from the National Weather Service's cooperative weather observation network with 700-plus observers around the state. These data are reported daily, and the NWS cautions that they have not yet been quality-controlled when first published. In the winter months, soil temperature and frost depth reports are included for a few locations around Wisconsin (scroll to the bottom of the report). You can access the latest report from the Soil Science archive, which is in a scrolling calendar format; click on the appropriate day in the calendar to see the report.