Soil moisture modeling from the University of Washington is based on the Variable Infiltration Capacity Macro-scale Hydrological Model. It includes soil moisture, snow water equivalent and runoff.
CRN soil moisture/soil temperature conditions for stations around the country are available from the National Climatic Data Center. Information is also available in the US Drought Portal CRN Soil Moisture Viewer.
Soil moisture is generally calculated based on precipitation and temperature, because the network of instrumentation to measure soil moisture is very sparse. The Natural Resources Conservation Service maintains SCAN, the Soil Climate Analysis Network. A map lets users navigate to data for each monitoring site.Click here for a brochure with more information on SCAN.
A set of maps representing changes in soil moisture for different time scales based on precipitation and temperature is available at the Climate Prediction Center web site. The model takes observed precipitation and temperature and calculates soil moisture, evaporation and runoff. The potential evaporation is estimated from observed temperature. For a description of the model used click here.
The North-American Land Data Assimilation System (NLDAS) web site has maps based on complex soil moisture models from the National Aeronautic and Space Administration (NASA) and the National Center for Environmental Prediction. The site also includes the SAC model from Office of Hydrologic Development of National Weather Service and the VIC model from Princeton University
The Climate Prediction Center soil moisture models provide output from several land surface models in a collection of several maps.