Link to the CURRENT Deep Soil Temperature Data on the National Weather Service Web site - Bismarck
Deep soil temperatures at several depths are taken at 11 NDAWN weather stations. These data are not currently available on the NDAWN web site. Daily data (averaged from hourly values) are provided here on an as-is basis. No estimates or interpolated values are available. Obvious bad data have been deleted, however more extensive quality control may be needed. See Disclaimer.
Soil Temperatures (Celsius) down to a 1170 cm (38 feet) depth are taken at one NDAWN Station:
Soil Temperatures (Celsius) down to a 175 cm (69 inch) depth from 10 North Dakota NDAWN Stations
Spring and Fall Frost Probability Dates - North Dakota probability of occurrence for spring and fall by station from the National Climatic Data Center (1981-2010).
Some files are in .pdf and can be viewed with adobe acrobat reader: 
