Below is a handy web link to obtain current soil temperatures to determine the appropriate time to dormant seed this fall. A best practice is to look at the 10 day forecast which should play a part in deciding if the soil temps will go down or up from there. 

*We recommend dormant planting once the soil temperature stays consistently below 50 degrees Fahrenheit.

http://www.crh.noaa.gov/ncrfc/content/soilTemp/soilTempTV.php?pe=TV&depth=02