The Farmer's Almanac provides a frost chart for the United States on its website, Almanac.com. The chart issues average frost dates for the last spring frost for various cities.
The chart uses averages for light freeze ranging from 29 to 32 degrees Fahrenheit. Light freeze kills tender plants but does not destroy other vegetation. Local weather and topography cause variations in averages, and there is a 50 percent chance that frost occurs after the date listed.
Additionally, the Almanac's blog shares tips for predicting frost. A still night keeps cold air on the ground, while a heavy cold wind at night keeps warm air off the ground. Checking the evening weather report helps predict frost conditions.