Freeze/Frost Occurrence Tables for Connecticut

1. % Probability of a later date in the spring (through July 31) than the date indicated. In other words, the percent chance that a temperature at or below the indicated threshold level will occur after the corresponding spring date.
2. % Probability of an earlier date in the fall (beginning August 31) than the date indicated. In other words, the percent chance that a temperature at or below the indicated threshold level will occur before the corresponding fall date.
3. % Probability of a longer than indicated freeze/frost-free period. In other words, the percent chance that that period of days with temperatures above the indicated threshold level will exceed the corresponding number of days listed in the table.
4. Probability of a freeze/frost day within the yearly period. In other words, the average percentage of days in the year with temperatures at or below the corresponding threshold temperature.

PLEASE NOTE: This data is intended for use as general guidelines for your location; actual frost dates vary (sometimes considerably) from year to year. Station temperature readings are commonly made at a height of approximately five feet, and actual ground temperatures can be up to 4° F to 8° F less. Thus, ground frost can occur even when the measured temperature is 36° F. Site specifics, radiational cooling, and air drainage, as well as other factors, will all have influence over actual frost dates at your location.

The preceding was excerpted from Koss, W.J. et.al. Climatography of the U.S No. 20, Supplement No. 1: Freeze Frost Data. Published by the National Oceanic and Atmospheric Administration (NOAA), 1988.