About the Indicator
This indicator looks at the length of the growing season in the lower 48 states, as well as trends in the timing of spring and fall frosts. For this indicator, the length of the growing season is defined as the period of time between the last frost of spring and the first frost of fall, when the air temperature drops below the freezing point of 32ºF.
Trends in the growing season were calculated using temperature data from 794 weather stations throughout the lower 48 states. These data were obtained from the National Oceanic and Atmospheric Administration’s National Climatic Data Center. Growing season length and the timing of spring and fall frosts were averaged spatially, then compared with a long-term average to determine the deviation from “normal” in any given year.