Frost-Free Season

The number of frost-free days in a year reflects the overall warming trend in the climate system.
The number of frost-free days in a year reflects the overall warming trend in the climate system.

Length of the frost-free season in the U.S. is growing

During the past 30 years, there has been an increase in the length of the
frost-free season The time period between the last occurrence of an air temperature of 32°F in spring and the first occurrence of 32°F in the subsequent fall.
over the contiguous United States and Alaska, relative to the 1979–2016 average.
The bars on the graph show the difference between the number of frost-free days in each year and the average number of frost-free days from 1979 to 2016.

About Frost-Free Season

Global daily freeze-thaw data are provided by the National Aeronautics and Space Administration (NASA) Freeze-Thaw Earth Systems Data Record, which represents one of the longest continuous global records from satellite-based observations. Satellite microwave sensors are used to determine the frozen or thawed status of water on the land surface at a given time. Measurements are taken over the contiguous United States and Alaska and include all vegetated land areas where seasonal frozen temperatures are a major constraint to plant growth. Collecting these data over time provides information on the number of frost-free days in a given year.
Why It's Important
  • Observed changes in the length of the frost-free season reflect the overall warming trend in the climate system.
  • The frost-free season can be an important factor in determining the potential growing season for vegetation. For instance, some pests and pathogens affecting forests and crops are projected to benefit from warmer temperatures and longer frost-free seasons.
  • This indicator can help decision makers understand and anticipate climate impacts on:
    • Agriculture, including crop planning
    • Natural resource management
    • Wildfire
      risk management Planning to manage the effects of climate change to
      increase positive impacts and decrease negative impacts.