NOAA 2001-008
Contact: Pat Viets


The United States as a whole has experienced a slight decrease in the number of frost days, Dave Easterling, a climatologist with NOAA's National Climatic Data Center, told scientists at the annual meeting of the American Meteorological Society in Albuquerque, N.M., today.

Frost days, or the days when the minimum daily temperature dips below freezing, declined over the period 1948-1999, with the largest decreases in the winter and the spring. Easterling studied two questions for the 52-year period: Are there changes in the number of frost days per year or season?; and Are there changes in the dates of the first autumn frost, last spring frost, and length of the frost-free season? These questions are important to the understanding of our climate and to the agricultural community.

Changes in frost dates for autumn show little change, but the date of the last spring freeze shows a significant move to an earlier date. This results in an increase in the frost-free season. Easterling also found that there is a distinct spatial pattern to the results that is consistent with the spatial pattern of annual temperature trends for the 20th century.

This patterns shows the western United States with the largest decreases in frost days, and increases in the length of the frost-free season. But the southeastern United States, which is one of the few areas of the world showing cooling over the 20th century, has no significant changes in the numbers of frost days or the frost-free season. This should come as good news to farmers in Florida.

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