CLIMATOLOGY OF SLEET IN THE UNITED STATES

A climatology of sleet Occurrences in the United States was compiled using data for 1950-2001 from 232 weather stations. Sleet is one of the damaging forms of winter precipitation. The average annual frequency of sleet events has a latitudinal distribution east of the Rockies with values ranging from less than 1 day a year in the Deep South to 5 or more days in the north. The highest averages are 14-20 days in the northern plains. Sleet does not occur in the Florida peninsula, extreme southern Texas and Arizona, and most of the southern half of California. Most areas of the nation have had years with no sleet, but the annual minimum is 1 or 2 sleet days in the High Plains and New England. Sleet first occurs in September in the mountainous areas and the Great Lakes; in October over large parts of the nation; in November in the South; and in December along the Gulf Coast. Sleet is most frequent at night and least frequent in afternoon hours, and its average duration is 2-3 hours per event. The season's last sleet occurs in February along the Gulf Coast and shifts northward in April, the last month with sleet in most of the United States. January is the peak month for sleet incidences in all parts of the nation. The temporal distributions of sleet occurrences across the nation during 1950-1999 reveal three regions with distinctly different time distributions: northern region, southern region, and western region. Nationally, the 50-year distribution showed no up or down trend, but from 1965 to 1999 sleet events did increase, based largely on up trends in the Northeast, East North Central, and Central regions.