Late Spring Freezes in the Central USA: Climatological Aspects

Abstract

Large-scale late spring freezes, herein defined as occurring more than 20 d after the median date of the last spring freeze and covering more than 30 000 sq mi, occur on average about once every 4 yr in the central USA. The areal coverage and time of occurrence of the May 1992 freeze was not remarkable compared with past freezes. The June 1992 freeze tied for the latest of this century, however. Past freezes were found to be episodic in nature and could be preceded and followed by both warm and cool conditions. The frequency distribution of summer precipitation and spring temperature and precipitation during years with late spring freezes were not significantly different from random. The summers following freezes were more likely to be cool by a statistically significant margin, however. The atmospheric circulation pattern that causes these freezes typically begins to develop a week or more before the freeze. Thus, there is the potential that forecasts of freezes can be made with some skill. The National Weather Service's 8-d forecast of daily minimum temperatures can be used to anticipate potential events and take preventive actions. Also, to aid in replanting decisions, maps showing the probabilities of growing degree day accumulations are presented for planting dates of 30 May and 15 June