Freeze-Thaw Days in the Northeastern United States

Abstract

A freeze-thaw day is defined as a weather observation day with a maximum temperature of 0°C or above and a minimum temperature of ?2.2°C or below recorded in an instrument shelter 1.5 m above the ground. The 30 winter during 1950?80 are examined at 228 stations in nine northeastern states. Average annual freeze-thaw days range from over 90 at high elevations in the north to less than 50 along the Long Island and New Jersey shores and in the Philadelphia area. Freeze-thaw days are most common during midwinter months in the south but peak in March across inland sections. Freeze-thaw days are most numerous with average monthly temperatures between ?2°C and 0°C and approach zero at monthly temperatures below ?13°C and above 11°C. The number of freeze-thaw days with less than 7.5 cm of snow cover is about 95% of the total number along the southern coasts and less than 50% of the total in northern snowy climates. The air at 15 cm height experiences 13% more freeze-thaw days than the air at 150 cm, due to a larger daily temperature range. Hilltops experience fewer freeze-thaw days than valley bottoms.