Earlier this month we looked out the window and it was snowing, but our yard thermometer read 40 degrees. How can that be?
Rich Escallier, Chicago
It can snow when temperatures are above 40. Snow has fallen in Chicago with temperatures as high as the mid-40s, though, the flakes melt upon impact. Temperatures must be 32 degrees or lower in the clouds where snowflakes form, but because flakes can fall more than 1,000 feet without melting, they can reach the ground with surface temperatures well above freezing. One of the warmest snowfalls occurred in the 1970s in Jacksonville, Florida, when flakes were reported with a temperature of 53. The air was extremely dry, and evaporative cooling from a burst of rain chilled the air enough to produce brief snow and sleet.