Dear Tom,
How long does it take a snowflake to float down to Earth?
Ron Milnarik, Chicago
Dear Ron,
Snow expert and Colorado assistant state climatologist Nolan Doesken states the vast majority of snowflakes fall at speeds between 1 to 6 feet per second. A snowflake’s surface area and its mass are the most important factors in determining the rate of fall. Large flakes act like parachutes and slow down due to increased air resistance, while smaller snow pellets known as “graupel” fall at a much faster rate. In a typical winter storm, snowflakes begin their descent from a cloud layer about ten thousand feet above the ground. Assuming an average fall speed of 3.5 feet per second, a snowflake would take more than 45 minutes to reach Earth.
Chicago NWS forecaster Jim Kaplan, notes that when local Doppler radar depicts heavy snow returns at a radar beam level of about 3000 feet, 10 to 15 minutes elapse before heavy snow is actually observed in the local area.
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Tom Skilling is chief meteorologist at WGN-TV. His weather forecasts can be seen Monday through Friday on WGN News at noon and 9 p.m.
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