Dear Tom,
Last Sunday morning, the temperature was in the mid 40s, and a wind chill was reported. Later in the day, when the temperature had climbed to the mid 50s, no wind chill was given. Is there an upper temperature limit to report wind chill?
Richard Dreger, Batavia
Dear Richard,
The high temperature that triggers the cut-off to report wind chill varies by data source. On automated airport hourly observations, it’s 35(degrees). On the National Weather Service wind chill chart, updated in 2001, it’s 40(degrees)–probably the best value since wind chills have noticeably less affect on exposed skin above that. At 40(degrees), a 20 m.p.h. wind creates a wind chill of 30(degrees); increase the wind to 40 m.p.h. and the wind chill drops only to 27(degrees). Many wind chill calculators stop at 50(degrees). Using the wind chill formula, the wind chill actually becomes warmer than the air temperature after about 70(degrees).
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Tom Skilling is chief meteorologist at WGN-TV. His forecasts can be seen Monday through Friday on WGN-TV News at noon and 9 p.m.
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