MINNEAPOLIS - When the icy blasts of winter return to North America, those fearsome wind chill numbers won't sound quite as ominous as before.
The National Weather Service and its Canadian counterpart are switching to a tamer formula for computing wind chills, one they say will provide more accurate information.
The combination of bitter cold and biting wind that generated a wind chill index of 70 below last winter, for example, will work out to 44 below with the new formula.
The new numbers will give people who dare to venture out in such weather a more realistic guide to how they should bundle up, since they'll be based on how the wind actually feels to exposed human skin.
The old wind chill charts were based on research in Antarctica in 1945, when scientists measured how wind affected the rate at which water froze. The new research studied how wind and cold really affect people.
Randall Osczevski, an environmental physicist with the Department of National Defence in Canada, directed tests in which a dozen volunteers with temperature sensors attached to their faces were blasted in a wind tunnel.
"The new wind chill index has been clinically tested," said Mark Tew, a National Weather Service meteorologist in Silver Spring, Md., who chaired a joint U.S.-Canadian task force that developed the new formula.
One of the key differences is that instead of using the wind speed measured at 33 feet above the ground, meteorologists will now use readings taken at 5 feet. "Face height," Tew called it. The new formula also takes advantage of advances in science, technology and computers, he said.
The chart also highlights the danger of frostbite, which can occur within 15 minutes when the wind chill index is 18 below zero, Tew said. The old system simply showed graduated zones of danger.
The wind chill numbers aren't a great deal different than the old system when winds are light, 10 mph or less. They're substantially less extreme under the new system as winds increase above 20 mph.
The new formula could be a boon for businesses such as ski areas, which might not have to work so hard to overcome frigid forecasts, said Kim Jackson, a spokeswoman for Killington Resort in Vermont.
"We are constantly battling the perception of wind chill," she said. "The minute you throw that word 'below' in there, that's what scares people."
If a late week forecast shows weekend wind chills won't be extreme, more skiers may plan to hit the slopes, Jackson said. And the more accurate figures will make them dress appropriately, she added.
It's already rare for school to be canceled in cold-weather states because of wind chills. But students may enjoy more outdoor recess time, said Edward Anderson, superintendent of schools in Aitkin, in central Minnesota.
Mike Stewart, a National Weather Service meteorologist in Duluth, doesn't expect many people to change how they cope with winter just because of the new numbers. He said "it's still bad enough" whether the wind chill index is 30 below or 20 below.
"That still tells me it's awfully cold out there, and I better button up," Stewart said.