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There’s nothing simple about the formula used to measure the wind chill temperature, unless you’re quick with decimal exponents.

But there is an underlying concept that’s pretty easy to understand. When the wind chill figure goes south of 17 degrees below zero, frostbite can occur on exposed skin in 15 minutes or less.

And now we’ve got wind chill factors well below that.

Wind chill, while complex to compute, helps measure the rate of heat loss on the human body from the combined effect of low temperature and wind, according to the National Weather Service website.

The current two-day storm that began pummeling Western New York on Monday has had no trouble registering nasty wind chill temperatures, expected to reach 30 degrees below zero across the Niagara Frontier and 40 degrees below in the Southern Tier.

How did meteorologists come up with that 40 degrees below zero number for the Southern Tier?

The real temperature there was expected to dip down to 10 to 12 degrees below zero Monday night.

The current wind chill chart shows that 10 degrees below zero, combined with the expected sustained winds of 30 mph, gives you a wind chill reading of 39 degrees below zero.

“That formula is designed to approximate the amount of heat loss on exposed skin,” National Weather Service meteorologist Jon Hitchcock said Monday. “The main point is to stress how quickly you can get into trouble with frostbite and hypothermia.”

Unless you’ve got an MIT degree or teach math, the actual formula to calculate the wind chill factor is complicated. It adds and subtracts four different figures; the most complicated involves multiplying 0.4275 by the temperature by the wind speed raised to the 0.16th power.

In other words, it’s time to pull out the chart, plug in the temperature and wind speed and get the wind chill.

While experts want to warn the public about the risks in such bad weather, being prepared is the key.

Hitchcock mentioned snowmobilers, who often go out in freezing temperatures, traveling 40 to 50 mph and thus create their own wind chills.

“If you put enough layers on and have proper equipment, you can be fine,” he said. “But most people don’t have that special equipment or take the time to put extra clothes and blankets in the car.”

Earlier Monday, Hitchcock said the combination of snow, high winds and low temperatures could combine to make the driving conditions so risky that “this may be a once-in-a-10-year storm.”

Clearly, weather experts don’t see such low wind chills here every year.

“I’d say we hit this cold once every four or five years on average, as far as wind chill goes,” Hitchcock said.

Wind chills date back to before World War II, when two men working in the Antarctic hung a small plastic bottle on an expedition hut roof, measuring both the wind speed and how quickly the bottle’s contents froze.

The National Weather Service began reporting those figures in the 1970s, but different indexes have been used, and many have questioned whether the wind chill temperatures are exaggerated.

The problem was that the wind chill, computed from the temperature and wind speed, was defined as the temperature your body would feel in the complete absence of any wind. But researchers later determined it was almost impossible to have no air movement. So a new formula was created in 2001, using 4 mph as the new figure for the “absence of wind.”

That resulted in a new chart which provides less severe (warmer) figures, although many skeptics still question whether the figures are exaggerated.

email: gwarner@buffnews.com