Back in August, I reported that the National Weather Service had updated its wind chill index. The new, more accurate wind chill was designed in partnership with the Meteorological Service of Canada. Unlike the old one, which was based on experiments done with water-filled plastic bags, the updated wind chill is based on clinical trials.

Because of the wind chill revision, the Weather Service has updated its criteria for wind chill alerts. If wind chills are expected to drop to -10, they'll issue a Wind Chill Advisory. If wind chills of -25 or below wind chills are expected, a Wind Chill Warning goes out, which means frostbite can occur on exposed skin in 15 minutes or less. Wind chills that low are very rare around here - for example, you'd need a temperature of zero with a 25-mph wind.

You can get a copy of the new wind chill chart by going to our Franklin Facts web site. And for those of you mathematically inclined, you'll even get a look at the formula used to compute the wind chill values - but you may want to dust off an algebra textbook first.