You're packing for that long-awaited, late-autumn trip into the Mule's Ear Wilderness. The ranger on the phone said to expect 35° to 40° F during the day, but the Weather Channel is now predicting 15 to 20 mph winds, with the accompanying "wind chill factor" making it feel like it's 50° F. So what temperature should you prepare for?
To answer that question, it helps to know the wind chill facts.
The wind chill factor refers to the rate your body cools, not to the temperature of the air.
When the air is dry, the wind cannot lower your skin temperature to less than the ambient air temperature. In other words, if the thermometer reads 33° F, that's as low as your skin temperature can get, no matter how hard the wind blows. That means you'll be uncomfortable if you're not dressed properly, but you won't get frostbite, even though your fingers may feel like they're about to fall off. You will cool down much faster, however, which is a setup for hypothermia.
Wind blowing over exposed, wet skin can drop your temperature to slightly less than the ambient temperature. Your body will cool even faster than when you're dry, and you may enter the frostbite danger zone.
When the mercury is at or below 32° F, exposed skin will freeze faster in the wind. For instance, exposed flesh freezes in 30 seconds if the temp is -30° F and the wind is blowing 30 mph. Just remember that when it's below freezing, limit the amount of time skin is exposed. Gloves are essential, as is a hat, and a face-covering balaclava is your best bet.
Bottom line:The effects of cold and wind can be subtle but devastating to the unprepared. Always carry a good wind shell, layer your clothing so you can easily adjust to stay comfortable and dry, and remember that the physically fit and well hydrated are less prone to cold injury.