Nasty Wind Chills

The image to the left shows how cold the temperatures were at 11:00 AM today.

This morning wind chills were in the 10s and 20s below zero with a Wind Chill Advisory for some counties. "Why are some counties in Iowa included in the advisory but others were left out?" was a common question I was asked this morning. Well there is a method behind the "madness". By definition, WIND CHILL ADVISORY is issued for wind chills of 20 degrees below zero (F) or colder for a sustained period of time. Winds are expected to be at least 10 mph. By the way the threshold values will be "warmer" in more southern states. The next level of alerting the public is when the National Weather Service would issue a WIND CHILL WARNING. This is issued when wind chill values are expected to reach 35 degrees below zero or lower (upper Midwest, Northern Plains, some mountain areas) along with wind speeds above 10 mph. Other locations in the eastern or southern parts of the U.S. have a warning threshold of 25 below zero, or perhaps even "warmer."

The windchill temperature is calculated using the following formula:

Windchill (ºF) = 35.74 + 0.6215T - 35.75(V^0.16) + 0.4275T(V^0.16)

Where: T = Air Temperature (F) V = Wind Speed (mph) ^ = raised to a power (exponential)

Windchill Temperature is only defined for temperatures at or below 50 degrees F and wind speeds above 3 mph. Bright sunshine may increase the windchill temperature by 10 to 18 degrees F.

Here is a link to explain more about wind chill...including a wind chill chart and calculator