Friday, May 14, 2021

Here's why wind makes it feel so much colder

by Randy Mann
| February 15, 2021 1:06 AM

Last Friday was our coldest day of the winter season. The high temperature at Cliff’s station was a very cold 20 degrees after a low of 7 degrees. Winds were also gusty, resulting in wind chill temperatures down to near minus 10 degrees in some areas.

The heavy snowfalls over the past week have been all around North Idaho, but we remained mostly dry. According to Cliff’s records, this is one of the most snowless mid-winter periods in history.

Seattle and Portland have been reporting snow. To the east, blizzard conditions have been seen across the central portions of the country along with bitterly cold temperatures.

Places in North Dakota and Minnesota near the Canadian border reported low temperatures near minus 30 degrees Fahrenheit with wind chills around minus 50 degrees.

Snow has also been falling down in the Gulf Coastal states and Texas. Parts of the Lone Star State have seen more snow in 2021 than North Idaho.

Icy weather has been reported down into Arkansas, Louisiana and Mississippi with more hazardous wintry weather expected this week. One of our clients said that it’s an “absolute mess” with ice, traffic accidents and power outages. Over 50 percent of the country is expected to be covered with snow from these massive storms.

The big winter pattern missed North Idaho this season, but made a direct hit over much of Europe. Many areas, especially in the northern regions, were hit hard with many days of record snow and ice, sub-zero temperatures and very strong winds resulting in dangerously low wind chill temperatures.

The German weather service said that February of 2021 was the coldest February since 2012.

The big chill in the U.S. has been the result of the infamous Polar Vortex that finally moved over North America. As of last weekend, it finally looks like we’ll be getting some snowfall today and into early Tuesday.

There is another system late in the week that has the potential to produce more snow, but the air mass will be warmer, so there’s a chance that we could see rain mixing in once again.

Despite the recent lack of snow, Cliff and I still think that February will likely be our snowiest month of the season. The long-range computers are showing more storms from the Pacific Ocean that will move through the Pacific Northwest, including North Idaho, later this month.

This time around, the direction of these systems is expected to come from a cooler northwesterly direction, which increases the chances for snow in the lower elevations. However, Mother Nature still has the final word and we’ve already seen many instances of rain rather than snow.

During the winter season, we often hear about the “wind chill factor.” This is a reading that represents what the temperature “feels like” when wind is blowing on exposed skin. As the wind blows on or over the skin’s surface, moisture evaporates that leads to a cooling effect.

There are many formulas to calculate the wind chill temperature as weather services in different countries use their own standards. The first wind chill table was originally developed by two scientists working in Antarctica, Paul Allman Siple and Charles F. Passell. The National Weather Service adopted their table in the 1970s.

In November 2001, a revised wind chill index was developed and implemented in the United States, Canada and the United Kingdom. Each country has some slight variations in the wind chill formula.

According to the National Weather Service, the wind chill is calculated with wind speed at a height of 5 feet, which is the average height of an adult human face. The wind chill formula incorporates the heat transfer theory based on heat loss from the body to its surroundings when the person is facing the wind and walking at a speed of 3.1 mph. The wind chill temperatures only apply for readings at or below 50 degrees Fahrenheit.

For example, according to the wind chill chart, which is available on many websites, a temperature of zero degrees Fahrenheit with a 15 mph wind results in a wind chill temperature of minus 19 degrees. At this temperature, frostbite can occur within 30 minutes.

If the winds were to increase to over 50 mph, a zero-degree temperature would result in a wind chill reading of minus 32 degrees. In these conditions, frostbite would likely occur within 10 minutes.

In extreme cases, like the ones from the recent Arctic outbreak in the northern U.S., an air temperature of minus 20 degrees Fahrenheit combined with winds of 35 mph would have a wind chill reading of minus 55 degrees. According to the chart, frostbite would likely occur within five minutes.

If you would like to calculate the wind chill, here’s the formula. Wind Chill = 35.74 + 0.6215T – 35.75(V^0.16) + 0.4275T(V^0.16). The letter “T” is the temperature in Fahrenheit and the letter “V” is the wind speed. The “^” symbol is the power or exponent.