‘Arctic outbreaks’ cause cold temperatures

After three weeks of mainly wet November weather across the Coeur d’Alene area, Mother Nature finally brought some significant snows to the lower elevations to finish off the month with above average snow totals. Coeur d’Alene ended up with more than 15 inches of snow for November, with an impressive 7.4 inches of total precipitation.

With overnight lows near zero, the month also ended with the coldest temperatures of the season. These “arctic outbreaks,” though not common across the Inland Northwest, occur when strong high pressure from Canada moves south into the area, bringing in cold and dry “continental polar” air. The term continental means the air mass originated over land, while the term polar indicates its origin in the subpolar Canadian north and Alaska. The coldest temperatures are realized if significant snows precede the high pressure. Dry continental polar air usually leads to a period of clear to partly cloudy skies, and in combination with fresh snow, creates the perfect ingredients for an extremely chilly night.

One of the reasons we are spared more frequent occurrences of bitter cold air across the Inland Northwest is the presence of the Rocky Mountains. Oftentimes, the cold air flows southward just east of the Rockies, with the mountains acting as a western barrier. When the cold air is deep enough, however, it can spill over the ridge and into the Idaho Panhandle and Eastern Washington. Unfortunately, for folks in the northern plains, the flat land offers no protection from the dense cold air which comes barreling down. Strong winds often accompany the bitter cold, which can lead to dangerous wind chills and or blizzard conditions if there has been recent snowfall.

Though blizzard conditions are rare in this region, we can still feel the chilling effects of cold temperatures plus wind. A wind chill can be defined when temperatures drop below 50 degrees and winds are greater than 3 mph. The wind chill factor doesn’t really become important though until we’re dealing with subfreezing temperatures.

We use the term wind chill because it is possible for our body to feel colder than the actual air temperature. In calm air conditions, the heat that our body radiates stays close to our skin. Under very windy conditions this heat is whisked away, and the danger of frostbite increases. It should be noted that wind chill applies only to people and animals, and will not actually cause other objects to cool below the air temperature. When wind chills become particularly dangerous, usually considered a reading of minus 20 degrees or below, the National Weather Service issues a wind chill warning. At a temperature of 0 degrees with a 15 mph wind, the wind chill is minus 20 degrees. Under these conditions exposed skin can freeze in 30 minutes.

As El Niño continues to strengthen, December temperatures should lean toward the warmer side of normal. November’s wet weather should give way to drier conditions as well this month. The weak El Niño of December 2004 was the warmest December recorded in the area, with a mean average temperature of 33 degrees. With that in mind here is a look at the “normals” for this month:

“Average December snowfall for Coeur d’Alene is 19.3 inches, with an average total precipitation of 3.92 inches.

“Average high temperatures range from 39 degrees at the beginning of the month to 35 degrees at the end.

“Average lows drop from 28 degrees on Dec. 1 to 23 degrees on Dec. 31.