We’re right on track for snowfall
January is normally the snowiest month of the season. So far we’re right on track, with storm after storm bringing in new snow, now totaling more than 41 inches for this winter. We’re also supposed to be experiencing the coldest temperatures of the season. Though we have recently taken a dip into some arctic air, we’ve also experienced highs in the 40s to near 50 on a few occasions during the last couple of weeks, which is 5 to 15 degrees above normal.
One of the reasons we haven’t had more snow on the ground in recent weeks has to do with the weather systems that have been producing the snows. Although it may sound counterintuitive, several of the last snow events have been produced by “warm fronts,” which is just a term meaning the advancement of warmer (not necessarily “warm”) air. When cold air is already in place, the warm air advances and also rides up the colder air. Assuming there is enough moisture present, the warmer air rises and cools, the moisture condenses into clouds, and eventually precipitates as snow. This happens just ahead of the advancing warm front.
What has been happening during the last couple of events, is that behind the warm front (called the warm sector), strong southerly winds have brought in very mild temperatures that eat away at the snow just after it has fallen. My poor children have been disappointed more than once as they watched snow falling in anticipation of using their new snowboards. Unfortunately, subsequent 40 degree temperatures and 40 mph winds didn’t provide the best environment for those endeavors.
Though the following scenario hasn’t quite materialized this winter, sometimes the warm front is elevated. What this means is that the advancing warm air is coming in above the surface, say 3,000 feet for example (above the approximate 2,300-foot elevation of Coeur d’Alene). When this happens, sleet, freezing rain and snow can occur at the onset of the precipitation, until the warm air mixes down to the ground and changes everything to rain.
What usually follows after a period of being the “warm sector” of a storm, is the passage of a cold front. A cold front is just the leading edge of colder (though not necessarily “cold”) air. When the cold front advances, it acts as a wedge lifting the warm air ahead of it. Again, with sufficient moisture, the rising air can lead to more precipitation. Though both warm and cold fronts can lead to precipitation in the winter time, most of our biggest snow producers are caused by low pressure systems (both at the surface and in the upper levels of the atmosphere) that lift out of southwest Oregon and pass just to our south. In this scenario, we get the snow ahead of (north) of the warm front, but never enter the warm sector of the storm. The low pressure center passes to our south and east, we remain in the cold air and the snow wraps around the low pressure in counter clockwise fashion, giving us an extended period of wintry weather that can add up to high snow totals.
Speaking of heavy January snows, some notable storms of years past include the New Year’s Day storm of 2004 which blanketed the area with 8 to 15 inches, the most ever for Jan. 1. January 1982 was also a snowy one, with a two-day blizzard during the first week of the month bringing a record 16.6 inches of snow to Coeur d’Alene and 22 inches to Hayden. More snow fell on Jan. 23 of that year, adding another 11 inches in Coeur d’Alene and 16 inches in Hayden.