A quick guide to weather warnings

With the official start to winter less than a month away, many folks are already asking, “When are the bigger snows coming?”

Last Friday, the Inland Northwest finally received its first snowstorm of the season. At the Spokane International Airport, nearly 1.5 inches of snow was measured. Over two inches of snow fell in North Idaho.

As Pacific storms roll through our region, there will be a number of weather advisories and warnings issued by the National Weather Service in Spokane. The criteria for issuing some of the advisories or warnings can depend on the time of year and/or the elevation. During the holiday season, it’s a good idea to know what’s in store, especially if one will be driving.

For much of the Inland Northwest, the mountains refer to any elevation above 3,000 feet. This year, the National Weather Service has simplified the advisories and warnings for winter conditions.

A winter weather advisory for snow is issued when two to four inches of snow is expected in the region. The advisory is upgraded to a winter storm warning for snow and, possibly, heavy snow if the valleys are expected to exceed 4 inches in a 12-hour period. Strong winds, blowing snow and sleet would be included in a winter storm warning.

Another type of advisory is a freezing rain advisory. These are issued any time the surface becomes hazardous due to this type of precipitation. An ice storm warning is issued when the area is threatened by more than a quarter inch of ice. A blizzard warning is rare in the Inland Northwest, but is issued when visibility due to blowing snow is reduced to a quarter-mile or less and winds are 35 mph or stronger. Also, a blizzard can occur even after it has stopped snowing, especially if there are strong winds that reduce visibility.

It now looks like our major pattern change is on track. That strong ridge of high pressure is already weakening that is allowing moisture to move into the area. Much colder and snowier-than-normal conditions are still expected from next week to the end of January. The normal December snow at the airport is 15.1 inches. Coeur d’Alene’s average is 19.3 inches. The chance of a white Christmas in our region is still better than 50/50.

January, and perhaps early February, will likely be colder than normal with sub-zero readings possible in around the first two weeks of 2009. The temperature could dip to as low as minus 20 degrees or colder in parts of North Idaho, and to near minus 30 degrees in Western Montana.