Temperatures to drop as cold air makes it over mountains

Are you ready for the first Arctic blast of the season? Mother Nature has taken it easy on us so far this month when it comes to chilly temperatures.

Referencing Spokane numbers, November has been significantly warmer than normal. The overnight low only dipped below freezing four times during the first 18 days of the month, and 28 degrees was the coldest reading (though outlying areas in both Eastern Washington and North Idaho have probably already experienced much colder temperatures).

I still have plenty of colorful flowers in bloom in both my bark beds in the backyard, and some pots on the front porch, but I know they’re living on borrowed time. I’ve been watching the computer forecast models, which have shown a building area of high pressure up north across the Northwest Territories, just waiting to dive down, bringing with it some chilly Arctic air.

Oftentimes, we are spared the worst of the bitter cold air, with the Northern Rockies providing somewhat of a barrier. If the cold air is too shallow, it remains east of the divide, diving down instead into the central and even southern plains. But with sufficient depth of cold air, it is able to “spill over” the Rockies into Eastern Washington and North Idaho. It looks like we’ll be seeing the spillover this week, leading to temperatures in the teens and single digits, with some areas potentially seeing sub-zero conditions.

Though the initial passage of an Arctic front can bring some snow, the origin of the air mass is continental (over land), rather than marine, meaning that it is usually pretty dry. What it does, however, is set the stage of cold air in place, so that the next storm system with sufficient moisture can potentially drop more substantial snow. Depending on how warm the air is in subsequent storm systems, we also have the possibility of seeing sleet, and sometimes even freezing rain if shallow cold air does not get scoured out.

Though I hate to make longterm forecasts (the deadline for my article is early Thursday), computer models are showing a broad ridge of high pressure remaining in place as we head into the Thanksgiving holiday and shopping the day after. This would result in mainly dry weather, with the worst of the cold air having moderated to more seasonable levels. Here’s hoping the computer models have a good handle on things, and that you all have safe travel conditions during this Thanksgiving holiday weekend.