Weather Blog

There's cold beyond them, thar hills

There's cold beyond them, thar hills
Some of you who are astute weather forecast model watchers might raise an eyebrow to what the latest long range models are advertising for around the first week of December.

On Monday morning, the models showed a big pool of arctic air coming down from Alberta and heading into the Intermountain West, while showing that arctic air reaching all the way west into Western Washington.

But wait! Before you go start your panicked rush to the stores, the forecasting models are forgetting one thing -- there's hills between here and there. Really big ones. Like...the Cascade and Rocky Mountains.

When a big arctic high comes out of Alberta, long range models tend to way overestimate the western intrusion of arctic air because beyond 7 days, the models run at a lower resolution for topography, meaning it doesn't quite factor in the blocking power of the Cascades and Rockies correctly.

In reality, most of that air is destined to be trapped on the eastern side of the Rockies, and what does make it over, will remain trapped on the eastern side of the Cascade Mountains.

That doesn't meant it won't be cooler here, just likely not as cold as the model currently advertises, and I suspect as the days get closer and the time frame enters the period where the models run at higher resolution, it'll correctly pick that up.

For a better shot at arctic air, the arctic high needs to come out of British Columbia, and it really helps to have some sort of storm offshore (as in, a big area of low pressure) to draw that cold air through the mountains over here.