White Thanksgiving?

So far this autumn has been fairly mild and wet.  Except for a few days, we've consistently reached the 40s during the day, and except for a few cold days at the end of October, we haven't been very cold at night either.  In the figure below, the blue bars are the daily high (top of the bar) and low (bottom of the bar) temperatures.  The shading shows above (red), normal (brown) and below normal (blue) temperatures.  You can see that most of the blue bars are in the brown or red area, with only a few bars in the blue.  

But we all know this mild pattern will change, eventually.  The computer forecast models are now indicating that this change could take place next week, just in time for Thanksgiving.

For this week, we'll still have some weak rainy fronts moving through the region.  But temperatures will be ticking down a degree or two each day.  

By the end of the week, high pressure builds into the area from the west.  This will bring a short dry spell to the Inland NW, probably Thursday to Saturday.  But at this time of year, high pressure doesn't guarantee warm weather.  Fog and low clouds often form in these patterns and they can be tough to burn off during the days of low sun angle.

But then next week, the pattern makes a noticeable change.  High pressure in the Gulf of Alaska and cold low pressure over the Pacific NW is a good pattern for snow.

Here's the temperature anomaly pattern for Thanksgiving.  Pretty easy to see that the holiday will be cold in the West and mild in the East.

The confidence of a colder pattern is increasing.  Here are the clusters of extended forecasts.  You can see that cluster 1 and cluster 2 are forecasting the cold temperatures over the Northwest.  Those two clusters make up 67% of all of the forecasts.  Meanwhile only 12% of the forecasts are calling for warm and dry weather.

The Climate Prediction Center is seeing the same thing.

It's too early to talk about timing or snowfall amounts.  I'll update this blog as we get closer to next week.  Suffice to say, there's a good chance of seeing some snow next week.  And temperatures are cold enough that it will probably stick around for at least a few days.