Sunday, November 10, 2013

An Upcoming Pattern Change?

This past week, some (most?) folks in the Inland Northwest had their first taste of snow.  But as is typical for early November, the snow didn't last.  In fact, the weather since then has been rather mild.  A somewhat confused weather pattern has developed over the eastern Pacific, giving the Northwest US an overall ridge of high pressure. Veterans Day (Monday) should be warmer than normal.

But as we all know, this won't last either.  And it may end sooner than you think.  The atmospheric models are indicating a big change in the weather pattern.  They've been doing so for a few days now, so confidence is building that this will indeed come to pass.  The mild southwesterly flow will be replaced by a cold northwesterly flow.  

The image above shows the pressure pattern at about 18,000' above the earth's surface for Tuesday.  The wind tends to follow the solid black lines of pressure, and we like to look at where the air is coming from.  For Tuesday, the air coming into our area will be from the southwest, which is typically a source of warmer air.

Compare that image with the forecast for Saturday morning, which is below.

Do you see the difference?  The storms are now coming at us from the Northwest (i.e. Alaska).  And you can guess what that means.

The forecast for the upcoming weekend is going to be a tricky one, so you'll want to keep checking on the forecast each day.  For now, here's our expectations.  

  • The Cascade and Panhandle mountains will be favored in this pattern.  They'll likely pick up 1 to 2 feet of snow above 4000 feet.  Travel over the passes could be difficult.
  • Precipitation will start Friday night and continue Saturday with a snow level around 3500'.
  • By Saturday evening, the main area of precipitation will begin to sag south of our area, into Oregon and southern Idaho.  As it does so, cold air from Canada will push into the Inland Northwest, dropping snow levels to the valley floors.
  • Valley locations could see a couple of inches of snow by Sunday morning.

Here's the forecast high temperatures for Sunday.  That's right, I said high temperatures.

And there's a decent chance that it could be colder than this.  Some of the computer forecasts have highs 5 to 10 degrees colder than this. Plus there will a stiff wind from the northeast, making it feel even colder.

The low temperature for Sunday night (as well as Monday night) could easily drop into the teens and single digits, depending on if there is snow on the ground.  Monday's high temperatures will likely be below freezing for just about everyone.   The cold spell should be brief, with temperatures moderating by the middle of next week.

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