Fresh Mountain Snow and a Very Dry December Start

November 30, 2017

10pm Thursday

Today was a gray day but only around .10″ fell in much of the metro area…a classic “soggy” but not “soaking” Pacific Northwest day.  The month ends in just two hours;  it was a slightly wetter than average November in Portland.

Mark November Rain

The first day of December (tomorrow) looks dry as we wait for a weakening cold front to move inland during the evening.  Another chance to hang your Christmas lights and stay dry.   For you skiers/snowboarders this is the plan for tomorrow and the weekend:

Snow Report2

There is only one wet day in our 7 Day Forecast this evening and that would be Saturday.  That’s because next week a new weather pattern takes hold.  It’s a pattern we never saw last winter;  a big “blocking” ridge of high pressure parked over the west coast of North America for many days, possibly well beyond a week.  For comparison, the last time we saw 7 consecutive dry days in December was 4 years ago.  Back in December 2011 we went 9 consecutive days without rain so it’s a rare event but it DOES happen.  Take a look at the upper-level map (500 millibars) for Tuesday.


You see the big ridge developing along the West Coast and a very cold trough pushing cold air down over the Great Lakes.  Next week I’m sure the national weather story will be winter arriving in the eastern half of the country.

In this pattern we’ll see surface high pressure set up east of the Cascades.  That will push a strong easterly wind through the Columbia River Gorge.  Tuesday is the beginning of that setup and it’s possible that east wind will continue for at least week!  In December an east wind is cold as the valleys cool off and stay chilly under wintertime inversions.  The Cascades will turn quite warm next week, likely well into the 40s or even 50s at the ski resorts.  But blue sky and clear/cold nights will keep snow melt to a minimum.

That upper-level ridge sticks around on ALL models through the next two weeks.  Check out the GEM (Canadian) ensemble average for Thursday the 14th:


and the ECMWF ensembles…similar setup with a cold eastern US and mild west (above the inversions):


On a side note, are you are headed out to a tree farm this weekend?  Then Sunday is your day.  It should be mainly (or all) dry.  Saturday looks like a soaker.

Mark Christmas Tree Forecast

Chief Meteorologist Mark Nelsen