Mild & Dry November; A Big Change Possible For Thanksgiving Week

November 18, 2019

7pm Monday…

What a November it has been, plenty of sunshine and warm temperatures at times.  The entire western USA has been VERY dry since late October; most areas west of the Rockies are under 50% of average.


Of course temperatures have been mild/warm too.


The only part of the Pacific Northwest a bit cooler than average is the Columbia Basin.  This November is tracking similar to one year ago.

Mark November Rain

Although last year the mild/dryish conditions continued through the end of January!  We’ll hope that’s not the case again this year.

A weak weather system is moving through tonight, we’ll probably end up with a quarter inch of rain or so.  A few inches snow fall up at the ski resorts too.  But this is a one-shot deal.  It’s back to dry tomorrow midday all the way through Saturday.  Expect a gusty east wind to return Wednesday PM and Thursday as well, but nothing crazy strong.

To summarize:  Not much happening weather-wise through at least Saturday.

Why so dry & mild?  Again we have persistent upper-level ridging in the atmosphere.  It’s either shredding storms apart as they move toward the West Coast, or shunting them to the north.  The result is mild temps and not much rain.  Here’s Thursday’s forecast from the ECMWF, showing the warm colors (above normal heights) again over our area.


Same thing Saturday, although the ridging is flattening quite a bit.  Something appears to be changing


The upper-level ridging wants to push westward out over the eastern Pacific.  By Monday a chilly upper-level trough has dropped over us and into the central USA.  We should see a bit more mountain snow either Sunday or Monday.  Each model and model run is a bit different since we’re talking 7 days out.


Looking ahead to Day #9 (Thanksgiving Day!), all three main models show there has been a change to cool upper-level troughing over the Pacific Northwest.  That’s quite a change!  The ECMWF ensembles (images below are all ensemble averages, not a single model run) seem to be a bit hesitant making a big change.  Notice it wants to hang onto the ridging a bit more.  Not sure what to think about that.

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What does this mean?

  1. There may be a significant change in our weather beginning Sunday.  We may actually go back to normal!
  2. That would mean snow levels down below the passes, significant mountain snow, and valley rain at times
  3. Thanksgiving skiing is a possibility in this setup.  As I mentioned, each model run is different.  Check out snow forecast graphics from the Canadian, Euro, & American models.  They show total snow now through Thanksgiving Day.  All show at least a foot of snow, some much more.  Ignore the little bit of snow over the metro area.  That’s a graphical contouring issue.

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I did have a brief panic last night when the ECMWF showed a snowstorm over the Portland Metro area the day before Thanksgiving.  That’s another reason to stick to “ensemble forecasting”.  It was one of only a handful of the 51 members bringing snow showers into the lowlands.  It is gone in today’s run.  But it IS time to think about winter storms/snow/ice/wind/flooding. These three months from mid-November to mid-February are “action time” west of the Cascades.

Winter Months Explainer 2017

Here’s your Mt. Hood ski area forecast.  Expect some snow tomorrow, it’ll melt, but then a few more inches around Sunday/Monday.

7 Day Forecast GOVT CAMP

Chief Meteorologist Mark Nelsen