High Winds, Cold Nights, & Another Dry Week

December 8, 2017

6pm Friday

For such a “boring” weather pattern the details for the weather geeks have been fascinating the past 24 hours.  Consider that:

  1. Temperatures soared into the 50s on Mt. Hood today…55 at Timberline Lodge!  In fact a few spots in the western Cascade foothills were in the 60s.
  2. Meanwhile, as expected, temperatures in the lowlands have continued to drop as cool air becomes established in the valleys & Gorge under an inversion.  Today was the coldest day so far this winter at PDX.  That’s right, you need to go UP at least a thousand feet to warm up!

3.  That’s due to the end of the mild downsloping wind off the Cascades.  Now all that air moving from east to west across the state has to squeeze through a very shallow layer under the inversion through the Gorge.  Check out the metro peak wind gusts…all areas west/south/north mainly calm…

4. Yet within the Gorge and far east metro the wind has continued to pick up.  The wind at Corbett has gusted above 70 mph every 10 minute period since 3pm…that’s unusually strong even for them.  The raging wind continues through the weekend.

I notice temperatures in the mountains will probably warm a few more degrees by Sunday as 850mb temps rise into the mid teens.  The strongest wind event I remember in the Gorge was when 850mb temps got up around +18 in January 2009.  That really squeezes the air down and speeds it up.  By the way, I drove by the Vista House wind sensor at midday.  It looks beat up, bent down and back a bit, which accounts for the “low” wind speed there the past two days.  Combine the wind and cooling airmass coming through the Gorge and it feels like mid-winter out there.  Here are the 6pm windchill values.

Ice has also begun to form on Gorge waterfalls.  It will be a great weekend to check out the wind, waves, and icy waterfalls in the Gorge.  I found this just on the road to Vista House at midday:

And the river will look like this pic from Kirk Mattila.

With such a dry airmass and our long winter nights, temperatures in calm areas have been plummeting.  Check out the mid 20s in many areas this morning.  Expect more of the same the next few days:

 

This general pattern continues through about Wednesday next week.  That will be our 10th dry day in Portland.  However it appears things will be changing after that time.  The most reliable model and its ensembles show onshore flow (and the end of the cold east wind) Thursday/Friday next week as the strong upper-level ridge flattens and systems go by to our north.  This happens to be the one pattern that can minimize or eliminate the threat for snow/freezing rain as we go back to milder weather.  We’ll see how it pans out, but we might be back to gray and drippy conditions later next Thursday or more likely Friday west of the Cascades.

Beyond that, models are in disagreement whether we go into a cooler/showery pattern with the big ridge moving farther west offshore, or stay in milder westerly flow with weak ridging.  The net effect doesn’t appear to be a return into a soaking wet November-like pattern.  Note the ensemble average precipitation from the ECMWF is only 1″ in the week leading up to Christmas.

So enjoy at least another 5 days of dry weather with sunshine, then most likely we’ll turn at least a little wet and much grayer late next week.

Chief Meteorologist Mark Nelsen