Late November Weather Slowdown In Pacific Northwest

November 16, 2021

7pm Tuesday…

The first half of November has been very warm in the Pacific Northwest, 3rd warmest on record (first half of month) at PDX.

Now that’s partially due to a long-lived atmospheric river event late last week through Monday. That was a real doozy in Washington, not as extreme in Oregon. Huge rain totals with record flooding the past few days in SW British Columbia and NW Washington. Portland picked up just under 3″ out of the event Thursday-Friday, an excellent forecast by forecast models.

Then a strong cold front finished things off yesterday with a gusty south wind that quickly switched to northwest in the afternoon. Peak gusts were in the 25-40 mph range for most of us, the 4th time PDX has seen a gust at/higher than 40 mph this season. Lots of moderate wind, but no windstorm in the valleys yet this season. Mental reminder: The HRRR model tends to over-forecast wind gusts, it’s been too high most of the time this season. Our GRAF model has done very well.

Rain is running well ahead of average for November…just over another 1/2″ will send PDX over the typical monthly allotment. But now the weather is slowing down dramatically.


WHAT’S AHEAD?

Much calmer weather which shouldn’t affect your day to day living…

Through at least Thanksgiving Day I don’t see:

  1. A storm of any sort west of the Cascades
  2. Lowland cold and/or snow
  3. A big snowfall to jump start the ski season

In general, upper-level heights will be a bit higher than normal along/off the West Coast. That has not been the case most of the time in the past month. This chart shows 500 millibar height (around 18,000′ overhead) averaged over the next ten days…the lines. Warm colors represent highs higher (warmer) than normal

That leads to less precipitation than normal…both the GFS and ECMWF ensembles are similar (GFS here). Not DRY, but DRIER THAN AVERAGE for this time of year.

Just beyond that time (later Thanksgiving Weekend and beyond) models diverge. At this point GFS ensemble members are bringing in a wet southwesterly flow again, but ECMWF & Canadian models think ridging moves overhead for drier than normal conditions through the end of November. We will see, that’s pretty far out. Regardless, I only see two rainy periods in the next week. That’s later Thursday through Friday, then again Monday (very light). These will be relatively weak systems, not significant wind producers. I love this chart…it shows all 51 ECMWF ensemble members for the next two weeks. Each square represents a forecast 6 hour maximum gust in Portland. The lowest part of the chart shows the average of all 51 members. With just a quick glance I can see where windy periods may show up, plus any real “outliers”. That refers to numbers much higher than others.

Gusty easterly wind tomorrow through Thursday morning shows up well on all ensemble members. Most interesting is that there isn’t a single ensemble member trying for a 50 mph gust in the next 16 days! Of course that doesn’t mean we don’t have a storm coming sometime beyond the next 7 days, but in general we don’t see a stormy period ahead.


SKI AREA OPENINGS

Last week things were looking up with 10-15″ fresh snow on the ground at the ski resorts. We were just a storm or two away from at least a few runs opening up on Mt. Hood. Then 5-6″ rain fell on that snow and warm/humid weather melted all of it! Cold showers last night dropped 2-5″ snow on those resorts. It appears only a dusting is on the ground down at Mt. Bachelor west of Bend. This is not unusual for mid-November as you see, but skiers/snowboarders just remember the big starts. 2017 and last year we had some nice snow on the ground at this point.

What’s ahead?

We sure don’t want to see those higher than normal upper-level heights over the next week as I mentioned earlier in the post. That means weak systems and a bit warmer than normal. So very little accumulation at the resorts at least through next Wednesday.

BUT, things can change quickly this time of year. Stay tuned to see if we get that cooler/wetter pattern as we go through Thanksgiving Weekend.

Chief Meteorologist Mark Nelsen