10pm Friday...

A bit of a schedule change which means I'm working a Friday night (rare). What a beautiful first four days of December! Solid sunshine for most today; check out the upper 50s and lower 60s along the coastline.

Todays Observed Highs OrWa 2017.png

Low 50s again in Portland; this has to be one of the warmest east wind episodes I've ever seen in December. Typically we stay in the 40s, or colder. An approaching low pressure area is tightening the pressure gradient across the Cascades as a cool area of high pressure sits in the Columbia Basin. It's been running around 8 to 10 millibars this evening.

SurfaceHighSaturday7am.PNG

That tight pressure gradient leads to strong wind in the "outflow" area of the Columbia River Gorge. Gusty east wind from Cascade Locks all the way into East Portland. Don't expect the wind to drop off until Saturday night as a weak cold front passes by; it's going to be a windy Saturday out there. Peak gusts have been in the 40-50 mph range around the mouth of the Gorge (Troutdale/Camas/Gresham) and 60-80 mph in the western Gorge itself. I don't see a long period of strong wind NEXT week, it'll likely come and go. By the way, Vista House wind sensor is working fine, but data isn't making it all the way to NOAA yet. That should fix itself next week. A peak gust of 80 mph occurred late this afternoon up there.

Let's look ahead...

THE BIG PICTURE

  1. In general, benign weather will be the rule for the next 1-2 weeks.
  2. I don't see a weather setup that would bring lowland snow/ice west of the Cascades in the next 10+ days. That takes us through mid December. There won't be an "early winter" this year. By that I mean some years we get a cold spell and/or lowland snow in late November or the first half of December. Not the case this year...hmmm. Surprising, but not unprecedented in a La Niña winter.
  3. There's no sign of a stormy weather pattern through the next 10 days either. Most weather systems passing by appear to be weak.

So what's going on? It all boils down to the fact that upper-level heights will remain above normal over the eastern Pacific and western USA much of the time over the next 10 days. Any significant change is more than 10 days away. Models are in pretty good agreement about this. Take a look at the ECMWF ensemble average 500mb height map for North America for tomorrow evening; a weak upper-level wave is pushing through the strong ridge over us

ecm_saturdaynight.png

Notice the ridging is back by Monday. Just some light showers tomorrow evening through Sunday morning.

ecm_Mondaynight.png

Other than another stronger upper-level trough with cooler air passes through about next Thursday, followed by more ridging. This is one week from today (Friday the 11th)

ecm_friday11th.png

We don't get all that much rain out of these weak systems. 7 day precipitation forecast

ECMWF Precipitation Accumulation.png

The ridging flattens a bit, but notice heights are still above average (warm colors) by Tuesday the 15th. We're halfway through December at this point.

ecm_tuesday_15th.png

Ah, but then both ECMWF and GEM models are trying to push the ridge west about two weeks from now. A cooler/wetter pattern as we head toward Christmas Week. We'll see...

ecm_friday18th.png

One tool we use is the "850mb ensemble chart". Each line represents one of the 51 ensemble members, showing temperature in Celsius around 4,000' or so. To get snow down to sea level we generally need it below -6. Notice almost no lines go down that low THROUGH THE NEXT TWO WEEKS!

tseries_850t_000-360_Portland.png

Confirmation of that comes in the 24 hour snowfall forecast for each of those 51 ensemble members for the middle of the north Willamette Valley. It's rare December-February to see so few members producing at least some snow at some point in the two week forecast.

ecmwf-ensemble-KUAO-indiv_snow_24-7083200.png

To summarize: weather is unlikely to significantly alter your life or plans during the next 10+ days.

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