Sunday-Tuesday gave us quite the wake-up call; “East Wind Season” has arrived. We are in a 3 day break (through Friday), but that wind will come roaring back for a longer stay starting Saturday.
Why? It’s because upper-level high pressure is developing again just offshore, blocking weather systems from entering the Pacific Northwest. At the same time a cold airmass will be dropping down into the northern Rockies and northern Great Plains. Cold air is dense and heavy = high pressure. Here’s the surface map for 10am Friday. Light wind through the Gorge, and most of the region
But you see the cold air (blue colors) gathering to the north? That associated with much higher surface pressure up there. That cool/dry air sweeps south through Eastern Washington and just 20 hours later (Saturday AM) is bottled up east of the Cascades. This is a repeat of what we saw last weekend. Maybe even a touch colder, it’s occurring a week further into the cool/inversion season. Looks like maybe a 6-8 millibar gradient through the Gorge.
The 1.33 km WRF-GFS model shows the widespread gusty easterly wind across almost the entire metro area Saturday afternoon. Saturday should be a very windy day across the area. This initial wind Saturday will be a mix of “downslope” and “gap” wind. Expect gusts 30-45 over the hills and east metro, up to 30 mph anywhere else in the metro area.
Then on Sunday you can see the typical “gap wind” look to that surface high pressure east of the Cascades. Again about 8 millibars easterly gradient across the Cascades; similar to last weekend’s forecast.
At this point the cool/cold air has settled in east of the Cascades and temperatures begin warming overhead. The high pressure has become a “closed high” in the Columbia Basin. You can usually assume the wind will be concentrated more closely around the west end of the Gorge and east metro area at this point. Of course hilltops too.
By Sunday/Monday we should be seeing gusts 60-70 mph in the western Gorge again with gusts 40-50 right around Troutdale/Camas/Washougal metro areas. At the same time wind backs off for the rest of us. It should look about like this down at Rooster Rock State Park
Temperatures will be dropping Sunday-Tuesday in the Gorge & metro area with that chilly easterly flow.
Highs will drop into the upper 40s by Tuesday (mid 40s near the Gorge) here in Portland and into the mid-upper 30s in the Gorge. It’ll be a chilly wind once again!
This setup continues through at least Tuesday, possibly Wednesday/Thursday too, depending on which model you prefer. We’ll have to be on the lookout for freezing rain in the central/eastern Gorge again next Wednesday/Thursday if the ECMWF & GEM are correct bringing in precipitation at that time.
By the way, models are showing a wetter pattern for at least a few days beginning Wednesday. Yet they still look “splitty” and weak. I don’t think we’re entering a big pattern change, but at least we’re headed toward some more normal wet weather for the long Thanksgiving Weekend.
Chief Meteorologist Mark Nelsen