Ridging over the Pacific Northwest on Wednesday along with a strong low in the Gulf of Alaska are driving mostly sunny and seasonably warm conditions in the Portland area. Meanwhile to the north, a Pineapple Express has been aiming at Vancouver Island, producing up to 200 mm (8 inches) of rain. This Pineapple Express is the boundary between warm weather to the southeast and cooler weather to the northwest.
Warm temperatures are forecast in the Portland metro area through Saturday as ridging continues. Friday into Saturday is likely to bring increased cloud cover, however, with the first in our next series of storms approaches from the southwest.
This kicks off several days with a chance of rain starting as early as Saturday night. Upper level troughing is forecast to dominate the pattern over the Northwest, swinging in additional storms off the Pacific.
Deep troughing over the Northwest will favor northwesterly flow aloft, bringing in cooler daytime temperatures. Ensemble models indicate a strong signal for rain west of the Cascades Sunday into Monday and again on Wednesday.
Modeling shows wet weather continuing beyond that but differences in timing of the storms on individual ensemble members makes it hard to predict when the rain will actually fall. It may be that our generally wet weather continues, but it may also be that the model just trends toward climatology (or average conditions), which for forested parts of the Pacific Northwest does include a bit of rain.
Cooling temperatures aloft may bring highs as low as 9-12°C (48-54°F) to Portland sometime next week but cloud cover should help to keep lows near to above 5°C (41°F) which is just a little below average for this time of year. Places like the Tri-Cities in the arid Columbia Basin will likely see warmer overnight lows than they have seen this week, again owing to additional cloud cover.
A few storms so far this season have already brought snow to the tops of the volcanoes and on some of the higher passes in the Cascades and Okanogan region. We’re still a ways out for significant confidence but the cooler temperatures coming in as part of the troughing pattern may be enough for the first glimpse of snow down to the major Cascade mountain passes.
The European model, displayed above, gives widespread freezing levels in the 900-1200 meter (3000-4000 feet) range throughout Washington and Oregon on Wednesday night. This may be enough for some snow down to Snoqualmie Pass east of Seattle which brings Interstate 90 to a summit of 919 meters (3015 feet).
This actually represents a small moderation in the models over the past two days. Earlier runs had produced somewhat cooler temperatures but what they’ve shown today is still enough for some of the coolest daytime temperatures seen west of the Cascades so far this season.
The incoming rain and snow will help to mitigate the drought currently being experienced in the Pacific Northwest but isn’t likely to be enough to bring a full rebound. Seattle Public Utilities continues to ask customers to voluntarily reduce water consumption while the Portland Water Bureau is supplementing their water supply using wells due to low levels at the city’s Bull Run reservoirs.
You can subscribe to Ingalls Weather via email below this article (on mobile) or on the top right of the page (on desktop). This service only emails new articles directly to subscribers and does not send spam.
