Tomorrow’s forecast is a tough one for the Portland Metro Area. So let’s focus on what we already know.
- The coastline should be REALLY warm, by that I mean well into the 60s in some spots. Same thing in the Coast Range and Cascades. Even the Cascade foothills will be warm; basically any spot above 1,500′ should be springlike. Today there were some 60 degree temps in the Cascades…more of the same tomorrow.
- Most areas along the I-5 corridor from Longview to Eugene will see another cloudy, cool, and foggy day. High temps will struggle to get into the lower 40s.
- Part or all of the Portland Metro area will clear out as a drier east wind pours out of the Columbia River Gorge. Exactly which parts get the sun are a big challenge
Strong high pressure if firmly in control of our weather along the West Coast right now. Temperatures have surged everywhere above about 1,500. Take a look at our tower temps on top of the West Hills this afternoon.
38 at the base of the tower and mid 60s at the top! That’s a very low inversion for one, and very sharp. You can see the view this afternoon up in the 60 degree air:
Within that cold layer (that most of us are living in right now), the moisture has condensed into cloud cover and fog. That doesn’t change through at least Saturday for most lower elevation sites.
But one significant change occurs overnight that should allow a good chunk of the metro area to break free of the clouds and fog tomorrow. A “Gap Wind” develops at the west end of the Columbia River Gorge. Pressure gradients, which were westerly today, switch to easterly overnight as high pressure builds in quickly east of the mountains. Mesoscale models show about 5 millibars easterly gradient from The Dalles to PDX by sunrise tomorrow. That amount of wind should be enough to clear at least the central/east side of the metro area out by midday, possibly enough to clear areas west of the West Hills too. Clark County is a tougher call. It’s possible areas north of the Columbia River won’t be able to shake the fog. Here’s the WRF-GFS wind forecast for 10am tomorrow morning:
You can see the swath of northeast wind exiting the Gorge south of the river and heading out towards Happy Valley and Milwaukie. That’s very common. In fact tomorrow MIGHT look just like December 26th from space. Sorry to bring back that image again, but a weaker gradient produced this:
A tough forecast! My gut feeling is that 5-6 millibars easterly gradient should be enough to clear out just about the entire metro area by late afternoon. The National Weather Service thinks the gradient will be too weak to bust us out; they have a gloomy forecast for tomorrow, like today. We’ll see how the forecast turns out. May the best man/organization win!
Further ahead…not much to talk about still with the ridge hanging on. Here are the 12z GFS and ECMWF ensemble plots showing temp at 4,000′ or so over the next 16 days:
I’ll take the -20 member of the 2nd chart please for $200!
No rain in sight, unless we get a few sprinkles next Tuesday-Wednesday with a weak upper trough passing through the ridge. Dry pattern continues at least through the weekend of the 25th/26th
Chief Meteorologist Mark Nelsen