A cold front is passing through the eastern side of the Portland metro area at this hour. That’s a dividing line between a mild airmass and cooler showers beginning to move onshore. It’s been raining in the Cascades today but that’ll switch to snow by 8pm even in the passes. I expect 6″ there and up to 12″ by morning up at 6,000′.
So tomorrow is your day to head up to the slopes! It warms up again Thursday and Friday.
Now on to the big question. Typically I hear a lot of this in mid-December:
“Do you see any snow in our future?”
This is the time of year if you want snow in the lowlands. Mid-December to early February is “prime-time” in our marginal snow climate. It’s tough enough to get snow here, but an extra feat to get snow before early December or after Valentine’s Day. So do we see anything ahead?
At this time there are no signals from any of our models that a cold (or cold/wet) pattern is on the way through at least the next 7-10 days
Now we can only see details maybe 5-7 days out; beyond time we look for general patterns on our models. You can find a list of those winter weather patterns on a “tab” above WINTER PATTERNS. Drew Jackson put these together about 10 years ago. He’s now in management down at Mt. Bachelor; probably still watching the weather maps closely!
We’ve been in “Pattern B” quite a bit the past few weeks; a splitting jet stream which is common during El Nino winters. Over the next two weeks I see a bunch of Pattern C (weak Pineapple Express) and D (mild westerly flow) thrown in as well. If you want lots of snow in the Cascades 2 out of 3 of these are not good. In fact the ECMWF only gives Government Camp maybe a foot of snow in the next week! Half of that would be tonight.
Now if you want to see heavier Cascade snowfall or snow/cold down into the lowlands you’re going to want to see Pattern “E” or “F”. There’s absolutely no sign of “E” in the next 8 days or so (cold Gulf of Alaska flow). And at this point I don’t see the “F” pattern, the one where a big ridge of high pressure develops offshore. This allows cold arctic air to plunge south into the Pacific Northwest on the back side of that ridge. Again, no sign of that pattern either.
Let’s take a look at the ECMWF model forecast temps/rain for Portland.
There is no long dry period in the next 10 days, but the only really wet systems pass through right now and again early next week. Check out those temps! It’s going to get mild the next 8 days. Other than Friday morning, we don’t even get close to freezing. Then you see the drop off in temps around Friday the 21st. Why the mild temps and lots of rain early/mid next week? It’s a weak version of a pineapple express as a flat upper-level ridge builds along the West Coast. It isn’t strong enough to push the rain north of us, but brings very warm air overhead. Here’s the Tuesday forecast. Strong westerly flow overhead = wet and possibly stormy.
By late next week we should cool back to normal and that can be seen in the ECMWF meteogram for the next 15 days. Between the 10-15 day period there is even a hint of a return to a cool & dry pattern like we experienced last week.
The GEM and GFS models agree with the ECMWF that some sort of upper-level ridging builds again over the Eastern Pacific, relatively close to the West Coast. See all three forecasts for Christmas Day
The weather patterns we have experienced these 6 weeks since Halloween have sure screamed El Nino to me. Splitting, ridging, and a real lack of lower Cascade snow or storminess along the Pacific Northwest coastline…but more on that in a future post.
Chief Meteorologist Mark Nelsen