Christmas vacation so far has given us a mix of weather; from warm/mild rains to cool easterly wind. Some fog and freezing fog in spots too. In the central/eastern Gorge, you experienced the much desired “White Christmas”. 1-6″ fell from Cascade Locks to The Dalles and down into north-central Oregon. Now we’ve seen a few dry days. Portland is running near to a little below normal for rain this month. A good chunk of the region has been drier than average over the last two months; somewhat unexpected in a La Niña winter.
Most of the USA has been warmer than average this month; including the Pacific Northwest. This is our 3rd consecutive warm December.
We are approaching the “halfway point” of the Pacific Northwest storm season. That’s November-February. It’s been a disappointment so far if you’re looking for lots of active weather from this “La Niña” winter. No lowland snow, no significant windstorms, flooding, tornadoes etc… We are in the coldest time of the year (by the averages) right now. It’s always interesting to note the western USA is coolest when you would think it would be; lowest sun angle and shortest days. That’s right now. Yet the coldest of winter is more like February 1st once you get into the upper Midwest and Great Lakes regions. That’s due to the continuing cold Canadian airmasses moving south and thick snow cover reflecting much of that increasing solar insolation.
It appears weather action will be picking up again over the next week; these 12 Days of Christmas will be turning quite wet! A mid-winter Pacific jet stream will be ushering a series of wet weather systems into the PACNW starting tomorrow. We still have a little cool air stuck in the Gorge. The layer of cold air isn’t very thick and easterly gradient through the Gorge is weak. This may be just enough to bring very light snow (less than Christmas) tonight through midday tomorrow. A real “marginal” event though.
I see at least 6 separate cold/occluded fronts coming through the region tomorrow through Wednesday the 6th. You can see 4-5 of them moving quickly west to east in this loop of sea level pressure and precipitation type. That’s now through next Monday.
In general we seem to be headed toward slightly colder systems after Sunday as upper-level heights lower next week. You see the cool/lower height anomaly max out the middle of next week, before the ECMWF ensemble average pushes heights up again about two weeks from now.
At this point I don’t see any especially strong storms, although models have been waffling around each run with exact low placement and precipitation intensity. It’s quite the message here…no significant gaps in the 24 hour precipitation from any of the ECMWF ensembles
I see quite an increase in mountain snowpack the first week of January. The ECMWF model thinks 20-40″ is likely on Mt. Hood over the next week. Since snowpack is running a bit below average this is good news!
With almost constant onshore flow it’ll be tough to get snow down to sea level over the next 10+ days. Notice almost no members of the ECMWF ensembles produce significant snow over Portland the next two weeks.
That’s not to say we couldn’t have something happen like what Puget Sound saw last week. A low pressure area and dynamic cold front brought heavy post-frontal precipitation overhead for a few hours, dropping sticking snow all the way to sea level. It didn’t last long, and it warmed up in the hours following, but something quick/crazy like this could show up in the models just a few days ahead of time.
To wrap it up, my main points…
- There’s NO sign of a widespread lowland snow/ice event in the next 10+ days…January begins mild
- It’s also unlikely we’ll see an “arctic blast” in the first 15 days of January. That refers to a setup with cold arctic air drops south on north or east wind, keeping high temps in the 20s west of the Cascades and lows down in single digits or teens. I don’t see that in the cards.
- Expect rain almost every day during the next week; some days will be wetter than others, but I can’t find a totally dry day.
- Keep a close eye on the forecast during this time; a wind storm or river flooding could show up in the forecast maps just 3-4 days ahead of time.
Chief Meteorologist Mark Nelsen