Widespread freezing rain/ice storm likely heading into Christmas weekend

The timing couldn’t be any worse could it? I know LOTS of you have plans for either road or air travel late this week and into the holiday weekend. Well, it appears the biggest winter storm we’ve seen since the Valentine’s weekend snow/ice storm in 2021 is headed our way. This includes not only the Portland metro area, but likely even (briefly) reaching out to parts of the coastline and down into the entire Willamette Valley. And the Gorge...well, most likely not much will be moving there Friday through Christmas Day. It’s still 3-4 days out, but our models are in excellent agreement on timing and impacts. First a summary for the TL:DR folks

Summary & Timeline

• Cold arctic air pours south into the northern half of Oregon Wednesday night and Thursday. It’ll be relatively shallow cold air west of the Cascades, less than 2,000′ deep; much deeper east of the Cascades in northern Oregon.
• Thursday will be bitterly cold in the Portland metro area. Gusty east wind and highs only 25-30! We haven’t seen that in two years. Wind chill down in the single digits and teens all day. Gusts could top 40 mph. Yet we remain dry through most of the daylight hours. At some point late Thursday (sometime between early afternoon and midnight), snow or ice pellets begins falling. Exact precip-type is TBD, but my gut feeling is that we’ll only see a brief period of snow if we get it.
• Between Thursday evening/night and Sunday, several waves of rain will pass overhead. Snow levels jump to 7,000′ and above through the weekend! But the stubborn thin layer of cold air persists in the Willamette Valley, metro area, and Gorge. These events almost always proceed in the same order. As cold air thins in the valley & coast first, freezing rain (liquid rain that freezes on contact) changes to rain as temps rise above 32 degrees. At some point west/south metro go above freezing, then east metro rises above freezing. This process should take about 2 days in this pattern. Then, finally, the Columbia River Gorge starts a thaw. That final step likely won’t occur until at least Christmas Day (Sunday), or even Monday! This setup is “perfect” for a major ice storm, if not in the valley or metro area, for sure in east metro and into the Gorge.
• So...expect widespread freezing rain Thursday night and Friday, then more freezing rain Friday night and Saturday in much of the metro/Gorge (only). Then by Sunday hopefully just about all areas west of the Cascades will be above freezing and Christmas can proceed (with lots of leftover power outages). The Columbia River Gorge will be locked up snow, then ice from Friday through Sunday. Melting may not occur until Monday there. Plan on staying in place out there. Although possibly Friday could be mainly snow east of Multnomah Falls = better.
• Assume much of the I-5 corridor could “shut down” driving-wise Friday, for one day. Then there’s a decent chance at least half the metro area is still frozen through Saturday. Maybe roads are much better west/south metro...maybe. Worst-case scenario is that it’ll be hard to move in much of the Portland metro area all of Friday and Saturday with lots of freezing rain and power outages. A memorable Christmas ice storm. Best case is that most of the I-5 corridor is in good shape by midday Saturday and ice storm conditions are only confined to east metro areas near the Gorge. That’s best case.
• Flying Friday or Saturday? Well, be nice to those folks working at the airport because their job is now much tougher. That could be a mess

IF YOU HAVE A CHOICE, TRAVEL ON THURSDAY. It should be dry throughout the region

Details

It’s great to see models in really good agreement 4-5 days ahead of time. By Saturday evening it was becoming obvious that something big is on the way late this week. The upper-level pattern remains the same with a cold upper trough just to our north.

It sends a little upper-level system (shortwave trough) through the Northwest late tomorrow and Wednesday morning

Then by Thursday evening, a warm southwesterly flow is developing in the upper atmosphere. Snow levels are going through the roof as a system approaches. This warm/wet pattern will continue through much of next week too. Best skiing is in the next 48 hours!

Here’s the problem, at the surface that Wednesday system moves by and allows cold arctic air to pour southward. By 7am Thursday, this model (likely a little too cold), shows temperatures around 2,500′ at ZERO over Hood River and The Dalles. We haven’t seen air that cold in a few years, that’s colder than with the February 2021 event. Now I mention it’s “too cold”, but Thursday has looked the same on maps/models for a couple days.

That cold air will pour through the Columbia Gorge Wednesday night and Thursday, blasting us with strong wind, temperatures in the 20s, and bitterly cold windchill. It also filters onto the north coastline and south to Eugene. Notice the strong easterly wind 50-60 mph just a couple thousand feet above the surface on the WRF-GFS model...for Thursday

Most models have precipitation arriving 4pm-10pm Thursday. That’s just a first guess. So the first snow/ice pellets/freezing rain MAY impact the Thursday evening commute. If it starts as snow, it can’t last long because forecast soundings imply warming overhead happens quickly. This GEM sounding from 7pm Thursday shows the warmer layer arriving overhead around 3,000-5,000′. “Warm” means above freezing in this case. I don’t see any model producing more than 1/2″ snow before the changeover.

One big question is how much precipitation do we get Thursday night through Saturday? Models are all over the place so we’ll have to wait and see. Generally anything over 1/4″ ice glazing in the Willamette Valley and much of metro starts to cause power outages. Once it hits 1/2″, then things are getting real with lots of limbs down and outages. Here’s the Euro’s guess. This is by midday Saturday. Icy. Then of course there would be more ice later Saturday and Sunday IN the Gorge where temps likely remain below freezing.

What Could Change the Forecast?

The number one element that could throw things off is if models are handling the arctic airmass to our north badly. If Portland is only 35 on Thursday/Friday instead of 28, that’s a very different story and much of the Willamette Valley and coastline could avoid freezing rain. We’d have a shorter episode of freezing in the metro area too, maybe Friday only. For now I’m not seeing that, especially since the dependable models have handled the southward progression of arctic air today quite well. It has made it into north-central Oregon and west of the Cascades down to Seattle. It will actually be pushed back out of those areas tomorrow as southerly wind takes over for a day, but then it’ll be pulled back south Wednesday as mentioned earlier.

Lots more details to come this week. I’ll be at work every day through Friday and we have all our morning/evening shows on TV. Stay tuned!

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