Well-advertised cold snap arrives Wednesday night; snow chance continues for lowest elevations too

Weather this weekend and today is uneventful, lots of clouds but not much rain. Tomorrow will be a wet day though with lots of snow in the Cascades, plus strong wind is likely tonight east of the Cascade crest centered along the Columbia River. Expect gusts 55-70 mph around Goldendale, Biggs, Arlington...out to Hermiston late tonight.

Then all the action shifts to “cold and possible snow” Wednesday and Thursday. First the highlights in case you have a short attention span, or sneaking in a quick weather blog read before the boss notices...

HIGHLIGHTS FOR LOWEST ELEVATIONS, GORGE, COAST

A cold airmass drops into the region Wednesday night, similar to the cold we experienced back in late January. But this time there is a lot more moisture = better chance for sticking snow in the lowlands...or at least somewhere in the lowlands

1. Snow level tomorrow and tomorrow night will remain above 1,000′. Just lots of showers, maybe a rumble of thunder or hail. Snow at times in Coast Range passes, but not too much (3-5″).
2. Wednesday, through the daytime, I do not expect a frozen/snowy city. Could be some dustings around in the morning (or not), best chance would be on hills. Daytime temperatures reach 40 with mixed or snow showers. Your life should proceed normally during the daylight hours Wednesday.
3. There’s a decent chance some area between Longview/Astoria (north end) and Eugene/Florence (south end) gets a surge of snow showers Wednesday around sunset and beyond. At that point it would be cold enough to stick anywhere. If your neighborhood is going to get more than 1/2″ of snow this week, this is the most likely time. Gut feeling is that we’ll see a huge variety of snow totals west of the Cascades. I’m thinking somewhere between a Dusting to 4″. Really! A big contrast in totals as we saw last week. We hopefully can narrow that down a bit tomorrow.
4. Wednesday night through Friday a cold east wind blows out of the Columbia River Gorge and into the western valleys. Highs only in the 30s those days plus wind = chilly! But we should be dry Thursday and Friday with abundant sunshine. That “strong-ish” late February sunshine will help a bit. Nighttime temps drop into the 15-25 degree range again as we saw in late January. I’m not worried about normal house pipes bursting from the cold since days will be well above freezing.
5. For this reason, we’re calling Wednesday a First Alert Weather Day for all locations west of the Cascades. This means weather could disrupt your plans that day. Again, most likely late in the day if it’s going to happen. Plus maybe a few morning school delays in the hills Wednesday.

Temperatures moderate Friday through Sunday and moisture returns Sunday, mainly (or all) in liquid form.

CASCADES

Models have backed off a bit on heavy snow totals. Still, 8-12″ is likely in the Cascades tomorrow and another 4-10″ Wednesday. That’s a solid 1-2 feet spread over two days. The Cascades are breezy today, but nothing unusual so far. Mt. Hood Meadows decided to close today, which is interesting since the 1st half of the day has been reasonable wind-wise. Both Timberline and Skibowl are operating normally. There WILL be a big ramp up in the Cascades this evening. Then a bit more reasonable again tomorrow and beyond. Thursday could be a wind + windchill issue day like we saw with the January cold snap. Temperatures only around 10 degrees that day. As I recall, 1 or 2 resorts closed on the coldest day. So Wednesday and Friday look best in the mountains.

WHAT I’M SEEING THIS AFTERNOON

A deep upper-level trough has begun digging down across the region. That’s a “dip” in the jet stream. Tomorrow morning one fast moving “wave” (#1) is crossing the area, pushing a cold front past us down near sea level.

Number two is over us by Thursday morning. What’s changed from last Friday is that models are digging this wave slightly offshore = more moisture gets picked up for showers on Wednesday, even into Thursday morning.

This upper level pattern is THE SETUP you want for snow in our area. Moisture plus cold modified arctic air arriving from the east. Take a look at 850mb temps on Thursday morning. Of course in Celsius. This is the ECMWF ensemble average. This matches the -9.3 degree temperature over Salem on the January 29th sounding. Cold stuff! Single digits at 5,000′ banked up against the east side of the Cascades. Now last month models did back off on the cold in the last 48 hours leading up to the event. We will see if that happens again...soon.

There it is at the surface...a weak low pressure center is forecast to hover just off the coastline Wednesday through early Thursday underneath that upper trough. East wind through the Gorge at 10pm Wednesday. Getting chilly...

As for precipitation and snow. Models have been all over the place the last 3 days. Again, because we’re in a showery pattern, location of any organized shower bands is tough for models to pinpoint. This pattern in October or April would just be a forecast of “scattered showers” and no one would care exactly where and when the showers show up. Different story when it’s 30-35 degrees!

An interesting graphic here shows the last 2.5 days of model run snow forecast totals (latest on bottom) from the GFS over Aurora/Oregon City. This is 24 hour totals. Any one box is the 24 total ending at that time.

Notice that generally it’s consistently showing at least 1-2″. Same graphic from the ECMWF model, but it goes back 4 days

Not as consistent. But remember this is only one spot. Here’s the Euro forecast for total snow Wednesday 4pm-Thursday 4pm...when it would be cold enough for widespread stickage.

This is why I think SOME AREAS will get decent snow Wednesday evening/night, but not others. GFS for the same period

Our IBM-GRAF, ending 4am Thursday. This model initializes with the ECMWF model. It’s juicier.

And finally the ol’ trusty WRF-GFS (although it wasn’t last week) says “weak sauce, still no need to bring out the snow blower”. It also says our BIG 0.2″ seasonal snow total at PDX will remain unchanged.

SUMMARY

Even though we’ve been pointing to Wednesday as a possible snow day for some of us for at least 5 days, we still don’t have a good handle on who exactly gets sleddable snow. But some of us in the lowlands should get it by Thursday morning at the latest.

It’s extremely unlikely (even if we get 2-4″ snow) that the city will shut down for a whole day. I’m only aware of that occurring once this late in the season since the PDX weather station was established in 1940. That was March 3rd, 1960. High of 29 that day. The situation this week may be similar to late February 2018. We had several snowfalls (either morning or evening) as a few B.C. sliders moved down the coastline that month. Airmass temperature was similar and each day I drove to work on clear highways/streets midday and into the afternoon. It was an inconvenience for several mornings and I drove home twice on snowy freeways at midnight. I;ve got a file for that one too!

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