Snow In The Air, Plus a Bit of White On The Ground For Some This Week

1pm Monday…

We’ve seen lots of cold showers/rain the past few days. I just went cross-country skiing on the back side of Mt. Hood yesterday and it’s amazing! From nothing 5 days ago to 3 feet of fresh snow on the ground. It’s like January conditions just suddenly arrived after a warm fall/November. Timberline, Meadows, & Mt. Bachelor ski areas are operating, and Skibowl opens Wednesday. Right now about 40″ is on the ground above 5,000′ and about 2 feet at Government Camp. Nice!

Many of us have seen snowflakes mixed in with the rain at times, especially in the hills. In fact snow fell for several hours on the valley floor this morning from Corvallis down to Eugene. The view around 10am at OSU

Temperatures were near/above freezing, so no driving issues, but…

THIS IS WHAT I EXPECT WILL HAPPEN AGAIN WEDNESDAY MORNING, BUT FARTHER NORTH IN THE VALLEY, INCLUDING THE PORTLAND/VANCOUVER METRO AREA.

First, a summary in case you are a TLDR type of person

WHAT I EXPECT

1. Any showers this evening through midday Wednesday could be mixed with snow ANYWHERE in our viewing area
2. Late this evening through late tomorrow night will be mainly dry! Nice Tuesday ahead
3. Watch out for icy spots on some roads late tonight if some wet areas freeze. It’ll be spotty
4. Wednesday morning (4am-10am) a weather system moves inland, and most of us see at least a mix of snow/rain, with temperatures above freezing
5. There could be spots where it drops TO freezing at that time and snow sticks briefly. Especially far west metro, West Hills, Chehalem Mtn, Amity/Dundee Hills, South Salem Hills. You get the idea, elevation will help a lot, plus being closer to Coast Range too. Maybe 1-2″ in those spots, especially 1,000′ and above.
6. Wednesday afternoon through next weekend anything that falls will be rain only

WHAT I DON’T EXPECT

1. SNOWY DRIVING IN 95% OF METRO AREA THIS WEEK
2. No cold arctic air = no big freeze of any sort in sight for at least the next week. That takes us through the 21st. Just some overnight frosts
3. A big/widespread snow event. Just not cold enough or the right weather pattern.
4. Freezing rain. We don’t have a cold east wind with cold air east of the Cascades through at least this weekend.

MEASURING SNOW

I just put out my “snow board” today. Actually an old tile we never used in a remodel. When you measure snow, make sure it’s on a hard surface, not in the grass. If you measure in grass, where would you start? Down at the ground level would be cheating because snow starts accumulating higher up. Anyway, maybe we will get lucky and it’ll get up to that 18″ mark this year! It goes to 24″…just in case

DETAILS

The current weather pattern really does remind me of winter 2007-2008. That year we had multiple “close calls” with low elevation snow, and it snowed at LOT at 1,000′ and above. Yet PDX officially never had more than a trace. I had 39″ at 1,000′ in the foothills. Lots of cool systems coming in from the northwest (Alaska) that year. Right now that is the case with a cold upper-level trough just offshore and about to come inland. Tomorrow it moves overhead with that chilly air, but no much moisture for showers.

That #2 trough arrives Wednesday, and then is overhead by sunrise Thursday.

This is a perfect setup for lower elevation (sticking) snow, but not necessarily on the valley floor or sea level snow. There’s no cold/dry arctic air coming down from the north, it’s all coming across the 50 degree Pacific ocean. But Wednesday morning that trough spins up a surface low pressure system west of us.

That gets rid of the mild southwest wind and we should be calm or see a light easterly breeze at that point. That CAN allow snow levels to lower to sea level if the precipitation is heavy enough. No surge of cold air is coming from anywhere, thus this is a “marginal” snow “event” for us. A stretch one could say!

Notice the GRAF model (IBM) Wednesday at 4am. A few degrees above freezing in the lowlands as light precip arrives.

Then at 10am what you don’t see is southerly wind overhead as the low approaches. Temps just a bit too warm for sticking snow for most of us.

After this point, it’s too warm overhead to support snow below 1,500′ or so. I think the WRF 1.33km snow accumulation product shows exactly what I’m thinking

A dusting possible in any of those locations I mentioned earlier. Probably first sticking snow of the year top of West Hills, maybe parts of Clark County? Basically a less intense version of that January 26th snowfall last winter. Except we had a lot of evaporative cooling that day; that’s not happening this time.

That surface low moves almost right over Portland late Wednesday night, pulling up plenty of (slightly) milder Pacific air. Just enough to pull the snow level up to 2,000′ overnight and into Thursday.

I don’t see any other “close calls” through at least next Monday. A wet system with gusty south wind arrives Saturday, then models imply a significant upper-level trough may split as it moves toward the Pacific Northwest NEXT Tuesday. Flow remains cool, but no sign (for now) that anything BIG will be happening in the next 7-8 day other than Wednesday’s close call.

I’ll be watching closely of course. And those Canadian ensemble forecasts support a “no snow in lowlands” forecast through this time. Maybe something closer to Christmas, maybe.

Chief Meteorologist Mark Nelsen

This entry was posted on Monday, December 13th, 2021 at 1:09 pm and is filed under Weather. You can follow any responses to this entry through the RSS 2.0 feed.
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