It’s been said that “snow is the most difficult thing to forecast in the Pacific Northwest.” And while I believe this is often true – our terrain, microclimates, and often marginal temperatures can make snow forecasting extraordinarily challenging – I think a corollary is more appropriate. Lowland snow forecasts are, without a doubt, the most difficult thing to communicate in the Pacific Northwest. And as I’ve stated so many times on this blog, forecast communication is what really matters.
A classic example of the city going berserk over what turned out to be a measly snowstorm was the “Great Kale Shortage” of 2019. When I think of panic buying, I generally don’t think of kale, but I guess Portlanders take their leafy greens seriously.
Pre-snowstorm in Portland, the only thing sold out so far at the grocery store was kale. Plenty of bread and milk remain. #pdxtst pic.twitter.com/grYk1EaVj4
— Jesse Friedman (@JesseCFriedman) February 8, 2019
There have been some rumors flying around of snow on Sunday and early next week. Of course, there’s a massive difference between a few non-sticking snowflakes falling through the air and a crippling, sled-worthy blizzard, and that massive distinction can often become obfuscated when snowflakes appear on your weather app.
In this blog, I’ll dive into the specifics of when, where, and how much snow the Portland metro area is expected to receive. But before we do that, let’s take a quick look at the current conditions and Friday/Saturday forecast.
We currently have an upper-level trough diving SSE off the California/Oregon border. This trough is a treat to view on satellite and is shown by the swirl of clouds offshore.
The counterclockwise flow around this system is helping pump a few light showers northward, but most are over the Coast Range or offshore. In any event, these showers will decrease and move south overnight as the trough weakens and continues its slow trek towards SSE towards the central California Coast.
Credit: University of Washington
Friday should feature clearing skies as this trough continues to move out of the area, and Saturday should be spectacular with sunny skies to begin the day and just a few high clouds by sunset, although there may be some areas of patchy morning fog across the I-5 corridor, including the Portland metro. And with clear skies Friday night/Saturday morning, Saturday morning lows could be the coolest of the year, dropping into the upper 20s even in the city center and the mid 20s in outlying areas away from the city.
Our first chance of lowland snow arrives Sunday as a rather strong cold front arriving from the northwest moves into the pre-existing cool, dry airmass. Precipitation will likely begin as snow Sunday morning, but nothing more that a dusting is expected below 1,000 feet. Still, the West Hills and maybe even the top of Mt. Scott could see a quick inch or two Sunday morning before precipitation turns to a rain-snow mix in the afternoon. The Cascades should absolutely see heavy snow from this – I expect that winter storm warnings will be issued and that Government Camp may see as much as a foot of snow by Monday afternoon.
Monday will be cool with a few showers in the wake of Sunday’s cold front and I can’t rule out a stray snow shower down to the valley floor Monday night/Tuesday morning, but again, I’m not expecting anything more than a dusting below 500-1000 feet. Our next real shot at snow arrives on Tuesday evening/Wednesday morning, and the threat is still pretty minimal, albeit slightly greater than Sunday. On Tuesday night, a stronger system offshore should spread some precipitation into Western Oregon, and with a cool airmass in place, this precipitation could begin – and possibly stay as – snow.
The location of Tuesday night’s system is crucial. The “ideal” pattern for lowland snow with Tuesday night’s system is to have this system due west or WSW pf Portland. This keeps it close enough to spread precipitation inland while creating strong offshore gradients across the Cascades, allowing cold, eastside air to pour into Portland and keep precipitation in the form of snow, sleet, or even freezing rain. On the other hand, if this system ends up being too far north, the counterclockwise flow around the system will send mild, southerly winds through the Portland area, completely erasing any snow chance below 1,500 – 2,000 feet.
Some model runs like the UW WRF have shown this low being in a favorable position for lowland snow. However, the ensemble forecasts are all over the place with this low. It’s always frustrating when the “deterministic” models (like the UW WRF, which run at a higher resolution and have plenty of amazing weather graphics) show a more severe solution than the ensembles, as these weather maps make their rounds on social media and give the public the impression that snow, wind, or the hazard du jour you is more likely and severe than it actually is.
Credit: Weatherbell
If Tuesday’s system is positioned exactly right, there is a chance we could see an inch or two of snow all the way down to sea level in Portland. However, a much more likely outcome is that precipitation will be in the form of non-sticking snow below 500 feet, with light accumulations above 500 feet. The exception is the Columbia River Gorge east of Corbett, where cold air will e more entrenched and at a small amount (1-3″, higher as you head east) of snow is likely.
Credit: Weatherbell
Wednesday should be slightly milder with showers, and by the end of next week, we should transition to a milder and wetter pattern with near or slightly below-average temperatures, above-average precipitation, and a steady parade of storms coming from the WNW. This is a classic La Nina pattern and would result in copious amounts of mountain snowfall.
Credit: WeatherTogether Models
So in the likely scenario that Portland sees some snow in the air Sunday & Tuesday night but no accumulations on the ground, one can always head to the mountains to see tons of fresh powder. The Oregon Cascades are currently well below average (50-70%) of their yearly snowpack, but they should make up some of that during the last few days of January and the odds favor a snowier-than-average February due to the current La Nina.
So to summarize, snow in the air is likely on Sunday morning and Tuesday night, but snow on the ground is unlikely below 1000 feet on Sunday morning and 500 feet Tuesday night/Wednesday morning. There’s still plenty of time for Tuesday/Wednesday’s system to change though, so even though accumulating snowfall is unlikely for downtown Portland, we can’t rule it out completely. And next week’s system – more so than Sunday’s, has a threat of winter weather east of Corbett and even more so once you head east of Cascade Locks.
That’s all I have for tonight. Enjoy the beautiful weather Friday and Saturday, be on the lookout for some snowflakes Sunday morning, and do some intricate snow dances to see if we can make Tuesday’s slim chances of accumulating Portland snow come to fruition!
Charlie
