A Very Tricky Snow Forecast Today, More Snow Possible Later This Week

Snow is falling over Western Washington and parts of NW Oregon this morning. I’ve been riding the train down from Seattle to Portland and saw close to an inch in the higher elevations near Centralia. I’m now in Kelso and everything has switched to a cold rain, with no snow accumulation to be found.

This snow has been courtesy of a frontal system bringing precipitation into a near-freezing airmass. As the day goes on, temperatures will warm and increasingly strong southerly winds will help scour out this cold air from south to north, but exactly how much temperatures will warm – and where they will warm – is highly uncertain. The current forecast is for a rain-snow “boundary” to make its way north throughout the day and stall near the Seattle-Everett area this afternoon, with precipitation remaining as snow to the north of this line and rain melting any of the light morning snow that may have fallen to the south of this line. Temperatures may surge above freezing everywhere shortly after midnight – even north of Everett – as the storm’s warm front moves inland, but by then, several inches of snow will likely have fallen over North Puget Sound. It’s a very tricky forecast.

Here’s what we know so far.

1. As mentioned above, a very complex frontal system is moving inland this morning. Many areas started out as snow but will switch to rain this afternoon, while other areas will stay as snow throughout the event. This “rain-snow” line is currently predicted to be right over the Seattle area, which makes forecasting amounts a real headache. That said, here’s my best guess at this time:
   • Olympics and Cascades: up to 1-2 feet. Winter Storm Warning in effect.
   • Kitsap Peninsula and Hood Canal: 1-6+”, highest north and east. Winter Storm Warning in effect. The easterly winds ahead of the storm tend to both trap cold air up against the Olympics and provide orographic enhancement of precipitation in the Hood Canal Area.
   • East Puget Sound Lowlands: 1-6+”, highest further east towards the Cascades with elevation. Winter Storm Warning in effect.
   • Rest of Western Washington: trace-4+”, with less snow south and more snow north. Winter Weather Advisories in effect from King County North, no snow advisories Tacoma south (except foothills).
     • Tacoma should just see a trace and will mostly see rain after light snow this morning
     • Everett could see up to or potentially exceeding 4″ and should mostly see snow throughout the event.
     • Seattle is expected to be right on the “boundary” between this rain/snow line, so amounts could be anywhere between 1-4,” with higher amounts likely north and lower amounts likely south.
2. This system will pack some strong winds this afternoon and evening. Wind advisories are in effect from South Puget Sound up through Snohomish County, and High Wind Warnings are in effect for Whatcom, Skagit, Island, and San Juan Counties. Winds are expected to reach 40 mph in areas with wind advisories and 55 mph in areas with High Wind Warnings, and winds these strong could cause power outages, especially in areas with snow on the trees. Winds will increase this afternoon, peak tonight, and slowly subside Wednesday morning.
3. Cold-ish weather will continue through early next week, with additional chances for snow Wednesday night/Thursday morning (mainly over SW Washington) and Friday/Saturday morning. Next week and beyond looks very chilly with ample mountain snow but I don’t see any bona-fide arctic outbreaks on the horizon.

Current Conditions

The current satellite and radar imagery show a rapidly-developing system sweeping in from the northwest. We are currently experiencing light precipitation and weak southeasterly winds in most places ahead of this system’s warm front.

Temperatures are currently on either side of freezing for most of Western Washington. Eastern Washington is much colder, with widespread single-digit temps over Mazama. The Cascades are very effective at shielding Western Washington from true arctic air.

This storm is undergoing rapid cyclogenesis, although it is difficult to see on satellite due to high clouds obfuscating its development. The below image shows the storm as modeled at 7pm this evening – note the strong isobars and how warmer air has poured into Western Washington. The tight isobars correlate to strong winds near the center of the storm, and the warmer air marks the passage of the warm front east of the Cascades.

Snow forecast:

This is a particularly difficult snow forecast for Western Washington, especially north of Seattle. And that’s saying something, since even our relatively “easy” snow forecasts involve a bit of dart throwing! As this intensifying storm and associated warm front move inland, they will scour out the cold air over Western Washington, resulting in a changeover to rain. However, there are certain areas where this cold air will be more stubborn – such as Hood Canal and Northern Puget Sound, which will likely see all snow. The lowest confidence is in areas like Seattle, which are right on the boundary between having this mild, Pacific, warm-frontal air mix out the cold air already in place.

As this system progresses inland overnight and southerly winds peak, the “tongue” of warm air behind the storm’s warm front will push further north through Western Washington. By then, North Puget Sound will likely see a brief period of partial melting as southerly winds strengthen, milder air creeps northward, and temperatures rise above freezing. Check out the temperatures at 925mb (~2,500′) at 4am Wednesday morning, and note how above-freezing (green) air has made it all the way into southern BC.

That same model shows quite a bit of snow over Everett over the next 24 hours, with any snow switching to rain by 1-2 am at the lowest elevations while the foothills stay snowy.

Another system will approach the area Wednesday night, and unlike today’s system, the uncertainty lies in precipitation, not temperature. Currently, the system is expected to make landfall along the NW Oregon Coast deliver several inches of snow to SW Washington while NW Washington stays dry. Seattle will once again be on the fringe.

Yet another system will bring a chance of snow Friday and Saturday morning. Current models have this system stalling offshore but bringing strong easterly winds through the Columbia River Gorge, which would be a classic snow/sleet/freezing rain event for the Portland metro area. Confidence is still low this far out so stay tuned.

This cold, occasionally snowy pattern will persist through early next week, with systems from the NW clipping the area and bringing a mix of chilly rain and mountain snow to the Pacific Northwest. As the ensembles below show, we’ll likely moderate somewhat by later next week but still remain cooler-than-average with ample mountain snowfall. There haven’t been any consistent signs of arctic air making it into the I-5 corridor, but some snow in the lowlands can’t be ruled out.

Enjoy the first widespread lowland snow of the 2022-2023 winter. Hopefully there will be more to come!