Puget Sound Weather Outlook
Updated Monday 8:40 a.m.
Weather Headlines:
Here is the news in a nutshell:
- Snow showers will fall through the day.
- Winter Weather Advisory expanded to include Seattle/Tacoma/Bremerton/Everett metro areas and is in effect until 6 p.m.. Advisory now covers all of Western Washington except north coast.
- Snow accumulations are expected to be around 1-2", but some spots, especially above 400 feet and east of Lake Washington, could receive closer to 3-4".
- Enhanced area of snow showers expected in North Sound in mid-late morning, then moving south into Central Puget Sound around midday/early afternoon, then South Sound in afternoon/early evening.
- Strong winds begin to blow out of Fraser River Valley through Tuesday, making for cold temperatures and bitterly cold wind chills.
- Lows Monday night will likely near records -- into the upper teens and low 20s
- Slow moderation toward the end of the week.
The Details:
An unseasonably strong arctic air mass is working its way into British Columbia, which will push out through the Fraser River Valley up near Bellingham during the day Monday and keep pouring out through Monday and Tuesday (think of it as an icy blow dryer.)
This arctic air will meet up with some moisture spinning around a weak area of low pressure that is dropping south along the coast, giving us a continuing chance of snow as the day progresses.
A WINTER WEATHER ADVISORY has been expanded now to include just about all of Western Washington -- including the greater Seattle/Tacoma/Everett metro areas -- but excluding the north coast and western end of the Strait of Juan de Fuca. This advisory is in effect until 6 p.m.
Generally speaking the snow totals will range from 1-3", with the higher hills east of Lake Washington above 400 feet falling more into the 2-4" category. (Check your elevation at this link
However, snow totals will vary a bit across the region as this snow is more a showery hit-and-miss pattern, rather than a wall of widespread snow. Sort of like dumping a bunch of marbles on map, and wherever those marbles roll are where the snow falls.
The Meteorological Mumbo-Jumbo
As usual with snow in the Northwest, and especially in March, it's a complex situation.
The main event is a large, deep pool of arctic air that is working its way south into British Columbia.
http://bimedia.ftp.clickability.com/...ctic_temps.jpg
In addition, we have a weak area of low pressure moving down along just ahead of the boundary of this arctic air. That will add some moisture in to the mix.
Overall, this low will spread some showers around, and those are the random snow showers we've been seeing early Monday morning. Those can put down a trace to 2-3" as they pass. The immediate Seattle-Everett-northern Kitsap corridor was being shadowed a bit from the Olympic Mountains, but that protection will fade away as the day progresses, bringing this area into the snow as well.
But as the cold air starts pushing out of the Fraser River Valley near Bellingham, that will create some convergence between the cold north wind and the slightly milder west wind that's wrapping around the low now.
It's not quite a classic Puget Sound convergence zone, but it works in a similar way that where these two winds collide and can create lift.
In addition, this boundary of arctic air can enhance showers in its immediate area as well. Since this colder air is heavier than the relatively warmer air it's running in to, the cold air shoves itself underneath the warmer air, causing it to lift and then condense into clouds and snow.
So the trick to watch for today is when this arctic boundary begins to make its trek south from Bellingham down the I-5 corridor through the Puget Sound area and then into the south Sound. It is along this boundary where we will see frequent, enhanced snow showers (it doesn't look like it'll be a wall of snow, but just an area where snow chances will be higher.) To use my earlier analogy -- think of it as an area where more marbles will be dumped on the map.
For timing, it appears this zone will be in the far North Sound around late morning, then into the Central Puget Sound area in the midday to early afternoon hours, and then into the South Sound by late afternoon or early evening.
As we mentioned earlier, these showers could put down a dusting to 3" in the lower elevations near Puget Sound (i.e., greater Everett-Seattle-Tukwila area) and perhaps a little higher amounts to 3-4" in the eastern hills above 400 feet and as you get farther east away from the Olympics, and perhaps a little more as the boundary drifts south of Seattle toward Tacoma and Olympia and picks up a little moisture.
And just to make it even more interesting, it's possible some of these showers could have some thundersnow
See, told you it was complex :)
Aside from that, we have one other area to note: The eastern Strait of Juan de Fuca area is in the snow advisory because once that cold northeast wind starts pouring out of the Fraser Valley today, it'll run into the northeastern side of the Olympic Mountains, creating an area of enhanced snowfall right along US 101. Could see an inch or so along the water, but up to 3-4" as you get into the higher Olympic Mountain foothills south of Port Angeles, Sequim and Gardiner.
Meanwhile, skies will clear behind the front later this afternoon, and strong northerly winds will follow, dropping temperatures a bit. This could make for an tricky evening commute for any spots that got a decent amount of snow -- at least until the initial traffic melts off some of the snow. Monitor the radar and forecasts through the day Monday and we'll provide frequent updates.
Monday Night: Clear and Very Cold
We clear out Monday night, but that will allow temperatures to drop to near record low levels - into the upper teens around Bellingham and low-mid 20s elsewhere. Northeast winds will blow around 20-30 mph near Bellingham, and 15-25 mph elsewhere, adding wind chills to the equation.
Another Chilly Day Tuesday
Cold air remains entrenched Tuesday, but at least it'll be sunny. Highs will only reach the upper 30s, and then lows Tuesday night will again be in the 20-23 degree range, perhaps even colder in Bellingham.
Slow Moderation:
The winds will slowly subside out of the Fraser, allowing us a slow warm up. Wednesday will be dry but still chilly, with highs in the low 40s and lows in the 28-30 range. We warm back up for Thursday and the end of the week, getting closer to 50.
However, really long range forecasts drop us back into the 40s the following week.
Scott Sistek
KOMONews.Com Meteorologist
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