If you were to look up "Seattle Snowstorm" in the various weather textbooks, you'd find it talks about arctic air coming down from the north, meeting with a moist warm weather system coming in off the Pacific Ocean, and all that rain falling into the arctic air and turning to snow. Sounds simple, doesn't it?
Well, apparently Mother Nature doesn't have that textbook. Or, perhaps she's considering writing some new chapters.
We once again have another challenging and somewhat unique weather scenario playing out that, if it goes according to computer forecasting model plan, could bring a return to the snow to some areas of the Puget Sound area -- although it appears most, including Seattle -- will miss out.
I know, I'm with ya. After the past week, you're ready to punt those mind-changing why-can't-they-ever-get-it-completely-right computer forecasting models into the Puget Sound, or, at least subject them to watching the bad auditions on American Idol.
But, the models are right more times than you think, and when they're all kind of singing the same tune, you have to take notice (even if Simon Cowell doesn't).
So, the latest forecasting model snow scenario du jour shows an area of low pressure once again developing up in southeastern Alaska and sliding south/southeast through British Columbia Tuesday and then turning to the east around the Washington/B.C. border near the Okanogan Mountains Tuesday night, dragging an arctic front behind it as it comes along. This would likely begin as increasing clouds late Tuesday, with rain developing first early Tuesday night before we cool off and get into the fun stuff.
The potential scenario presents three weather challenges (well, three-and-a-half) for those that live around here.
One: The Wind
The first is the wind. Depending on the strength and position of the low (and the models have it in a pretty good position), that low could draw down some strong westerly winds down the Strait of Juan de Fuca, barrel over Whidbey Island and Admiralty Inlet, then blow through the greater Everett area before crashing into the Cascades. Right now, wind speeds look to be in the 25-40 mph range, with perhaps higher gusts. (So, it's windy with a twist. Instead of those frigid easterly Fraser Winds of the past few days, we'll have strong west winds.)
One (and a half): Colder Air
That front is also going to drag in some colder air behind it. Not too cold, but we don't need to get much colder to get back to the snow line.
Two: A Convergence Zone +Foothill Snow
As that front passes and the Strait winds die down a tad toward Wednesday morning, we're looking at pretty favorable (OK, textbook) conditions for a very strong convergence zone. Combine strong convergence zones with cool air near freezing, and you've got the recipe for some snow. This would be a somewhat-localized area of a line from Shoreline to North Everett stretching east to the Cascades -- although the exact location of where the Zone will set up is still a bit in question, but the aforementioned area is the best guess.
Forecasting snow totals right now would be fruitless, since they'd be sure to change. But I saw one National Weather Service forecaster term it: "anything could happen from the sublime to the ridiculous." So, even though the snow flag is likely battered from overuse, we're raising it again for the Convergence Zone areas late Tuesday night and into Wednesday morning. (Yes, this means Everett could be in the double whammy of gusty winds and snow.)
It's also possible the winds will be so strong, they'll shove the Zone over toward the mountains, sparing the main metro areas of any snow and leaving us gusty but mainly dry. We'll check on that Tuesday.
Either way, the heavier accumulations would be in the Snohomish County foothills and -- to a lesser extent -- the King County foothills.
A WINTER STORM WATCH is in effect for that area Tuesday night and early Wednesday morning. The WATCH says 2-4" in the central Cascade foothills are possible (remember, a WATCH means conditions are right, but not certain. A WARNING would mean it's no doubt coming, or is already happening.), with the potential for 6+" in the Convergence Zone foothill areas of Snohomish Counties. (But remember, I'm not forecasting snow totals :) )
Three: Mountain Snow
With all that wind crashing into the Cascades, then ramping up the hills and squeezing out their moisture, skiers finally -- FINALLY -- FINALLY! -- have a recipe for a good ol' fashioned mountain snow storm. A WINTER STORM WATCH is in effect for the mountains too for Tuesday night. Here, we're looking for at least a foot of new snow. But on the flip side, this will make pass travel dangerous -- especially Snoqualmie and Stevens. With the heavy snows comes the strong winds and blowing snow, so Tuesday night is not a good time to be crossing the mountains.
Four: Elsewhere (Hey, look, I can be a miscalculating computer model too!)
For the rest of the area, including the Downtown Seattle/Bellevue/Tacoma areas and other points outside the Convergence Zone, we're looking at mainly rain, or perhaps a rain/snow mix as that colder air moves in, but we won't have as much moisture nor does it look like we'll quite have enough cold air, as general snow levels outside the Convergence Zone look to drop to only 500 feet. So not looking at any accumulations except maybe a little on the highest hilltops.
If this sounds complex and like a lot of things have to mix together just right for this to happen, youre right. Its like walking the weather tightrope one little change could knock this forecast off the wire. (Maybe I can make one of those "small print" paragraphs standard here about how these models can change and how they're not valid in Vermont and don't require a purchase and the like...) Anyway, we'll keep track of it.
Some snow lingers into Wednesday midday before we dry out and get sunny for the rest of the week. (Skiers, Thursday and Friday might be the best skiing conditions you've seen in AGES!)
Speaking of which, We're expecting sunny skies Thursday through Saturday, but still kinda chilly. Highs will only be in the mid-upper 30s and lows will drop into the low-mid 20s in Seattle, and colder in the outlying areas. We finally begin to warm up toward the start of next week, with plain ol' rain returning for Sunday and highs into the downright balmy mid 40s.
In the meantime, I'm taking Mother Nature's pen away. We've seen enough crazy snow scenarios for one winter :)