Lowland snow possible late Sunday into Monday

For the first time this season, the low-elevation spots around Western Washington -- including all of Puget Sound -- have a shot at some accumulating snowfall to end the weekend.

The weather pattern is pretty typical: a low pressure system offshore which provides a moisture source while "pulling down" cold air out of British Columbia.

The question with these weather patterns always seems to be, "Will we dry out before we get cold enough for snow?" And indeed it is with the forecast for Sunday afternoon into Monday morning.

But more than a month late in this fall and winter season, snow for some looks like a real possibility and we'll take it!

Sunday up north

This Sunday surge south of cold air through the Fraser Valley of British Columbia will be strong enough to create some really gusty conditions around Bellingham and around the San Juans, but the actual "coldness" of the air isn't anything really too remarkable. %

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That said, it should still be cold enough for some rain/snow mix in low elevations -- or even turning to all snow at times -- Sunday afternoon through Sunday evening north of Everett. The farther north, the colder it will be late Sunday and the better the chances of snow instead of rain.

Amounts -- at this still-early stage on Thursday -- look light at best but we will be watching for potentially some heavier snowfall totals along the leading edge of the southward-moving cold air. It's impossible to determine at this point if and where that would set up. We could also get heavier totals in the favored upslope locations of Whatcom County like Lynden and Sumas.

Sunday night into Monday areawide

It looks like it'll probably be cold enough for snow in most lowland locations -- including the larger cities around Puget Sound -- late Sunday night into Monday morning.

The problem is: right now it looks like the moisture will be drying up so the best meteorological shot is to call for some snow showers around the Sound for that period. The word "showers" would mean "pockets of snow" instead of a solid area of snow that covers the whole region.

Having just mainly-light snow showers around will create the typical forecasters' headache: some folks might get an inch or two of snow while others get absolutely nothing. That seems to be what's on the table, at least as things stand as I write this on Thursday evening.

But all these are still just the best-estimate

and not the official final forecast, which will come over the weekend.

Why don't you know yet?

It's all a matter of size. The scale of the weather pattern. The larger the weather pattern or weather feature, the better we are at accurately forecasting days in advance. %

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The more you zoom in to smaller weather features -- like exactly who will get snow and how much -- the more difficult the task. In fact, more than a day or so out in a weather situation like this, it's nearly impossible. It's just beyond the capability of forecasting in the challenging Northwest weather environment. (And sometimes things go awry within a day!)

The forecast will firm up every 12 hours as we get closer. (We get new forecast data to crunch about every 12 hours.)

But going back to looking at larger weather patterns, we do know that this airmass coming in is the coldest of the season and will bring highs only in the 30s Monday and Tuesday!

So what can you give me now?

I think it's safe to day that conditions will be favorable for lowland snow Sunday into Monday. It looks like the better chance of accumulations that might be significant (like more than a couple inches) will be north of Everett but that could change. %

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Across the rest of the area, kids can still be hopeful but it really looks like the moisture will be so lacking Sunday night into Monday that some pockets of snow will be around but nothing widespread or major.

That's the consensus of forecast models at this point on Thursday, though I will say there is one forecast model that is more aggressive with heavier snowfall. It's the only one at this point but we'll watch and see if it comes in line with the majority of models that are pretty minor with spotty accumulation or if the majority start to move toward that heavier outlier.

Such is the fun (!) forecasting snow in the Pacific Northwest!

Bottom line: We will probably see snow somewhere late Sunday into Monday. Who gets snow and how much, and who gets nothing? Can't tell yet.

I'll see you on KIRO 7 News with updated details.

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