On Saturday, a trough of low pressure sinking south through British Columbia will bring a few late-day showers of snow or rain/snow mix mainly north of Snohomish County, and to the rest of the area after dark. There could be some minor accumulations of snow in Whatcom County into Saturday night but the rest of the area ought to be dry or just see some light rain or light non-accumulating snow for Saturday evening. Highs will be in the 30s to low 40s.
Sunday into Monday: The trough of low pressure sinks south and some colder air filters in. This won’t be bone-chilling cold and will mainly serve to sink snow levels for most of the lowlands of Puget Sound to around 200-500 feet during the day (meaning rain for many low-elevation spots) but down to sea level later in the day into Sunday night and with any heavier precipitation. This will continue into Monday as snow levels sink further to near or just above sea level by daybreak Monday.
The thing is, there’s not a whole lot of moisture to work with on Sunday into Monday. Still, chances are there for some mainly minor snow accumulations of less than two inches across any part of Western Washington in the lowlands.
There is a little better chance of heavier accumulation in any convergence zone that forms mainly north of Seattle during this period, particularly Sunday afternoon into Monday morning. While Monday morning’s commute does not look like a snowstorm by any means, there will be slowdowns and slick spots to contend with.
Some mainly light snow showers will continue through Monday into Monday night before drying up somewhat. This could give a little more snow accumulations to spots, but it’s likely to be spotty and not widespread. It will be colder on Monday with highs in the 30s.
Tuesday could be drier at times as we cool down even further heading into Tuesday night and Wednesday, but the forecast from this point on is very uncertain. Some of the earlier hints of a true “Arctic outbreak” are looking much less likely now as it appears the core of the Siberian cold will move well to the east of Washington State next week.
Still, it’ll be cold enough for snow down to sea level at times Tuesday, so any precipitation will be monitored closely.
From Wednesday through Thursday, I’m calling for periods of “wintry mix” which means rain, snow, or even sleet and freezing rain possible. Forecast models continue to differ wildly on the amount of cold air in places and the evolution of any small disturbances to bring precipitation. The primary U.S. forecast model keeps the lowlands of Western Washington too warm for anything but rain beyond Tuesday, with the exception of Whatcom County. Other forecast models from the European Union and Canada keep more cold air in place and bring more snow and icing potential.
Given the heightened exposure of people during the travel days leading up to Christmas, we’ll continue to note the potential – but not certainty – of impactful winter weather in Western Washington. We believe the forecast to firm up in the coming days regarding the mid/late week period.
It is apparent that by the end of next week leading into Christmas weekend, warmer air will be in place in the Northwest with chances for snow confined just to the mountains. It could be rainy by Christmas weekend with temperatures actually above average by a few degrees – eliminating chances for most of a White Christmas outside the mountains.
Stay tuned for the latest as we get closer to next week, but also we will be focusing on this weekend and early-week snow chances. While it does not look to be a major snow event through Monday or Tuesday, there are likely to be some impacts to travel, especially north of the Seattle area.
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