Spotty New Year’s Snow, Bigger Event Late Next Week?

New model runs are coming in as we speak, and they show a similar scenario for late New Year’s Eve/New Year’s Day. Next week still looks like the coldest in several years, and there is low confidence in a moderate-to-major snowstorm on Friday, with model solutions agreeing on bringing a system into the area while cold air is still in place but varying greatly on the details. We could see even more snow the week beyond, but there’s very low confidence in the extended due to poor model consistency.

Let’s start with New Year’s Eve/New Year’s Day. Models have trended a tad later with this system, showing light, scattered snow beginning around the region very late Saturday night and dying off a couple hours before sunrise Sunday morning. The thinking has not changed that this will be a minor event, with a trace to three inches for most folks, with higher amounts further north and lower amounts further south. As I talked about in last night’s blog post, the scenario is somewhat favorable for a Puget Sound Convergence Zone to set up, but models have been inconsistent in actually showing a convergence zone forming.

Here is the latest chart showing the winds at the surface, the sea-level pressure, and the temperature at the 925 mb pressure level of the atmosphere (approximately 2,500 feet). We have a very weak low pressure system just to our east, giving us a little moisture and ushering in a much colder air mass.

Compared to last night’s, this low is slightly weaker and further west. However, there are really no major differences here.

The 24-hour snow accumulation over Washington ending at 4 am Sunday is also very similar from last night’s runs to tonight’s, with weak convergence zones over the Northern Interior and Southern Snohomish County. However, this morning’s runs did not show convergence zones, so whether there is still a bit of uncertainty as to whether these will develop.

The bottom line is that this will be a minor event, with most places seeing an inch or less and the Eastern Puget Sound Lowlands, the Northern Interior, and areas inside Puget Sound Convergence Zones (likely Southern Snohomish County) with the best chances of seeing snow. In the aforementioned places, accumulations could reach up to three inches. Confidence is improving that some areas will see snow simply because we are closer in time to the event and models are still showing a chance of snow across Western Washington.

Not much has changed for the Sunday afternoon through Thursday time frame. We remain dry and cold, with strong northeasterly winds flowing out of the Fraser River Valley. Though the Saturday night/Sunday morning system will usher in chilly air, our reinforcing shot of cold, arctic air comes Sunday night.

By sunrise Tuesday, temperatures are absolutely frigid over the region, particularly Eastern Washington. Temperatures will plunge to the single digits on either side of 0 in Eastern Washington Tuesday-Saturday mornings (warmer later in the week), with highs struggling to reach freezing Monday through Thursday in Seattle and lows flirting with the high teens. This would be the coldest weather since February 6, 2014 (4 days after the Seahawks obliterated the Broncos in the Super Bowl), when Sea-Tac reached 29 degrees, but this cold snap would last at least several days longer. Thank you Matthew Charchenko and Wachi Suyaruenkaew for helping me with this statistic!

Temperatures will be even colder in Portland with highs in the upper 20s Monday through Thursday and lows in the mid teens! For my Portland friends, Mark Nelsen’s Weather Blog is a fantastic resource for the latest on our upcoming cold snap, as is the PDX WX Analysis group on Facebook.

I’m still very keen on what happens at the end of next week. Models show us slightly moderating, with northwesterly flow over the area. Under this pattern, cool storms would drop down from the NW. If these storms were to track to our south, we would get northerly winds and cooler air. However, if they are too far south, we don’t get enough moisture.

As the most recent GFS ensembles above show, there is a lot of uncertainty after January 4, and a TON of uncertainty after January 10. The most recent “main” GFS run was fairly insane after January 10, giving us extremely cold temperatures and snow, but it was one of the coldest of the ensemble members. The ensemble “mean” remains below climatology (red line) for the entire period though, which gives us confidence in an extended period of cold. I am confident we will get some snow between next Friday and next week, perhaps a lot, but we still have a lot to figure out before then.

Thanks for reading! I’ll keep you posted!
Charlie