Friday, December 30, 2016

New Year's Eve Snow for the Puget Sound Lowlands?

I will have an Update at 1 PM Saturday-still looks like a light snow event after midnight... strong winds tomorrow over NW WA.  And much colder.  More later.

Confidence is high in a transition to much colder temperatures over the Northwest starting on Sunday, but what about lowland snow around Puget Sound?

Will there be snow flakes flying as folks return home from their New Year's celebrations early Sunday morning?  Perhaps...but not too much.

The general situation for Saturday/Sunday is clear.   As shown in the upper level map for 4 PM on Saturday, an upper level trough will move southward over the Northwest (with ridging over the Gulf of Alaska).  The trough will provide upward motion that brings clouds and precipitation, and as it passes, cold arctic air from the continental interior will sweep south and west over our region.


By 1 AM Sunday morning, cold air (blue colors in surface chart below) will be moving into Washington State, with a trough of surface low pressure just south of Seattle.

At 10 AM Monday, very cold air has spread over the Northwest, with easterly flow pushing the frigid, arctic flow over the Pacific.


Although we will have both upward motion and cold air, the configuration above it not ideal for much snow.  For substantial Puget Sound snow one wants the upper trough to extend farther offshore, with the associated surface low moving southward along the coast.  That would both draw cold air southward and provide precipitation at the same time.

So what do the models show?  The European Center ensemble (many model) snow total prediction for Seattle suggests only light snow, mainly after midnight--perhaps .5 to 1 inch.   A much greater risk is suggested for next weekend (roughly 6 inches).

The high-resolution European Center snow forecast through 4 AM Sunday shows light snow over the west (0-1 inches around Puget Sound near sea level, 1-2 inches near the Cascade foothills.

The National Weather Service (GEFS) ensemble forecasts shows a mean snow total around 1 inch by Sunday AM.  This is snowfall, not snow depth.

So the bottom line in all this is that you should expect increasing clouds on Saturday as the trough approaches.  Light rain will begin over the lowlands around dinner time and then transition to snow showers between 10 PM Saturday and 1 AM on Sunday.   A few hours of light snow will follow before the atmosphere dries out on Sunday in the cold air.   Much of the lowland snow will be focused on a Puget Sound Convergence Zone over north Seattle and the arctic front--the zone of transition to the cold, continental air.  Most of the region will end up with little to perhaps an inch of snow.  Not a big event, unless our forecasts are way off.

As noted earlier, the cold forecast for next week looks solid... the coldest period around here since December 2008.   The latest European Center forecasts for high and low temperatures at Seattle suggest highs near freezing and lows in the mid to lower 20s for Monday through Thursday.  Teens in cooler locations away from water.


Good time to remove exterior hoses, protect faucets, and block exterior vents.  And keep pets inside.

13 comments:

Jondroot said...

Here's to hoping the forecasts are way off :)

Richard said...

Agreed!

John said...

Nice coverage regarding the possible weekend snow and PSCZ this afternoon on the Weather Channel!

Jerry said...

I'm still new to the area, what does light snow on New Years' Eve say about ice on highways and hills around that time, or through to Sunday morning?

Joseph C. said...

The 500mb, there is a blocking high over the the gulf of Alaska and is expected to be there/persist for a long time. This configuration is similar to 17 Dec 2008.

tracksdc89 said...

Hopefully, these repeated, "once-in-a-few-years"-type cold-weather assaults our area is continuing to endure, already now at only the beginning of winter, is enough to satisfy the many readers who, in great frequency, voiced their concerns about the "blob" (or other causes) resulting in winters here that were considered to be too mild. Unfortunately, unlike in the Midwest and Northeast, much of the housing in this area is simply not built to withstand these repeated blows of far-below-normal temperatures and can result in serious health issues. Sadly, those who can least afford it are usually the most severely affected. And, as we are now seeing, severe cold does not necessarily equal copious and pretty snowfall - the sad truth is that it negatively affects the well-being and quality of life of our most vulnerable. It may not be trendy to say this, but I am hoping that this upcoming cold spell will be the last of this winter.

Charles Nathaniel Erwin said...

Agree Tracksdc89 about cold weather housing. My father's house in Federal Way build in 1959 it toasty warm on the coldest of days and will retain heat for several days after a power outage. My fancy condo in Redmond is a leaky icebox in the winter and a sauna in the summer.
That said, happy to see the cold. The balance in nature around here is kept with a cold blast once a year from the Seattle Rat problem to spring mosquitoes. Bring on the cold.

windlover said...

Please say the forecasts for next weekend are wrong! They were saying the highs were still in the low 30's...still cold enough for snow. Now they are saying mid to high 30's with a chance of rain during the day :-( I really was looking forward to a few days of snow before the warm up...my hopes are slipping away...

Deek said...

It will feel much warmer if the Huskies win today-go Dawgs.

Garry Klouzal said...

I see there is a winter weather advisory for western whatcon and skagit counties for 3 inches of snow Saturday night.

Stickerbush said...

Snowing on Vashon Island now (12:50pm).

Stickerbush said...

Radar shows an interesting snow blob over the Sound, covering Vashon, Bainbridge, and western edge of Kitsap. I've been watching it for almost an hour and it's not moving much at all, just sitting over this area, increasing in size a bit.

Snow is starting to stick here on Vashon.

Scott K. said...

Light snow at 1:30pm in Auburn.

@windlover

This goes back to my question of why/how the forecasts continue to start off showing an event, but as we get closer to the event they downplay it right at the last moment. It seems to happen with wind and snow events, and in this case possibly the cold event that's coming tomorrow.

I can't remember a time when a forecast talked about a future storm and actually upgraded the strength as we got closer. They've always downgraded as we get closer, which I think has a lot to do with people's opinions on accuracy and 'cry wolf' stuff that's been talked about lately.