Sunday, February 10, 2019

A Modest Snow Event Later Today; A Potentially Major Event Later Tomorrow (But Substantial Uncertainty)

Sometimes the atmosphere has "juice".  Lots of vertical motion, lots of precipitation, the potential for a major, problematic event.


Later today we will have a snow event with little juice, but one that we have a good idea of what will happen:  light snow (around 1 inch) sometime after 4 PM.  We have a lot of confidence in that forecast.

But then there is tomorrow.  Later in the day, a much stronger system will approach, with a lot of "juice".   But temperatures will be on the margin, leaving the potential for a "wintry mix" for central Puget Sound southward.   We could also get a major snow dump.  Or we could get mixed rain and snow.  We could get freezing rain over the south Sound.   A lot of uncertainty...and I will try to unravel that in this blog.

We start this morning with some of the coldest temperatures of the winter in many western WA locations (see below, click to expand).  Many areas away from the water were in the teens (even 18F at my location in NE Seattle), and some single digits in colder valleys and the south Sound.   The ground is below freezing and rock-hard ice are on many roadways.


A weak upper level disturbance is approaching (see the clouds over BC in an 8:30 AM satellite picture).  Some low clouds are covering portions of western WA and if you look closely you can see the snow on the image.


Associated with the upper level disturbance will be a surface low (see below) that will cross the northern portion of WA.  Not an optimal position to produce a lot of snow over the lowlands without "juice".


The latest UW WRF forecast (and everyone else's) is for light snow over the Puget Sound lowlands later today (see the snowfall total ending 7 AM Monday).  Roughly an inch, but with heavier amounts over NW WA and in a band south of Seattle.  More near Olympia in the mountains.   A big issue will be downslope flow on the Olympics and the mountains of Vancouver Is:  not rainshadowing but snow shadowing.

And our high-tech, high-resolution UW ensemble forecast of snow at Sea-Tac shows most of the solutions are for about an inch or two, with the majority of the action before 10 PM tonight.

Bottom line.  Light snow will start between 4 PM and 7 PM today.  Light, powdery snow will fall on a cold surface, so melting will be minimal.  With salt, plowing, and a bit of attention, local department of transportations should be able to ensure the main roads are in good shape by commute time tomorrow.  Here at the UW, many of the roads are icy and some buildings don't have cleared paths--attention will be needed to make it ready for tomorrow.

But all this is a warm up for the real-threat tomorrow.

A much stronger system is approaching, with a strong warm front, a well-defined cold front, and much more upper level support.  Much more juice.  The forecast for 1 PM tomorrow shows the sea level pressure and temperature around 2500 ft.  Blue is generally cold enough for snow.


The low will slowly creep towards NW Washington (see same map for 4 AM on Tuesday), with warmer, moist air invading southwest WA, while cold air well be sucked into NW Washington by the differences in pressure (low along the coast and high pressure over southern  BC)


Over SW Washington, precipitation will turn to rain.  Over NW WA there will be snow, and in between there will be wet snow, freezing rain, and everything in between.   

The 24 hour snowfall predicted by the UW system shows this storm, with lots of snow (3+ inches)  north of Seattle, much less to the south.  Huge amounts of snow in the Cascades.



The latest European Center forecast for the same period is generally similar (note that is lower resolution than the UW model).  Mountains get hammered, 2-6 inches around Seattle.


If the temperatures were cold enough, this system would produce a foot of snow, but temperature is the problem.  

But things are more complicated.  Our computer models tend to mix out low-level cold air too quickly, reducing snowfall.  So there could be more.   And god help us if the models are wrong and the low went farther south.  Then we would be talking about the snow apocalypse. 

OK, what is my bottom line with the next storm.

Snow will reach the south Sound in the mid afternoon (around 2-3 PM) and move into central Puget Sound a hour later (3-4 PM).   Snow will be falling during the rush hour.   The evolution will depend where you are.  Transition to rain over SW WA, all snow over NW WA.  In central Puget Sound there may be a transition wet mixed, wintry precipitation during the evening, but there will be at least 3-5 inches of new snow.   If the cold air holds, 5-8 inches.  And expect wet snow, not the fluffy stuff we will have tonight, and a good chance of transitioning to cold rain on Tuesday morning.  What a mess.

Sorry I can't be more definitive...but this one is very hard.  More tomorrow.



80 comments:

Heidi said...
This comment has been removed by the author.
Mass spec guy said...

What are the chances UW opens up tmrw?

B said...

On the edge of my seat waiting to hear.

Mass spec guy said...
This comment has been removed by the author.
bethschubert said...

Thank you Professor!!

Unknown said...

So much uncertainty leads me to believe this may end up being a non event. Are you saying that regardless, Seattle will receive between 3-5 inches?

Just AboveNOAA said...

Don't for a second question whether Kale runs (to the grocery) are predicated upon your wise weather words Professor - because they are. Hell, you may want to insider-trading on Kale futures.

Ron Wodaski said...

A request: the weather map images you are posting are very small, and generally illegible. Any chance you could post larger ones? A goal I would advocate for: the text is legible. :) Or: links to larger versions.

John said...

Sea-Tac set a pair of record lows last night: 25/21 for the 9th and 10th.Very rare occurrence these days,although the previous records were relatively high.
Also,yesterday's storm has not quite cleared the state.Wrap around moisture giving a suprising burst of snow to Spokane/Pullman.Another 1-3+ inches.

BobE. said...

Thank you for taking the time from your weekend to keep us updated on the storms.

Sharon said...

I appreciate your dedication to your blog readers, Cliff! We'll keep watching and reading. Most important seems to be your readers erring on the side of safety.

Caddydan said...

Do you think this will turn into a structure crushing event like in 1996 with rain/freezing rain on top of heavy snow accumulations?

Seattle Tour Guide said...

Thank you for this, very helpful planning out a week where I am travelling. Got a 6:30am flight, sounds like I'll be in a nice little window after the first light juice and before the 2nd Lots of juice fronts.

Unknown said...

Click on them!

Brian said...

Click on them

Corie said...

7° in West Oly this morning...really hoping we dont get an ice storm like a few years ago...different than the 1996 event..
The different forecasts online are frustrating so I will stick with Cliff and also Shannon on KOMO.

Grant said...

You can click on the map and zoom in. Easy to read then!

Jaryd Ma said...

good job cliff

South Sound Guy said...

Cliff, after the eventual warm up any chance of a February weather postmorten analysis and a comparison with atmospheric conditions that resulted in the record cold spell of January 1950?

Colin Brinton said...

Thanks for the updates professor. I am enjoying following these.

Unknown said...

Cliff you don't mention high winds can we assume relatively calm wind conditions or did I miss that ?? thanks

Fresh Basil said...

Flake news!


I'll show myself out :)

Unknown said...

Dr Mass,
Just curious, when these computer models prove out wrong (like last weekend when there was less than a 50% of flurries and up here in Monroe, in Snohomish County we got 9"), do they get updated so that they are more accurate in the future? On the flip side, while everyone else got a lot of snow on Friday, we got less than 2".

thanks

Ron Wodaski said...

To those who said click on them, that turns out to be an interesting area. I normally read blogs, including Cliff’s, using a RSS feed reader. When I do that, clicking on the images gives me...the same image, at the same tiny size. I just checked, and when I read the blog directly, rather than in the reader, I get the larger, readable item. At least I know what’s going on now; I really did wonder about those tiny images!

High Pressure said...

Thank you for your many years of weather insights and forecasts. It goes without saying that when possible freezing rain is forecast, concern rises greatly. When you're able to, please provide your thoughts on the chances of an extended period of freezing vs. a short period of freezing rain over the next couple days and the probability of one or the other occurring depending on where you live.

SarahOrAlison said...

How soon would you know if "the low went farther south"?

RLL said...

I 'right click' and open in a new tab, then I can go back and forth post/map(s)

Erin Whittington said...

I can only imagine how exciting these snow events must be for you, Cliff. I remember how excited you were in meteorology class when it rained for 45+ days back in Fall of 2006.

Ann Stone said...

Up here in Kitsilano, right near Vancouver BC downtown, the "at most one inch" has been blown by we're at about 1.5 and counting. Quite heavy snow for the past hour or so...

M. Wallis said...

Cold blowing snow started @ 1pm (Sunday) at Mt Baker Ski Area. Drive home shall be interesting.

Goldogmom said...

Thanks for your great reports. Weather is a fickle friend ;-)

Scott8 said...

Looks like the low coming onshore more to the North of where some models had it coming. Vancouver BC is under a snowfall warning now.

Andy Pitts said...

Thank you Cliff.

Leafhopper said...

thank you Cliff, we've been pinned to your blog all weekend for updates! you really are a big help down on the farm!

Unknown said...

Snow is really coming down hard at the airport right now!

takirks said...

Y'know... I'd like to know when someone is going to take responsibility for convincing the various road departments on the West side of the state that they'd be safe to run down their snow and ice capability, due to not needing it because "AGW".

I can remember talking to someone on the Pierce County road crew about this very issue, a few years back--They were buying new trucks, and hadn't specified that they'd come with plow or gravel fitments because "AGW" meant they could economize by leaving them out.

Doesn't look too smart, this week, does it?

Another question is when someone at WSDOT is going to realize that they might need to relook at how they used to manage Snoqualmie and Stevens--When I was a kid, there were marshaling yards for staging trucks during storm events at North Bend and in Cle Elum, which were in routine use during bad weather years. If I understand where we're at today, those yards no longer exist, and there's no safe harbor for truckers and other travelers to go to when the passes are closed. This strikes me as... Unwise.

John said...

NWS 3:34PM zone forecast for Seattle tomorrow is awfully muddled/confusing.Talk about a "broad brush" forecast! I realize it's a very tough call,but maybe they can clean it up a bit.....


Bryan said...

Flurries started at 3, coming down fairly hard now in Shoreline.

Zoemama said...

4pm Sunday, dnow starting in Renton as predicted

Unknown said...

Carl Sagan of weather right here...

Unknown said...

Snow has started right at 4PM just as predicted here in the Maple Valley / Covington / Black Diamond area.

Chris said...

Amazing how microclimates are a factor. We always get a few more inches of snow at our place in Poulsbo

sewhidbey said...

Let's just hope it does not warm up quickly for a rain-on-snow event like the winter of 96/97.

Christina said...

Dr Mass,
I appreciate the updates and in particular your reminders that sometimes it’s just too close or uncertain to call. It’s up to the reader to decide how much TP and Oreo Thins must be stocked.

Jonathan Doe said...

Snow has been falling and accumulating for just over an hour in NW Bellingham. Temperature rose from a morning low of 15F a bit before 8AM to an afternoon high of 32F just after noon; 23F presently. Dew point is holding at 20F and precipitation intensity appears to be gradually increasing. Hoping for at least a couple inches by morning. The more the merrier!

Rabbits' Guy said...

It is 5 PM Sunday evening here at the Bow, WA weather reporting station. Light snow, getting colder, blowing a LOT. My trusty reporting rock is shielded from the wind but not the snow or cold and is cold and white. I don't know what its battery life is, nor where to plug a charger into it, so hopefully we'll get some decent sun soon. Interestingly, the local Safeway is out of celery!

Patrick said...

Light snow started falling in the Roosevelt neighborhood at 3:50 PM... 10 minutes early. Nice job with the forecast!

Jonathan Doe said...

What's with the persistent V-shaped rain shadow which tends to develop, expanding in east-west coverage from north to south over western Whatcom County? It's nearly always visible on radar during precipitation events and I've never heard any explanation for it.

Taryn Eng said...

Thank you for your very informative explanation of our weather and how the expectations are calculated. ��

dardevle said...

Hard winds in Issaquah from south. New snow 1” at best. Is this first storm scouring out the cold air ahead of tomorrow?

Pilot Mike said...

Assuming that foothill locations above 500’-1000’ elevation will be all snow regardless?

Unknown said...

Wish we had your expertise covering Oregon! I squint and make out what might be happening in PDX but.... Thanks!

[in the flesh] said...

Word.

Unknown said...

Located in Union at about 500' above Hood Canal and the Skokomish River Delta. Started snowing at 1 today and we've accumulated 6" plus and its coming down steadily at 6:21pm

Unknown said...

North of POULSBO, 4 inches since 3:30, pretty fluffy tho, holding at 30 degrees.

Unknown said...

Jonathan Doe,

I have noticed that too. I think it is not a rain shadow, but instead an area the radar cannot "see".

Tom Stone said...

Around 2-3 new in Phinney/Greenwood and coming down with a vengeance!

dardevle said...

Snowing super hard with hard south wind.

ryamkajr said...

More than 2 inches so far in Lake City Way/Maple Leaf. Been snowing since 4pm

Unknown said...

As a restoration carpenter and lifelong builder/contractor/tradesman I would like to point out that regional record snow also means maxing out construction minimum requirements for snow loads on roofs. Especially if you have flat roofs, sweep the snow off while you can (I just did). That winter mix that may occur can get absorbed into the fluffy stuff and gain weight rapidly, colapsing roofs... Also you could end up with ice or slush dams where water backs up and gets under shingles leading to leaks and interior damage...

Unknown said...

It's 7:20 here in Wedgwood and we've already received what looks to me to be 2-3 inches of snow, and more coming down. It seems that you might have under estimated Sunday's storm.

jen said...

It’s been snowing hard here in West Seattle since around 3:30p... lots of wind, but definitely much more than an inch here.

KBattgirl said...

I would like to see you try to predict weather in the Pacific NW. This is one of the most complicated areas to predict weather due to many factors. I find that the predictions here are far more accurate than most.

Ed Phippen said...

We’ve had 4” so far in Wallingford with another 2 hours to go.

craiger77 said...

I escaped my sister's on the Kitsap Peninsula today to drive back to the Oregon Coast where it is currently (7:30pm) 44 degrees with a strong south wind. She already has 4 inches of new snow starting from this afternoon so the prediction is a bit off there. Coming across the coast range on US 20 there was just rain and snow mixed an hour ago, but now the cams are showing lots of white. Happy to be out of the mess that is going to happen up there.

ryamkajr said...

coming up on 3.5 inches Lake City Way/maple Leaf. Although snow is tapering somewhat

7:47 pm

Unknown said...

Is there still a potential for lowland snow in the south tomorrow? I am around spanaway/eatonville area and if it is for sure all warm rain Monday night then I can just get ready for work... if there is a chance for more snow then I will be more cautious.
thanks

Carly, The Wine Princess of Washington said...

Im in montlake and it dumped for 2 hours

This past week has been bananas!

MAC in Bellingham said...

3 to 4 hours of light to moderate snow here in Bellingham near the airport. About 2" on the ground. It appears to have stopped, at least for a while, but radar shows more to the west. Temperature dropped to 23F. So far, pretty much as forecast.

NWS still not forecasting much snow this far north.

See what tonight and tomorrow brings.

Joseph Ratliff said...

In Olympia / Lacey, tonight's computer forecast missed the mark on the wind BIG TIME.

Forecast 11-16 gusting to 22mph from the South. Peak wind 32 gusting to 39mph from the South. Several gusts over 30 - 35mph. Power went out for 2 hours then came back on.

That computer forecast needs work, and a lot of it. When it misses, it misses by a long margin (this has happened several times for wind, snow, and rain - temp not so much).

ljb said...

About three to four inches here in Ravenna this evening.

David B. said...

Tonight's snow band gave me 4.9" here on Bainbridge Island. Most of that fell in two hours; my peak hourly rate was 2.6"/hour! This storm definitely exceeded expectations. And the convergence zone may sag south and drop another inch or two!

Now on to the "main event." I only need 3.6" more snow to top 20" for the month.

Unknown said...

At least 3 inches of new snow near three lakes area in Snohomish

Pizano said...

Cle Elum area has been getting snow all day. What's wild is as much as it has snowed throughout the day the accumulation isn't as much as I thought there would be. With that said though we have had low to medium as well. The snow is very dry.

Unknown said...

North Bend is NUKING!!! This is so awesome.

Unknown said...

Got at least five inches tonight near Evergreen University in Olympia. Light and fluffy at least...

Mike P. said...

West Oly 5" between 3-8PM. Lots of wind accompanied the snow, but calm and clearing now. Temps steady around 30. Over 12" on the ground after today.

embedded engineer said...

At 9:16 the snow has stopped, we received 2". Shoreline (just north of Seattle).

gnolan said...

I would like to echo what Ron Wodaski posted: the (typically graph axis) numbers on the figures you post are pretty hard to read. If I copy the image into graphic viewing software the resolution is poor. Please post larger images that contain quantitative data or provide links.

Andy DeCeunynck said...

Tonight's snow was not quite a minor event. 3 new inches on Beacon Hill with most of it falling between 6-8PM. Almost all arterials in SE Seattle (Rainier Ave S being the only exception) were solid ice around 8:30. Luckily, my AWD handled things well but I saw at least 3 cars stuck. When I got home at 9PM, I noticed that the southerly winds felt relatively warm compared to the last few nights and lo and behold, it was 36° at KBFI.