Wednesday, December 17, 2008

Snow Situation Today


noon update: The forecast needs an update. Some parts have worked out well...the rainshadow appeared as predicted and snow--heavy in places--occurred to the north and south of it (mainly north). So what about the CZ snow? It is occurring...but is further north the predicted...but probably will move southward later. Look at the latest radar...you see the heavy shower from roughly Port Townsend that extend to the NE...thats the cz showers...and some areas are getting substantial snowfalls in it. There is heavy snow north of Everett...with lots of places getting 3-6 inches. There appears to have been more troughing (lowering of pressure) offshore and that has resulted in the winds aloft being more southwesterly than expected..the result...the cz being further north. The latest computer models suggest that later this afternoon and evening the winds will turn more westerly and the CZ will move southward and finally give some snow over central PS. I know some people are disappointed and some school districts cancelled classes...


The weather system from the north started bringing light precipitation (generally snow away from the coast) to the region after midnight--with the precipitation extending over the area by 5 AM (see radar). As predicted by the high resolution models there is a profound snow shadow extending from the Olympics to Seattle....the radar image is really quite amazing. The borders of the rainshadow have moved a bit over the past few hours...but this feature is shielding central Puget Sound. Away from the shadow, light to occasionally moderate snow is fall...from Snohomish County up to Bellingham and the far eastern suburbs of Seattle where upslope on the Cascades brings back the snow. There is also snow south of the rainshadow...particularly south of Tacoma.

With the system, the winds aloft have switched to southerly or southwesterly and temps have increased aloft...even at the surface many temperatures are near or just below freezing. Along the coast it is warm enough for rain.

Now this is a snow event with two acts. We are in the first one now, and light snow will continue in the non-snow shadowed areas through commute time, with several inches possible.
Act II will start between commute time and 1 PM: convergence zone snow. The latest computer models suggest a band of enhanced CZ snow will form north of Seattle --probably centered in Snohomish County-and then move slowly southward during the afternoon and early evening before dissipating later tonight. In the CZ far heavier snow amounts are possible...4-8 inches are not unreasonable. See the attached model snow forecast for the 24-h ending 4 AM tomorrow. And the mountains are getting a very good dump, with at least of foot.
There is a long history of convergence zone snows in the area...one of the most memorable being the event of Dec 18 1990 when Seattle had a foot and virtually nothing fell at Everett and Sea-Tac airport (my book has a section on this storm). That cz snow was completely unforecast...we didn't have the high resolution models we use today.
Tomorrow things should dry out..but then ANOTHER surge of cold air and strong NE winds out the Fraser River valley should develop. And yes, the weekend snow storm is still out there.

41 comments:

Anonymous said...

Cliff, Thanks for the frequent updates. I'm impressed when comparing the model graphic to the radar.

Anonymous said...

here in chehalis, its weird, if the system is coming out of the north the wind is fierce out of the south

Cliff Mass Weather Blog said...

Thats right...are is flowing towards low pressure...cliff

Anonymous said...

Cliff,

We're getting a good amount of snow south of the shadow here in Olympia. With the strong SSW winds, will 200-400' elevation be enough to overcome the predicted warming into the upper 30s and keep everything all snow?

Lindsey said...

Very interesting re the still-forecasted PSCZ. I guess I'll believe it when I see it. Frankly, this definitely does not seem to be that impressive a storm yet almost anywhere in western WA. On the radar, the moisture appears very broken, rather than the solid swath of precipitation in most incoming storms. Also wondering just how much it will warm up Seattle to S. Snohomish Co. before any snow happens.

fjblau said...

Good Morning weather nuts!!

Out here in Sammamish we're looking at 35 degrees and no snow yet at 9AM...

Winds are all <10MPH from the SE at the moment....

Scott K said...

Well, here in lake stevens we woke up with another 2 to 3 inches on the ground. Snow stopped around 6 or 6:30...but just started up again as of 8:45. Roads are a complete mess, several accidents around my neighborhood already (basically everything around here is a hill). Neighbor almost slid into the lake after sliding across 2 lanes of traffic while coming down a hill.

I'm fairly confident we'll see another several inches by the afternoon. Yes, it's warmed up to about 32, but that won't last.

Anonymous said...

So glad to have found your blog! Your KUOW reports are huge in my family, and now we're excited to know where to find you online.

It's looking like the wishes of every child on Bainbridge are going to be denied, or answered only lightly - Our island seems to be in the one little area of no/light snowfall between the peninsula and Seattle. The sky looks like snow, but the map says NO.

Brad said...

A few flakes in Mountlake Terrace this a.m. Kids are sitting on their sleds waiting for the CZ. I keep humming "I'm being followed by a snow shadow." Thanks for the great blog, Cliff.

theartist said...

Yes, thus far "bust" would describe the storm very well. The "snow shadow" is BIG. Even in Mukilteo we're getting zilch.

Depending on the convergence zone to save the snow forecast is dubious, but hey, so far we are 0-2 in snow, perhaps we'll bring our average up to a respectable .333.

I will agree with the other poster that the precipitation in this "storm" is sad. It's broken up and spotty, looks more like isolated showers than any real system.

If I had to look back on this event in a few years I would think, "yeah, it was cold there for a week" and that would be it. Nothing else about this is memorable and I can think of a LOT of other snows where it was warmer that were much more memorable, 1990, 1993, 1996, 2000, 2006, and the snows last winter.

Heck, our April 2008 snow was more memorable than this. ;)

still time to recover, but it seems that weather goes in trends, and it's been cold but wimpy all week.

Lindsey said...

Given that the NWS is in line with Cliff on the idea of CZ forming later today, I'll hold out hope -- though it sounds like, even on this, it will happen later than what Cliff was saying. Basically, I think the precipitation shadow effect was more significant than anticipated (nearly up to Everett rather than just the immediate Seattle area), and so those areas will just end up with less snow than had been forecast.

Looking at the current radar, it looks like MAYBE some shots of snow are aiming for the snow-starved areas, but often those things fizzle out.

Cliff Mass Weather Blog said...

see the main page....for comment

Doug V said...

I'm at an elevation of 515' right smack in the heart of the PSCZ (South Snohomish County) and it's not snowing, hasn't snowed, and doesn't look like it will snow.

How does my observations of the weather in my backyard comport with forecasts of up to 8" in the PSCZ?

Me thinks the Seattle weather establishment got fooled by a fickle Mother Nature on this one.

Maybe she'll prove me wrong and the forecasters right, but as of noon today this snow event is a bust.

Anonymous said...

Cool blog! thanks for explaining it, very interesting. And amazing pics!

Anonymous said...

Re: Doug V,

If you are in South Snohomish County then you are currently south of the PSCZ (as of Noon). Remember the PSCZ is not a static area... depending on the wind direction it can form in differnet areas. Currently, as Cliff's Noon update explains, it is well north of your stated location. As the low moves away, the winds coming toward the Olympics will change direction and hence the position of the PSCZ will change (i.e. from SWerly to Westerly will bring the PSCZ more south).

Lindsey said...

Thanks, Cliff (sniff, sniff . . . ). Obviously we all see once again how inexact the science of weather forecasting is.

I can only hope that these latest computer models are correct because the previous ones sure weren't!

Moon Valley said...

I'm in North Bend right up against Mt Si and no snow. Temp is 39 and raining. Didn't expect the shadow to extend this far east. It was 19 degrees last night around 8PM then started warming up. Really ramped up above freezing when the south wind started blowing. Looks like some precip is moving up from the south due to the far north PSCZ, but it is too warm for snow. Kids are really bummed.

Anonymous said...

"Act II will start between commute time and 1 PM"

Do you mean 11 pm? 10pm?

wholeclothdesigns said...

We've had very heavy snow in Olympia all day. I measured about 3 1/2" an hour or two ago and I live at an elevation of 50 ft at the most. It's amazing how different the weather can be between Seattle and Oly.
Thanks for your blog and for your weekly KUOW appearance!

Lindsey said...

I don't wish to get anyone's (including my!) hopes up, but looking at the radar, there sure appears to be a little SE progression of that mass of moisture to the northwest of many of us.

Anonymous said...

I'm a bit confused by your interchanging usage of rain and snow shadow -- don't they essentially mean the same thing, an area where no precip occurs due to a preceding object squeezing all the water out? If you're in a snowshadow and it rains, can you really say you're in any shadow at all? That sounds to me more like you aren't in a shadow, you're just in an area that's too warm for snow.

Anonymous said...

I noticed that the arctic air outflow in Bellingham has just started up again in the past hour or so.Where is the surface low now, exactly? It looks like it`s near the southern tip of Vancouver Island.If this is correct, and the low continues to move E or SE shortly, shouldn`t the winds begin to turn more northerly and drive the cz southward in just the next few hours?

Lindsey said...

Good catch on the northerly outflow, Anonymous. I like your reasoning and I hope you're right.

Anonymous said...

It sure is snowing hard in Olympia, even at 0 ft. It has been snowing for more than 8 hours, and has really started to pick up in the last few hours. According to NOAA, it was 32 degrees at 1:54pm. I hope it stays snow!

Cliff Mass Weather Blog said...

yea of little faith in convergence zone snow...be prepared to meet you white, fluffy maker!

Anonymous said...

The CZ has made a pretty good run over the last hour, just now getting to the edge of everett. The million dollar question now is how "low" (south) does it go.

Michael said...

Sun just came out here in North Seattle ( Ravenna )

Brad said...

Get ready. Pretty dark looking in Mountlake Terrace

Michael said...

Yep, now its darker than the heart of Cheney

Mike in MLT said...

330pm--nice Graupel shower with some snow in MLT! Would really like to get an hour or two of thundersnow. The kids are very excited...

Scott K said...

Here in lake Stevens it started snowing moderately again about 40 minutes ago. Started out as a very wet snow, possibly mixed, but now it's 100% snow and sticking quick.

However, we lost about 2 inches of snow during the daytime melt, makes for a very slushy road...and now it's going to freeze with fresh snow on top of it. What a horrible combo for driving, but at least that convergence zone seems to have made its way here!

Scott K said...

Scratch that...it's snow VERY hard right now. This must definitely be the convergence zone saying hello to us finally. :)

Matt said...

I'm sitting at my desk in Fremont, looking out over the Fremont Bridge. Clouds are rapidly moving to the NE. No snow, not even rain. Everyone in the office is bummed. Hope the CZ moves further south! But I'm not holding my breath.

natchrl8r said...

Up here in Bellingham we had snow sprinkles deposited overnight. By 9:30 we had regular snow showers, by 11:30 was snowing heavy large flakes and cold enough for powder again at noon. Just stopped a little while ago. (About 4pm) The sun is even showing a little color on the horizon as I write to make for a perfect snow day. No disappointment at all here! The forecasters seemed to have it right, at least in the warnings and discussions.

Anonymous said...

is the moisture that is moving south rotating clockwise?

signalius said...

Watching the largely conflicting weather reports on numerous tv stations today, the only thing that was consistant was the apparent disdain for the white stuff, suggesting it's only a boon for schoolchildren. I resent this anti-snow rhetoric from these over-the-hill party poopers! It's fun! Snow happens so rarely here it should be a welcome departure from the dull pace of normal life. At least the networks should be thankful for the increased ratings the threat of snow must generate! More. Snow. Now.

wholeclothdesigns said...

We've had a full day of sledding and snowman building in Olympia. All day long kids and parents have been walking up to the neighborhood hill for sledding.

Snow fall has basically stopped since 5 PM, but maybe we'll get a little more later on from the cz?

SeaRod said...

I know that it is ostensibly a positive thing that Seattle has been spared the type of pounding that Stanwood, Marysville and Everett have received. Traffic has not halted in its tracks (here in the city), people are not slipping, falling, and breaking things, and the city has not had to expend resources removing snow. However, here on First Hill, I can't help feeling cheated. Not that I need a foot, 2 or 3 inches would do nicely. But, we never seem to be on the receiving end of these "snow storms." Thank god we're talking about the weather... otherwise I might begin to suspect a conspiracy.

Anonymous said...

Snohomish town folklore says the snow would get to be as "high as a squaw" .... maybe this is the winter for something like that again. It's been dumping steadily for about 4 hours now.

Anonymous said...

Signalius, why do you talk about snow being fun and dislike all the anti-snow talk and disdain for it (all which I wholeheartedly agree with), and then talk about the snow as a "threat"? It doesn't make any sense to me. If snow is fun, which is definitely is, why does it get a bad term like "threat"?

JewelyaZ said...

Cliff,

Thanks for an outstanding blog. I really enjoy your weather predictions and following the complex weather patterns around here. I moved to the area ten years ago from North Carolina and I'm not bored yet -- though I do miss me a big ole hurricane once in a while! ;-)

Here's hoping that the giant box with my name on it under the Christmas tree is a Davis weather station with all the gizmos... we live about 180 feet directly uphill west of Lake Sammamish (about .3 miles from the water's edge) and we get some weird "lake effect" snow where we will have way more snow than our neighbors just three or four blocks west. I'd love to be able to quantify that difference over time in a more exact way and will put my new weather station on the web if in fact that's what that big box is.

Anyway, good work and thanks for bringing the science to those of us who are intensely interested "laypeople".