February 23, 2011

6 AM NOWCAST: Seattle Commute In Will Be Fine

Here is the story at 6 AM. The commute for Seattle and to its west should be uneventful. The winds aloft are still westerly aloft that we are in the rainshadow of the Olympics and that should not change much before 8 AM. As normal for rainshadow, precipitation picks up in the eastern suburbs east of Lake Sammamish. Snow showers are moving into the region, but as seen in the radar most of the action is north of Everett and south of Bellingham. So Whidbey Island, the San Juans, and the northern Olympics are seeing snow showers now, some occasionally heavy.

In fact, you will notice the heaviest precipitation is over the eastern Strait and westward and that is probably due to the convergence of modest NE flow coming out of the Fraser and southerly wind coming up the Sound and westerly wind moving eastward in the Strait (see map below). Such low level convergence forces upward motion. WATCH THAT BOUNDARY--that is where the big action will be today. Go south of McChord and there are snow showers moving through the Chehalis Gap. Moderate to heavy snow on the western slopes of the Cascades and foothills.

So bottom line for Seattle commuters...you will have no problem getting into work. Temperatures are above freezing and road surfaces are wet. Looking at the satellite pictures (see below) I am not impressed with what is coming in from offshore. Not much cooling of the cloud tops (such cooling means deepening of the clouds and intensification). The models indicate that during the day the flow approaching the region will weaken and turn more southerly....that will open Seattle to snow showers, and as the low moves south, northerly flow will push southward. But not yet.


Last night the NWS was going for a hard freeze of this stuff later today during the commute home. Looking at the situation now I believe that is highly unlikely. Temperatures will remain at or slightly above freezing during the day. Major urban roads should be ok, particularly since many DOT's applied deicers. The only failure mode would be if the snow rate gets SO large that we get a slippery slush layer after the deicers get diluted.

Reminder...my talk at Ivar's Mukilteo has been delayed to March 9 due to snow forecast. It will not be good if it doesn't snow!

40 comments:

  1. Thanks Cliff! My kids are peering out the window with great hope and anticipation!

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  2. Can you please define "not impressed"? Does that mean that things are going to be ugly or uneventful in Seattle? Thanks!

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  3. Woke up at 4:30 AM from the sound of hail/grapple pounding my roof. Snow started about 5 AM. Snowing hard now, with about a half inch accumulation so far.

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  4. I thought the winter storm warning was a bit much here in Bellingham by looking at the snowcast.. I would have gone with a snow advisory. We will see who wins out. The dryer air from the outflow, which is picking up, or the onshore dude. But I don't have thousands of people watching my forecast including emergency services. I guess you want them to plan for the worst.

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  5. Thanks Cliff, your un-hyped information is, as always, helpful in making commuting decisions.

    Bonnie
    Haller Lake 34.7F, .5 accumulation
    no precip at this time

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  6. Winter wonderland in Skagit County. ~1 inch on the ground and growing. Schools cancelled on Whidbey and Camano. It's like walking around in a snowglobe :)

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  7. FIne, we can get to work --- can we get back home this evening?

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  8. In Laurelhurst at 7:30am, and there's no snow in sky or on ground.

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  9. In western Skagit County it is snowing at three inches an hour. As of 7:20 a.m. we have five inches of snow!

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  10. 7:40 am: 1" or a bit more on the ground on the west side of San Juan Island, and still coming down steadily.

    Yesterday, Cliff, we were threatened with very high winds with gusts to 60 coming out of the Frazier Valley. It looks as though this forecast has been reduced, but do you have a current idea how bad we should expect the winds up here to get?

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  11. east woodinville about 3/8 inch on ground and snowing steadily

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  12. Snowing moderately heavy here on Sinclair Island. Started around 7am. Temperature hovering around the freezing mark. Snow sticking everywhere. The wind is brisk from the SE which indicates to me a surface low has formed just to the west or northwest. Also portends a prolonged period of snow for the islands depending on how long this low lingers over us and if it intensifies at all. But that would account for milder conditions in the Seattle area for the time being.

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  13. Heavy snow flurry in Port Angeles,
    http://twitpic.com/42xuo1

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  14. Any thoughts about being able to make it tomorrow (Thursday) from Seattle to Seabeck on the Hood Canal? I'm supposed to lead a workshop there and people are flying in from out of town. Don't know what to advise!!!

    Andrea

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  15. Snowing here 3 miles NNE of Monroe at 400', with varied intensity. Just under 1" new this morning so far on top of the couple of inches we got yesterday.

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  16. No trouble commuting unless you live in one of the outlying areas, east of Lake Sammamish where as you said "the precepitation picks up". And come on out and you will find that there are a whole lot of us, and many of us commute to Seattle! And people north and south commute to Seattle as well. Saying that there will be no problem commuting to Seattle is really a travesty, and potentially a dangerous one, if employers and colleges rely on that mis-information.

    The Seattle commute isn't just about Seattle....something that Seattle-centric weather people love to forget. I so wish that more weather people lived in the suburbs....

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  17. So my Seattle Lowland Snow Model proves correct once again:

    http://twitpic.com/42m7gk/full

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  18. cliff - it looks as if there may be a good 4-5 inches around Silverdale/Bremerton area per WRF-GFS morning runs as the band/arctic front moves south. Are the models overplaying this?

    Has timing on this slowed down? It appears so! Look forward to your next update :)

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  19. Well when LWSD cancelled school this morning at 6:15 with nary a flake of snow on the ground, I thought for sure things were a "go" on the eastside. But your words make me think they are overreacting. It is even early release day so the busses would have been done by 2:30.

    By the way, we have had graupel - a word I didn't know until yesterday. My kids had graupel with maple syrup for dessert last night.

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  20. 8:30 am West Seattle. Upper Fauntleroy. 36.3 degrees on my back porch. Blue skies, puffy white & gray clouds, windy & even a little sunshine mixed in.

    Definitely NOT snowing. :-(

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  21. Not snowing in Ellensburg yet, if Snoqualmie Pass can stay open long enough for one to get through...

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  22. Looking at the last couple of hours of the radar loop, the snow is having real trouble getting into Whatcom co. It seems like the outflow is already winning, which makes me think B'ham wont get much snow, and the boundary front will set up south of here, probably over the same place that has had the convergence zone. If that happens, my guess is that somewhere ins Skagit or Snohomish co. could get well over a foot, when all is said and done.

    Pretty impressive snowfall for late Feb!

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  23. No Snow on Mercer Island at 8:53 AM

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  24. @TVN...LWSD covers such a wide range of terrain. We live east of Redmond and already have enough snow that getting to and from school would have been dicey. I bet parts of Sammamish are even harder hit. Pity there's no way for the school district to HALF cancel!

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  25. On the west side of San Juan Island at 475' we have 5-1/4" at 9:00 a.m., and it's still snowing lightly. We had less than 1/2" at midnight last night, and i'd estimate that at least a third of what's on the ground now fell after 6:30 a.m.

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  26. Downtown Redmond area and no snow.

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  27. Sunshine over Lake Union at 9:20 a.m. What do the models show now?

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  28. Sunshine over Lake Union now. What do the models show at this point?

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  29. At 560 feet, about 5 miles east of Lake Stevens we have steady light now and about 5-6" total.

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  30. Puget Sound gets a Mesoscale Discussion 120 from the Storm Prediction Center, Norman OK. That's an oddity.

    Is the mesolow a lee effect or a convergence effect?

    http://www.spc.noaa.gov/products/md/md0120.html

    AREAS AFFECTED...PORTIONS OF NWRN WA INVOF THE PUGET SOUND

    CONCERNING...HEAVY SNOW

    VALID 231630Z - 232030Z

    SNOWFALL RATES REACHING OR EXCEEDING 1" PER HOUR LOCALLY CAN BE EXPECTED INTO THIS AFTERNOON.

    LATEST RADAR IMAGERY SHOWS A CONCENTRATED AREA OF HEAVIER PRECIPITATION OVER ERN PORTIONS OF THE STRAIT OF JUAN DE FUCA AND FAR NRN PORTIONS OF PUGET SOUND -- WITH IR LOOP CONFIRMING THE INCREASING ASCENT WITH SUBSTANTIAL CLOUD-TOP COOLING.

    THE ASCENT IS BEING FOCUSED ON THE MESOSCALE BY A VERY SMALL LOW IN ERN PORTIONS OF THE STRAIT...WITH A CLEAR CIRCULATION EVIDENT IN LATEST SURFACE MESOANALYSIS ACROSS THIS AREA. AS THE LARGER-SCALE UPPER TROUGH SHIFTS SLOWLY SWD/SSEWD...A CORRESPONDING SWD SHIFT OF THIS MESOLOW APPEARS POSSIBLE -- WHICH SHOULD ALLOW HEAVIER SNOWFALL RATES TO SPREAD ACROSS NRN AND INTO CENTRAL PORTIONS OF THE PUGET SOUND OVER THE NEXT FEW HOURS. WHILE ATTM IT APPEARS THAT SNOW MAY REMAIN NORTH OF DOWNTOWN SEATTLE OVER THE NEXT FEW HOURS...STEADIER SNOWFALL COULD POSSIBLY REACH SEATTLE THIS AFTERNOON.

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  31. @Thompsonized -- I live in Eburg too. Starting to get a few fat flakes now (outside of town to the west @ 9:40).

    Good thing I haven't had to go over Snoqualmie Pass in the past few days. When the Pass isn't closed, chains have been required (and I don't have any)!!

    I'm hoping the forecast remains good for the weekend, because I *do* have to drive to Bellevue on Saturday morning for a conference.

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  32. 9:40AM Olympia / Budd Inlet:
    At 7:30AM a snow squall came through, giant beautiful flakes floated down for about 20 min and left ~ 1/2" on the ground. 33.1F

    Then mostly sunny for the next two hours.

    At ~9:30AM it looks like a repeat--much darker and moderate snowfall. Temp: 34.3F
    Streets bare below 100' elev.

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  33. My comment last hour has been confirmed by the latest forecast discussion. Sounds like it will be too cold and dry for W Whatcom co. to get much from this storm.

    All the fun will be south of here - shame.

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  34. At 10:00, 3" plus on ground on west side of San Juan Island. Steady snowfall ended about 20 minutes ago, now just light flurries, at least for the time being, but radar shows more on the way.

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  35. NWS this morning is saying 3-7 inches for Everett area today..and addtional 1-6 inches tonight. so 4-13 inches today and tonight

    Seattle-Tacoma 1-2 inches through the day and up to 6 additional inches tonight.

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  36. Are there any other cams out there like the Dale Ireland cam? It would be fun to have several of those with amazing views like that sprinkled around the northwest.

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  37. Just started snowing in the Auburn valley, right by the "stupor mall." Not sticking yet, though - just little flakes blowing around.

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  38. 5+" at 60' elevation here in Anacortes near Guemes Channel. All in the last six hours, bare ground at 5 AM.

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  39. 1:40pm, still not a single flake of snow in West Seattle (Fauntleroy). Sunny. Cold. Breezy. Darn it. I was really looking forward to this Big Snow Event.

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  40. Cliff: It's so great to flow through your earlier NowCast and how you make living here amid all this fascinating weather even more alive & special...as snow wave after wave has stormed over, between & around us this past afternoon & into early evening. Now mostly afterwards we're over here in the foothills south of Port Angeles up against the Olympic Mts (at ~700 ft elev) at ~2115 hrs with a good 6 inches of snow mounting on the level. But you couldn't x-c ski (pleasurably) over our field on it, since while beautiful it was still about as sticky-wet & heavy new-fallen stuff as I've ever seen (& shovelled) in my 40 yrs. living here. Carry on!

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