November 21, 2010

Sunday AM Update

There is a very weak upper level disturbance passing over us this morning and will be through by noon. It has enhanced some clouds and is producing light snow showers. That is all it is going to do over the lowlands north of Seattle. The amounts will increase as you approach the foothills due terrain-induced upslope flow. South of Seattle there is the possibility of perhaps an inch or two. Lets be explicit.

Here is the latest high-res model output for the 24-h snow fallending 4 AM tomorrow. Seattle is being protected by Olympic rainshadowing---farther south the rainshadowing weakens..and thus there is light snow. Thus, the south sound will get some light snow as will foothills locations.

Tomorrow a stronger disturbance will approach, it will increase the flow out of the Fraser and other gaps, and deepen the cold flow so that some will go over the mountains (see graphic). The models indicate that the snow will head south of us (see graphic). But if the models are wrong...you know what can happen. This is close.

38 comments:

  1. Are you sure? because it's coming down in big fat flakes and sticking to everything but the roads (so far) up on Tolt Hill near Carnation.

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  2. We have about 2in of snow this morning in Enumclaw and it's still snowing!

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  3. .5 inch skiff in Edgewood! Some light flurries still.

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  4. just a sprinkle in Redmond at sunrise

    at work in Canyon Park / Bothell

    nothing

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  5. What a nice Sunday surprise! Woke to light, fluffy flakes, and a dusting this Sunday AM, near SE Auburn with temp at 32. Looking at the models last night I did not see this. Really hoping the Low forms off the North Coast tomorrow and the models are to far South!!! Should be a fun next 48hrs. watching radar and cams! Note: At 9:20am, radar showing a large band of precip. moving down the the Strait and a band forming off Edmonds.

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  6. It has been lightly snowing in Maple Valley all morning.

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  7. 10:15 - snow started in W. Shoreline. Nothing sticking here so far.

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  8. It's blowing little and a little bigger snow flakes here in north Seattle (Haller Lake).

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  9. Just started snowing in Hoquiam, at about 13' elevation...

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  10. Very light snow and breezy near the Ballard Locks.

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  11. Flurries up in Shoreline. Looks nicer than rain!

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  12. Just stopped snowing around Lake Tapps. We have about an inch so far. My girls and I made a good size snowman this morning. Currently 36 degrees here.

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  13. Snowing very lightly on the north side of Queen Anne Hill.

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  14. Well, I don't call this snow exactly (200 foot elevation near Woodland Park) but a few fat flakes are falling and my daughter is jazzed. NWS seems to think there could be some snow, so???

    I am a snow fanatic so I hope so!

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  15. So, Cliff? That's.. what. Three blogs wrong now? One last week where you stated: "Forget lowland snow this weekend." Two: "Saturday and Sunday are going to be pretty dull around here." Three: "Forget most of western washington for snow." Four: "My conclusion, if the models are correct, the central Puget Sound Region, including Seattle, will get little if any snow."

    Three strikes your out at the ol' baaall game!

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  16. Started snowing at noon on Capitol Hill at about 300 feet.

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  17. Lake Stevens this morning woke up to a light dusting, it started snowing again for a couple hours, stuck on the ground for a bit then warmed up. Now it's just light snowing, but the snow on the ground is gone.

    Cliff, I know you said it's suppose to dry out tonight/tomorrow, but the 12pm Winter Weather Advisory(just updated now) from National Weather Service calls for 1 to 2 inches of snow in the seattle area, especially north and east of seattle. Yet, everywhere else I read says the snow is only going to be south, olympia, orgeon, etc.

    Why does the National Weather Service winter advisory differ so much from all of the other forecasts so far?

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  18. Spoke too soon. Ballard snow is gone. You're right again. Damn. I want CHAOS!

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  19. Been snowing in Aberdeen for about an hour and a half, with about an inch and a half accumulation. Will it melt before night falls?

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  20. Cliff- It seems as if the models always under guess the amount of snow with an arctic air mass.

    Lots of light snow around and the next much bigger wave seems to be moving onshore now.

    Im betting for snow in Seattle on monday.

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  21. This is just my gut feeling, no science, but I'd say the models are wrong.

    Of course, part of my gut feeling stems from the fact that this fall when forecasters predict rain, it was clear and visa versa.

    The snow is coming down in buckets in Sammamish. The clouds are doing an awesome job of dropping the moisture they weren't supposed to have. Thankfully, it's warm enough that it's only collecting on the trees so far.

    I think in this part of the country where people aren't used to driving in snow, it's more responsible to err on the side of over-predicting snow than on underpredicting. When you underpredict, people who really shouldn't go out, do go out, and we have a meess.

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  22. Not a single flake to be found in Mount Vernon area. Sigh...

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  23. Light-to-moderate snow here in Tacoma.

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  24. We woke up to a dusting of snow in Olympia that soon melted. It's been snowing here now since before noon but so far it isn't sticking.

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  25. According to the radar the snow is coming back from the southwest, moving northeast at a decent pace. Some places are getting a rain/snow mix but it looks like most are getting snow. Now it just depends on what the temperatures do this afternoon.

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  26. It's still snowing lightly here in Ballard at 2:15pm but it is not sticking. Very pretty though. Once again wishing I was closer to the foothills!

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  27. Cliff,

    Just wanted to reinforce that you were right in your blogs this weekend. The models and the snow charts you posted were right on.

    Simply amazing the progress being made. Thanks for all the updates too!

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  28. Been snowing here in Lacey since noon (lightly).

    no - little accumulation...but this Winter Advisory just went up:

    Winter Weather Advisory
    URGENT - WINTER WEATHER MESSAGE
    NATIONAL WEATHER SERVICE SEATTLE WA
    1157 AM PST SUN NOV 21 2010

    ...A WINTER WEATHER ADVISORY IS IN EFFECT THROUGH MONDAY EVENING...

    WAZ504-512-516-517-220400-
    /O.NEW.KSEW.WW.Y.0016.101121T1957Z-101123T0700Z/
    SOUTHWEST INTERIOR-LOWER CHEHALIS VALLEY AREA-NORTH COAST-
    CENTRAL COAST-
    1157 AM PST SUN NOV 21 2010

    ...A WINTER WEATHER ADVISORY IS IN EFFECT THROUGH MONDAY EVENING...

    THE NATIONAL WEATHER SERVICE IN SEATTLE HAS ISSUED A WINTER
    WEATHER ADVISORY FOR SNOW...INCREASING THROUGH MONDAY.

    * AFFECTED LOCATIONS...INCLUDE THE I-5 CORRIDOR FROM OLYMPIA
    THROUGH CHEHALIS.


    * ACCUMULATIONS...SNOW ACCUMULATIONS WILL BE UP TO 1 OR 2 INCHES
    TODAY. A MORE GENERAL SNOWFALL OF 1 TO 3 INCHES IS EXPECTED
    MONDAY...WITH LOCAL ACCUMULATION OF 4 INCHES ON THE HILLS AND
    EAST OF INTERSTATE 5.

    * WIND...BREEZY NORTHERLY WINDS OF 15 TO 25 MPH WILL DEVELOP
    MONDAY AFTERNOON OR EVENING WITH FALLING TEMPERATURES INTO THE
    20S...CAUSING WIND CHILLS IN THE TEENS.


    PRECAUTIONARY/PREPAREDNESS ACTIONS...

    A WINTER WEATHER ADVISORY MEANS THAT WINTER WEATHER WILL CAUSE
    TRAVEL DIFFICULTIES. BE PREPARED FOR SLIPPERY ROADS AND LIMITED
    VISIBILITIES...AND USE CAUTION WHILE DRIVING. CARRY WARM CLOTHES
    IF DRIVING IN CASE OF TRAVEL DELAYS.

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  29. It's been snowing steadily in Aberdeen since 1030 am, and accumulating since noonish...a couple inches, I'd say! Keep it coming!

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  30. Snowing here on the UW campus, hard at times. Not much is sticking, but if it keeps it up, who knows?

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  31. The temp is falling in Olympia and so is the snow. It is sticking now on the grass. I just put on the new Pink Martini Christmas CD and I'm going to have an eggnog latte and enjoy the scene.

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  32. Just over 2 inches in Eatonville...started about 10:00 am. I'm guessing school will be on a 2-hour delay or closed all together since they are calling for more snow and wind tomorrow.

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  33. Dumpin pretty good here in Enumclaw. Have about 2 inches so far in town......keep it comin!!!!

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  34. The 12Z Sun 21 Nov WRF-GFS run is showing the short wave trough moving with uplift this evening and tonight over Puget Sound (and the rest of Western WA).

    http://www.atmos.washington.edu/mm5rt/data/2010112112/images_d2/500vor.15.0000.gif

    More interestingly the 12Z Sun 21 Nov WRF-GFS it now has a closed upper level low sweeping over Western WA on Monday. So from about 7pm Sun through 7am Tues there is vorticity (and uplife) aloft first from the trough then from the low.

    http://www.atmos.washington.edu/mm5rt/data/2010112112/images_d2/500vor.36.0000.gif

    This looks similar to, though less intense than, the NAM model prognostication n the previous "Uncertainty" blog entry.

    But ... is there any water to precip with that uplift?

    The WRF-GFS snow prediction keeps the metro area clear of snow. The models precip will fall as rain from 10am to 4pm then dry up (that's what we see now ... wet snow/rain). And that's it. No more precip this evening or tonight or Monday in the Puget Sound.

    The precip is trailing off on Capitol Hill at 3:30pm.

    What do the NWS forecasters know that the mesoscale models aren't getting? Is the model right or do the forecasters have some extra skill?

    The next AFD should be interesting. It's not up as a type this.

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  35. Before people get too worked up about "the snow" and "the failure of the forecast" take a look at Rainwatch

    Click for Rainwatch 24 hour rain accumulation in Western WA

    Click for Rainwatch 24 hour rain accumulation in the Puget Sound

    Over most of the region (and especially over the the Metro area) the 24 hour accumulation is less than 0.1". There are some areas above 0.1" in the South Sound. There are also a handful of hotspots (and I'm not sure if they're not artifacts) north of Orcas Island and over Mt Baker(?) with with red intensities (wet snow? intense snow showers?). Wet snow has a larger radar cross section than rain drops so even these plots might over-estimate the total precip.

    Remember an 1" is less than 0.1" rain so a little rain as snow goes a long way.

    Looking at the precip rate you can see the rate (aside from a few heavier embedded showers) over most of the Puget Sound lowlands in 15dBz or less with showers < 25dBz. If this were rain you wouldn't notice it (a light drizzle).

    The precip band is SE to NW across the South Sound just clipping the south of Seattle. It isn't moving east or north. In the IR sat it doesn't have very high cloud tops (unlike the clouds further to the south). That looks rather like what the WRF-GFS prognostication said but a fraction wetter (or wetter later)

    The air temp is still above freezing but I presume the snow level is now at the surface for most of the metro area. But that snow that's hitting the surface is wet and soon melts. There has been no snow accumulating on Capitol Hill at 300 feet. The accumulation is the issue not that we have a bit of frozen precip that makes it to the surface (where it finishes melting).

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  36. Third comment on this entry ... about the (possible) artifacts in Rainwatch 24 hour precip accumulation.

    KATX radar switched to "clear air mode" at 1638 and has been running in that mode until at least 1935 (as I type this). I suspect it will be like this for the rest of the night. The maximum return from precip is +28 dBz or less i.e. not much precip especially for wet snow.

    There is still mostly+16dBz precip (with some +20dBz showers) over the South Sound (Seattle and further south).

    The "artifacts" are growing an seem to be at a constant radius from KATX and have continued to increase in intensity (as Rainwatch sums them up). You can see this if you run the 24 pcp as a "movie".

    Looking at the live radar from UW (or Wund) I don't see anything that matches up with that intense band hence my thinking it's not real.

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