November 19, 2010

Uncertainty

Tonight light snow and strong NE winds has spread from the Bellingham area, across the San Juans, to lower Vancouver Island....and the next to be hit is the northern Olympic peninsula. The model forecasts were quite good for this. Here is the current surface observations...you can clearly see the NE winds exiting the Fraser.
Saturday and Sunday is really going to be pretty dull around here...not much action, snow-wise or otherwise. And we know that cold is coming and Tuesday morning will be cold enough to produce a hard freeze. The question is snow late Sunday and Monday.

Until this morning, the models showed too little moisture on Monday for any real snow. But now there is some disagreement. The NAM model has a much stronger upper level wave moving down the northerly flow along the West Coast, compared to the GFS model (which is usually the better one). One has a few light snow showers, the other more serious snow. I would generally bet on the GFS model...but we have time to see which solution dominates. Want to see the difference? Here are the two:


Pretty subtle? But a world of difference. There disturbances are forming over the arctic where we don't have that much data. Sometimes we have to live with uncertainty in forecasts and this is one of those times. I expect by Sunday we will know what will happen...enough time to prepare. And I will start using and showing you some of new high-tech tools for dealing with uncertainty...ensembles forecasts with statistical postprocessing!

25 comments:

  1. were it only possible to use those high-tech tools for dealing with uncertainty in non-meteorological areas of one's life...

    looking forward to the upcoming posts! the 5 y.o. is still hoping for snow, but now knows we need cold AND "water in the air" (her idea: why don't we take some water from the house and throw it up high to MAKE snow???)

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  2. Yep - snowing like crazy in Bellingham for the last 1.5 hours - we're loving it!

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  3. I'd definitely say Bellingham downtown is getting heavy snow right now. 3 inches of wet stuff in the courtyard of my building.

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  4. We're up to a good 2 inches in downtown Bellingham. The Fraser wind seems to have tapered off a bit from earlier but it's still there.

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  5. About 4 inches on South Hill in Bellingham, and still coming down. Radar is promising more to come!!!

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  6. At least two-inches over near the Civic Athletic Complex in Bellingham, and it's still coming down pretty good.

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  7. We have around 3 inches on the ground and still snowing like crazy in Bellingham. Take that, snow Grinches! I had to clear about 5 inch drifts from my hood and windshield and navigate crazy slippery roads, some in deep unblemished snow, to get home. Love it! Is that what is meant by light snow? : )

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  8. The northwest side of Bellingham picked up 3.5" in 3 hours. The snow was moderate to heavy at times.

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  9. I'd say Whatcom County got it pretty good.

    http://i7.photobucket.com/albums/y287/thunderbird107/whatcomsnow.jpg

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  10. 08:30-first flakes falling in Sequim, land of the smug!

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  11. As predicted, Jim Forman on the scene in his yellow arctic parka producing a heavy downfall of hyperbole and fear. He cautions everyone to stay home.
    What a shame he is the intro to Jeff's forecast.

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  12. I'm 15 miles NE of Bellingham, and we got only about an inch of snow. Unfortunately the howling north winds have polished that snow into solid ice on the roads, so it's treacherous driving. No sand trucks yet, so I had to bail on my grocery run to town. Melt please!

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  13. Orcas Island, Mount Constitution, 25 degrees, approximately 3 inches of snow, windy and clearing... well here we go for winter 2010-11

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  14. For a complete weather novice the line "Want to see the difference" made me chuckle because when I look at the two models all I see are "Oh, more pretty blue there than there" and "The pretty squiggly lines move differently." I am going to click on them so they are larger and see if that helps me understand them better. I am fascinated though by the fact that we even have models that can predict weather to begin with. Also, I seem to be the only adult in Seattle rooting for snow in town.

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  15. I've always wanted modern tools to help me deal with uncertainty!

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  16. Do you have a link you can share on where we can look at current GFS and NAM maps? I would love to view the most current model runs as I read through the weather service discussions... Thanks,

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  17. natch, I gotta say, being from the Northeast, the idea of a 5 inch snowdrift is pretty funny. Only in Bham...

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  18. City of Portland seems fairly sure we will have enough snow down here to require clearing it. They've chained up their entire fleet, hung all their plows and their spox said "we're convinced it's coming" (yesterday, on the noon news).

    The City uses AccuWeather, which we can't get without a subscription, so AW must have validated the NAM...

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  19. I trust all saw and enjoyed this:

    http://www.seattlepi.com/fun/comic.asp?feature_id=Bizarro

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  20. sdpontiac said "Do you have a link you can share on where we can look at current GFS and NAM maps?"

    The best page is at this link http://www.atmos.washington.edu/data/wxdisc.cgi. You have obs, sat, radar, global model output and some mesoscale model output all in one place.

    Check out all the links on the page (especially those at the bottom the link to the "data" page is a great source of links to all their weather obs, forecasts.

    All of the mesoscale model output is at http://www.atmos.washington.edu/mm5rt/

    Perhaps the best thing to follow along is the "WebAFD": an illustrated version of the National Weather Service Area Forecast Discussion.

    In the AFD a forecaster at the NWS (in this case the Seattle office ... SEW) explains his thinking behind the current forecast (once per shift) and possible issues or problems with the forecast. Read the text and look at the images (screen caps from their workstations). You can also see some of the forecaster rules of thumb (the current one is 1000mb to 950mb thickness less than 1300m is cold enough for snow). Even better the AFDs often are humorous.

    You can find the current Seattle Web AFD at http://www.wrh.noaa.gov/sew/gafd/latest_webafd.html

    Of course a good intro to meteorology helps by putting the basics in place. Looking at a pretty plot of the expected vorticity doesn't help if you don't know what vorticity is or why you should care. Or why people would want to know what the layer thickness is.

    Hopefully the rush to view the data won't flatten the UW servers. I for one am really grateful that all of this info is published outside of the firewall. And they do take donations too to support their network costs.

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  21. Cliff, I'm jonsen' for an update. Have an 8:45am class Monday, and have a paper due!

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  22. City of Redmond has deice solution on SR 202 as of around 5:15. Van reads 37 degrees

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  23. All I can say is remember
    Remember remember remember
    The mistake
    That Nickles maaaaaaaaade

    When the streets
    Turn to rivers of ice
    Get out the sand
    Get out the shovels
    Listen to me businessmen!
    Or your Xmas shopping season
    Will be fraught with slippery danger!
    (Danger! Danger!)

    ...
    (sorry, just spent the afternoon listening to complaint choirs of the world)

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  24. I emailed the weather service on Wednesday to let them know they were underestimating the wind speeds for this weekend for the San Juan Islands. NE 10 to 15 mph just didn't cut it. Then they upgraded it on Thursday to 15 - 25 with gusts to 35 as I had suggested. Then they downgraded back to 10-15 mph yesterday morning. And then finally they realized their mistake. Too much now forecasting on wind speeds this past week.

    Ferdi Businger, Sinclair Island

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  25. Cliff, your sheer number of page hits should tell you that we need another update! Since we keep checking, we obviously love your forecasts!

    Especially in times like now!

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