December 18, 2008

Seattle's turn and this weekend

Right now there is a band of snow over central Puget Sound...including Seattle...produced by convergence over the area...but with a twist. Take a look at the surface map. Instead of converging airstreams from off the Pacific, we are getting convergence between southwest flow from off the Pacific and northerly flow from the Strait of Georgia and the Fraser River Valley, with the northerly airstream being rather cold. The convergence is producing a band of snow around Seattle--which is not good for the morning commute. (see radar image) The northerly flow is occurring because the low pressure trough has moved south enough to draw the BC flow southward. The convergence zone band should move southward and weaken later this morning and the Puget Sound region will be left in scattered snow showers. But an inch or two is possible.

The latest infrared satellite picture shows the swirling clouds from the low. You can see instability clouds (cumulus type) develop offshore around the Queen Charlottes as cold continental air goes over warmer water. See the clouds over Las Vegas? They had record SNOW there yesterday.

There have been all kinds of comments about the accuracy about yesterday's forecasts. But even the most critical must admit that the models were absolutely correct about the rainshadowing over Seattle....take a look at the output graphics of my previous posts. Seattle should never have cancelled school. The model underplayed the Whidbey snow...but was correct in showing greater amounts north of Lynnwood and over the south Sound. The timing of the convergence zone snow in the north Sound was off (the models were too early by roughly 3-5 hrs). Twenty years ago we could not have provided any of the regional insights into this event...the models didn't even have the local terrain right. A major problem with weather prediction now is communication....and yesterday shows that my profession needs to do better at that. And communicating uncertainy has to be big part of it.
Now a really threatening even is possible for Saturday night and Sunday. Not a wimpy convergence zone...but a major pacific weather features coming in while cold air is over the region. The models's indicate a threat of serious snow over the region....but this is a difficult forecast. Will the cold air hold as strong, moist SW flow invades aloft? This is what we will have to determine in the next few days.

PS: Book availability. A number of local books stores and online locations have run short of my weather book. During the next few days there should be a major restocking as the 5000 printed last week become available. Some local stores like Barnes and Noble and Edmonds Book Store still have copies.


  1. Cliff,

    Great book and great site. There must be ten or twelve people I know who check the blog- the cold snap and south sound snows certainly have spurred interest.

  2. What is with the lightening and thunder this morning! It was extremely bright and loud. It doesn't normally do that here, and from my time in Utah, it doesn't normally accompany snow, at least there.

  3. Here in Freeland I have almost 5 inches on the ground and it's about 25 degrees. Thanks for keeping Whidbey Island on your radar---wish the networks would mention South Whidbey and not just North Whidbey, as the two areas often get different weather. And I don't think lumping us in with Everett/Lynnwood works well either, as those forecasts often don't work for us.
    (My verification word this post is "woosses"----is that appropriate or what? I hate driving in this stuff!)

    Snow in the PNW is so different from snow in the Colorado Rockies, where I spent 34 years. It's a bear to drive on this stuff.

  4. It was exciting for me to understand your blog this am about the Frasier River cold and the wet because I have started your book. Through chapt. 3. It is terific! JR

  5. Hi Cliff -- I'm addicted to your blog! As for your comment about Seattle canceling schools, I believe it was the right thing to do, given that there was no way of knowing early in the morning that the models were off by several hours.
    It would've been daunting to get all of those elementary kids home, then go back to the middle schools. Wouldn't want my kid on a bus in snow.
    The street in front of our school - on top of a hill - was an impassible sheet of ice for three days.
    Just my 2 cents. Thanks!

  6. Yesterday's Seattle, Bellevue, Mercer Island snow shadow was predicted and predictable just as you related -- the convergence zone happens!
    This morning, though, and specifically the last hour and a half was totally unpredicted! Snow thunder?!?! The talking weather "experts" on KING-TV and elsewhere were as surprised as those trapped drivers on 520.

  7. Cliff
    I have enjoyed and learned from your enthusiastic observations of weather for many years. Your explenations of why things happen have helped me understand this wonerful thing. Thank you

  8. An interesting tidbit...the convergence zone snowstorm of Dec 18 1990 was also accompanied by thunder...thundersnow! This is not as unusual as you might think. Here is western Washington we have as much thunderstorms in the winter as the summer.

  9. Brian R: I remember distinctly that when the storm in December in 1990 hit the downtown Seattle area, there was lightning as well.

  10. Cliff,

    Just found this website this morning, I can't believe I haven't found you before. What a resource!

    Look forward to checking back here during our upcoming winter storms.

  11. With all of the Doppler and other satellite tools now available, pray tell, why couldn't the talking head meteorologists predict one hour ahead of this "event"? I was watching KING TV, KOMO TV, and KIRO TV and none of them saw this coming... until it occurred.

  12. BTW, never forget the 1990 storm.

    I de-planed at SeaTac to light rain and wet ground. By the time we reached Tukwila it had turned to an absolute blinding snow.

    I-5 became an impassable parking lot about 2 miles south of the brewery in whiteout conditions.

    Somehow we made it up over First Hill and onto Rainier Ave, and I remember seeing hundreds of abandoned cars, high winds and lightning.

    Got home to 12 inches of snow on Capitol Hill, 8 HOURS after leaving a bare and wet Sea-Tac. What is that, 15 miles?

    The convergence zone is amazingly powerful in such a micro environment.

  13. Cliff, I was on a team that had to make the call about closing school. We had to do it by 5am. At that time, the forecast had snow for the afternoon, with the PSCZ possibly moving south. I voted to start an hour late, but get everyone out by 2pm or so. However, the fear of kids being trapped at school trumped my vote.

  14. The cold air/warm air boundary came over CapHill this morning at 5:30AM with two low/close lightning flashes and thunder. Not sure if that was a strike on the TV towers (about the right distance from me).

    You can see the motion of the snow in the temperature observations at Boeing field (KBFI) just after 6AM and Seatac (KSEA): the latter dropped 5F in 35 minutes at 7:53AM.

    At 8:30AM we have perhaps 3 inches of snow on the ground (at 300 ASL foot or so). Looking at the radar it looks like we have changed to discrete snow showers moving in from the SW.

    Snow is falling as I type this.

  15. Anonymous @ 7:18 AM,

    I too was surpised like the talking heads, and I hate to defend local news folks. From 3am-4am, I watched the radar and saw a band of precipitation leave a dusting of grapple on my sidewalk near Green Lake. I didn't see anything else on the radar, so I went out and swept the sidewalk for 1/2 hour. 5 minutes after I was done, the radar showed a big band of snow heading my way, and it continues at the moment. In the span of just about an hour, the radar went from clear to full blown convergence zone snow. Soon I will be out cleaning the sidewalk again.

  16. Regarding communication, is it true that the news team anchors on the local morning TV news reports are all from California? They seem awestruck by the weather today and leave the impression of dire problems throughout the "region". Yesterday they seemed to be amplifying the potential for bad conditions. The weather folks were less so. There must be some decision-makers at the school districts affected by the TV personalities' comments.

    Keep up the good work and we'll stay tuned for the balance of the week's weather reporting.

  17. Hi Cliff,

    I was involved this morning as well in a decision to close schools. One thing that caught my attention was the 4km MM5 was showing a narrow band of relatively heavy precipitation between 7am and 10am right over Bellevue and east, with a little less into Seattle. It obviously didn't catch the convergence zone exactly, but I was pretty impressed!

  18. That thunder this morning was awesome, in the traditional sense of the word. I happened to be awake in bed when it struck. It seemed to encompass my building. The whole structure shook, and the windows rattled. I was terrified. I have never experienced thunder that seemed to actually encase a building.

  19. I am in Bellingham, we have over 10 inches of snow (4 inches left over from the weekend). Forecast for 4-7 inches of snow was spot on for us, though the timing was a little off, but who cares.

    One thing about closing schools yesterday for Seattle. What happened in Bellingham was exactly what Seattle was concerned about. In the morning, the snow was light, and not a lot of accumulation overnight. But around 9AM, the snow started, by 11AM it was coming down very hard, and stayed snowing hard for awhile. So, the morning commute was easy, the afternoon was very difficult. A lot of places closed early.

    Hoping we get more snow over the weekend, and hoping the mid week system dives a bit to the south, so we get colder air behind it instead of warm air.

  20. The TV weather folks here have apparently taken their clue from those newsfolks for whom "if it bleeds it leads" is the motto that they live by. Inducing panic and having a "severe weather center" is just inexcusable.

  21. Cliff, can you explain the map with the observations that have circles and little tails on them. Is that wind direction and severity?(I don't have your book- it's sold out everywhere I checked). Congratulations!
    Thanks for a most interesting site!
    Susan L.

  22. Interesting to note that today is the anniverary of the 1990 storm, and that the only two times I have noted thundersnow in my 35+ years of taking weather observations on Beacon Hill in Seattle was during that day in 1990 and today!

    This is a truly historic storm,not so much in Western Washington,but in Spokane.Cliff, did you notice that Spokane (GEG) absolutely shattered a 127 year record for 24 hour snowfall: 19.4 inches(and possibly still to go higher).It broke the existing record bt more than six inches. Incredible!It looks like that youl`ll have to have a chapter on the Great Spokane snowstorm of Dec 2008 when you update your book in the future.
    One question for you. Why did the NWS drop the winter advisories, when conditions dictate that they should be upgraded to a warning? I just swept my snowboard--4.3 inches of snow in the last six hours, and moderate snow showers are still occurring.It looks like my storm total, judging by the snow band training on the radar, may well exceed 6 inches, and a lot of other neighborhoods in and around Seattle are experiencing the same.

  23. Absolutely POURING snow here in downtown Seattle.

  24. At Salmon Bay (sea level) it's been snowing all morning. I haven't measured, but it looks to be at least 2 inches. The snow seems drier than past years and it's landing on frozen ground (Making the roads slicker than they appear). The winds started picking-up at about 10:00 am and the quality of the snow has quickly changed from pretty flakes to something stingy and more sleety. Cold northerly winds are whipping across Shilshole, through the Salmon Bay waterway, and really blasting the Locks.

  25. Hey Cliff,

    Is there somewhere on the web that us weather novices could have access to the same radar and satellite images you post here? I use the NWS site for radar ( and a Unisys weather site for satellite (, but the products available on those sites are nowhere near the quality of the images you post here.


  26. The Edmonds school district closed yesterday--it didn't look the like right call either. But around 3pm, the snow started and by the time my daughter would have been dismissed, it was pretty snowy. So all is well that ends well. But it was close, obviously for most of the day the roads were fine. I think that on balance, the extra dismissals have simply extended the Christmas break--I know you're a big proponent of stronger math skills for kids, and every day at school counts, but the truth is with flurries in the air, some days count for less. The kids probably were not getting much done--they get really squirmy and lose attention just before the holiday, especially with wintery weather.

    You're right about your model--the shadowing was well done. Are you still running an ensemble of solutions at the UW? Or is the WRFGFS or the 'WRFNAM' a lot better than the other members anyway?

  27. What a great blog! Thanks for writing it.

    Re: Your book - the publisher needs to provide some to Amazon. I ordered several as Christmas gifts three weeks ago, and Amazon can't get them to me until after the holidays, cos it doesn't have any. So I have nothing to give several folks on Christmas. Major bummer, I thought your book would be the perfect gift!

    But good for you the book is so popular. Happy holidaze!

  28. For those having problems reading weather maps and understanding wind barbs Wikipedia is a good introductory source (and you can improve it if something is missing).

    For example:

    I suspect Cliff should add a few of these (selected) links that answer FAQs.

  29. Silly me--the ensemble page is indeed working, there are 8 out of 9 solutions avaiable at the moment (I'm looking at precip). I had looked the other day and only a few members had shown up, but I probably checked too early.

    If I am not mistaken, probcast is based on this--correct me if I am wrong. It is easy to get out of the habit of looking at the ensemble members. I don't think I have used it much since the big success of the forecasts for the Hanukkah Eve Wind Storm of 2006. If I remember correctly, at least five members had nearly identical windstorm scenarios, which is very good agreement indeed, imo.

  30. Cliff,

    Great call yesterday morning! The snow-shadow absolutely happened as the model suggested and Seattle should not have closed schools. My family lost a day's wage because of the "no-snow day" yesterday. Granted, plenty of school district employees live outside the city and their commutes may have been less than ideal, but there is no reason an early dismissal couldn't have been called to get those folks back to the eastside on time. Keep up the good work Cliff.

  31. I have been closely tracking the NWS forecasts this week and last. Cliff explained that there was a "communication" problem. Well, I guess if he meant that when the NWS updated its forecast it put completely wrong words in its communications, I would agree.

    For example, Tues thru Wed morn, I watched the NWS forecast go from something like 90% chance of snow (1-3") to 80% chance to 80% chance of rain. Temps were forecast to be 31, then 34. What I observed was around 40 over a wide area of the west Sound Wednesday afternoon.

    On Sat morn, the NWS forecast called for snow in the early afternoon. I have seen several forecasts of 100% chance for a particular condition not pan out this year.

    I understand these models are not perfect, but one can hardly be surprised when people don't take them seriously when they make 90-100% forecasts that aren't close to what actually happened.

  32. Cliff -
    Usually I'm one of the nay-sayers about snow in Seattle. In my 20+ years of living in Seattle, whenever the forecasters say "snow" they're wrong.

    Reading your blog I feel like I finally have an insight into where these weather predictions come from. It's not just a prediction - you show me the data, not the data filtered from the computer to the National Weather Service filtered again to the news agencies and then reinterpreted by TV weather anchors.

    Sure the model was off by a few (a lot) of hours, but you were clear with us as the updates came through. You told us exactly what the model said, and exactly how that changed over time.

    My gosh, weather systems are complicated beasties, I can't believe we know anything more than 5 minutes before it happens.

    Keep it up, I love seeing the data and having you explain it.

  33. (This is for tipo158 concerning the wording of NWS forecasts)

    You might find differences between the zone forecasts--which is most of the time looked at pretty carefully by a forecaster, and the point and click forecast (where you click on a map). There are often differences between what a human forecaster will type up--to give a general forecast to a zone area, while the point and click "digital" forecast is generated in a completely different way. It is not unusual to find differences--for instance, I often check the forecast in the mountains, and because the point and click forecast can have large differences from pixel to pixel because of elevation changes, you can actually get strange forecasts (for instance rain in the pass, when the zone forecast says snow level 2000 feet). That was a problem in November. It is exceedingly time consuming to double check a lot of 'grid' points to make sure then come out okay. I check on my home, Mountlake Terrace, to be sure it comes out okay, but it is a bit of a tricky system. You can always watch the TV guys, or tune in on this blog, or go to Accuweather of course and compare. I'm one of the general forecasters at the NWS, and you can be sure that, despite rotating shifts, and many gigabytes of model data, we do make an honest effort to get it to come out okay. Sometimes it works, sometimes there are glitches.


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