Tuesday, November 23, 2010

Midnight Update

Monday, November 22, 2010
11:50 P.M.

So the snow has now largely come to an end. Don't be surprised if you see a flurry, but I doubt you will see any additional accumulation.

Generally, I've been hearing of about 5 inches of snow in the Seattle area. I have 5 inches at least. Very, VERY cool stuff. I'm pretty darn happy right now. And the mountains are getting tons too.

This has been pretty crazy. This much snow this early. Let's hope that it is a precursor of things to come. I think I already said this too, but Barrow, Alaska was warmer than Seattle today.

The big stories now are going to be cold and wind. First, let's look at some temperatures. This model below shows the 7:00 A.M. (generally coldest part of morning this time of year) temperatures for Tuesday morning. Seattle will likely get down to 20 degrees or so. Even areas near the water will still be below freezing.

By the way, tomorrow will feature SPECTACULAR visibility. The atmosphere is very dry, there is little air pollution, and it will be completely sunny. There will be a marked difference. When you don't have humidity or particulate matter clogging up the atmosphere, you can see a lot further. That is why deserts (except when they have dust storms) are often very good for viewing stars - very low humidities.

The day after tomorrow (haha) will be even colder. Here is the same chart 21 hours later (the morning low will occur earlier because the sun will be out).
Even colder for Seattle! You can already see warming off the coast - that is part of the high pressure that gave Barrow a high of 34 today coming in. Yeah, it's that big of a high pressure ridge. But in Seattle, lows will get into the mid teens. Outlying locations could get to 0 degrees.

This graphic shows how dry the air mass is by measuring the RELATIVE HUMIDITY of the atmosphere. It is for mid-morning tomorrow. See that orange around us? It means we have a relative humidity of 25 %. That is extraordinarily dry. And colder air masses hold less moisture (90 degrees 100% relative humidity is much more humid than 50 degrees 100% rh) so a subfreezing air mass with a relative humidity of 25 % is extremely dry.
Haven't shown the relative humidity graphic before. It's a cool one. :)

Now - winds! The saga never ends. The winds are blowing like crazy up north right now, as this graphic shows. This shows what was forecasted for 10 P.M., so it is actually an old graphic, but that is when the winds peaked and this is how fast they were. Note - these are SUSTAINED winds. Multiply by 1.5 to get gusts (approximation).
You can see a very localized, but intense, area of winds up north.

These winds will weaken, but winds will spread throughout Puget Sound Tuesday as this graphic indicates.
It will be cold and windy, especially in the sound. This graphic doesn't show Seattle getting real strong winds, but all you need to do is shift the gradient a little, so I would still be on the lookout for some gusts tomorrow. Places over water, however, will take the main beating. These winds, however, will be nowhere near as strong as the ones being witnessed right now over the San Juans. A high wind warning is in effect for those areas right now. Winds over most of the sound look to be below advisory level for most of the day (except in that dark band of blue and green).

One last graphic - the 1000-500mb level thickness model is regarded as "the" model to determine the true strength of an arctic outbreak. Simply put, it measures the temperature of the lower atmosphere. More complexly put, it measures the distance in decameters from the 1000mb air pressure level to the 500mb air pressure level in the atmosphere and calculates how cold it is based on the distance, with a lower distance being colder (cold air is denser, takes up less space) and a higher distance being higher. Heat waves generally have a value of above 580 decameters in Washington. You have to start thinking about snow when it gets to 522 dam (dam=decameters). Right now, it is like 507 dam. That is extremely low.
This is for tonight at 1 P.M. As I write this now it is 12:51 A.M. Yeah this has so far taken me one hour, but I enjoy doing it. I was watching the Bourne Trilogy but decided I'd rather write an update.
You can see that there is clearly a lot of arctic air in Western Washington. If this was in December or January, I would seriously be concerned about highs getting out of the teens. No joke. They might reach twenty. But we are gonna get an arctic blast that has not been diluted too much.

Wow! The models actually showed this 16 days ago. Not this exact scenario, but this idea. Pretty crazy. Then they shifted to highs in the 40s, believe it or not. There is not a lot of data over the arctic, so models commonly have problems with these situations. Given that it is a La Nina year, I expect that we will see more arctic outbreaks. This is definitely a good way to start. :).

To wrap it up - cold tomorrow and FRIGID Wednesday morning, before moderating while remaining mostly dry through Wednesday. A more active, typical storm track will return after a system affects us on Friday.

1 hour, 12 minutes (now I'm going to post how long I've worked on these. Hopefully someday I can count them all up. :)


  1. Good post! So it sounds like the snow and ice will stick around on the ground through Wednesday?

  2. wooo a commenter!!!!
    Yes, it does.
    I signed up at SkyscraperCity, I posted my blog there.

  3. Nice! Thus so far it seems that your predictions have been much more accurate than the mediocre ones of professional weather services. Keep it up! Also how do you think this will affect the chances of school on Wednesday?

  4. Yeah, Charlie - I think we are all wondering the likelihood of school on Wednesday!!
    What are your thoughts?

    Julia :)

  5. Very very low. Like, in the negatives. The roads are frozen solid.