December 23, 2021

Most Will Have to Dream of a White Christmas

Detailed update this afternoon....I will have the forecasts from the more powerful high-resolution forecast models by then....

___________________________

I have some disappointing news for many living over the western Washington lowlands.

Saturday, December will not bring extensive lowland snow on the ground.

On the other hand, many of you will enjoy seeing snowflakes falling out of the sky, which coupled with a rendition of Irving Berlin's classic music and some hot chocolate, might be enough.

Not this year.  Picture by Steve Voghut

Large amounts of snow are expected in the mountains, so snow recreation will be excellent and close.

Snow 101

The temperatures during the next few days will be marginal for snow near sea level, which is often the case in our region.

In addition, the ground temperatures are relatively warm, as illustrated by the current soil temperatures from the WSU AgWeather network, which are in the low 40s in the west and mid to upper 30s over the Columbia Basin (see below).


The distinction between snowfall (amount of snow falling out of the sky) and snow depth is an important one, with snow depth often being MUCH less than snowfall.   

First, in marginal situations, the snow is already melting before it hits the ground, with above-freezing air temperatures within the lowest few thousand feet.  This will be the case during the next few days.

Second, light to moderate snowfall is melted by the warm surface.  This will happen as well.

Another issue is model resolution.  The waters of Puget Sound and the Georgia and Juan de Fuca straits are relatively warm (around 50F).  Furthermore, these water bodies are relatively narrow...so narrow that many models do not have the resolution to include their warming properties in the forecasts.

In addition, the lack of resolution in global models, particularly those used in global ensemble forecasts, causes surrounding terrain to "spread out" into the lowlands, producing colder surface temperatures and more snow than is reasonable.  

The Christmas 2021 Situation

The latest UW WRF model forecast is out, with the snowfall accumulation through 4 PM Saturday shown below.  This is a relatively high-resolution model (the distance between the grid points is 4 km).  Lots of snowfall in the mountains (1-2 feet) and light snow over the lowlands (under 1.5 inches) and nearly nothing near the water.

Quite a bit of snow near Spokane but nothing in the Tri-Cities.


But now let me show you the snow accumulation (snow depth) on the ground over western Washington predicted by the same modeling system for the same period. 

Virtually nothing over the lowlands, with the exception around Bellingham and San Juans, where cold Fraser River outflow helps maintain snow accumulation.


Eastern Washington snow depths through 4 PM Saturday are more extensive, with Spokane certainly enjoying a snow-covered landscape. A colder environment, isolated from the warm water of the western side.


The big issue is still the unusual cold that will move into the region on Sunday through Wednesday.  I think the models are having a problem with the event, for reasons I won't get into here, but lows of 5-10F in the western side of the state still appear viable.



28 comments:

  1. The great unwashed *really* appreciate the updates on this interesting event. Thankee Professor!

    ReplyDelete
  2. Thank you for your updates! For you who plan to head to the mountains for snow play. Check the WSDOT mountain pass reports, make sure your gas tank is topped up, and you have plenty of water and snacks and warm clothes in case you get stuck in an hours long traffic jam. Park in designated spots and don’t forget your SnoPark Pass (you can buy and print a one-day pass on the state parks website). Not having a pass and parking in the wrong place are both really expensive tickets. The state patrol/sheriffs will be out in force…

    ReplyDelete
    Replies
    1. Inslee recently fired more than 200 patrol officers so I'm not sure what you mean by "out in force" - snow parks are the least of their concerns right now.

      Delete
    2. No, they were let go for not complying with a policy to be vaccinated.

      Delete
  3. Would love to know why the models are having a problem with this event.

    ReplyDelete
    Replies
    1. Cliff touched on it already in this blog and multiple past blogs. There are a lot of moving parts required to be in alignment to get snow/cold down to sea level in Puget Sound. Unfortunately due to grid spacing (think large blocks of duplos to represent topography) on our models, lots of finer details get smoothed over. This is important when just a couple degrees can make the difference between a wet roadway or a massive snowstorm.

      Delete
  4. Happy Holidays Cliff! I'm kind of excited about the potential for another potentially historic weather event, although I hope that everyone comes through this one okay. I remember a few of the cold snaps that we experienced during the mid-eighties to early-nineties up here on Vancouver Island. It sounds like this cold spell might give those events a "run for their money," at least if the forecast pans out. Finally, I am scheduled to take a trip to Saskatchewan in mid-January, so I'm thinking of the upcoming cold snap like a sort of "weather appetizer." All the best to you and yours from a Canadian fan.

    ReplyDelete
  5. Lynden checking in; still figuring on a very white Christmas….

    ReplyDelete
    Replies
    1. Already got snow on the ground. Thank you Frasier outflow.

      Delete
  6. Thank you Professor. This helps so much. I have goats and live on an older rural property, so I am always concerned about weather extremes. Do let us know how long you thing the extreme cold will last before we get above freezing again.

    ReplyDelete
  7. I don't miss KNKX! Thank you Cliff!

    ReplyDelete
  8. Cliff, if snow prediction is so hard, how do you know you're right this far out from the event?

    ReplyDelete
  9. Hey Cliff- I have just moved to an area between Tonasket and Republic called Aeneas Valley, and we're seeing one weather app with some sketchy information. It says we'll hit -40 on New Years Day. Wx Underground is very different, and weather-got-gov isn't out that far. Do you see any part of Washington hitting -40 on New Years? Not sure what the app is, but screen shots are being posted on our local FB page and freaking people out. Closest reporting station is Wauconda, WA. Thanks!

    ReplyDelete
    Replies
    1. Just a weather app gone crazy. Don't see it happening. Certainly will get below 0 in those valleys, but not likely to be -40F.

      Delete
  10. Is the EU model still showing a fair amount of lowland snow through Jan 14? I'm guessing we won't see much snow this week with it being so cold, but maybe after it get back UP towards freezing? Lol

    ReplyDelete
    Replies
    1. That's a question I'm wondering about as well.

      It seems like we have the best chances of snow in the 3 degree range above and below 32F (exception; when a cold mass meets a wet one). But, all the indicators point to a higher chance of lowland snow this year (i.e., January), and we typically don't see those events until January 20'ish, so we still have time but...I sure would love to have Cliff's thoughts on this.

      Delete
  11. Yikes, that grapefruit tree of mine is going to have a tough time!

    ReplyDelete
    Replies
    1. Yes Ansel! I was just out mounding mulch around my fig. I discovered that bubble wrap, especially the kind sold to lay on top of the water to warm swimming pools is a fantastic insulator and heater in the garden. I even cooked a few plants to death in April before I realized its true power ;-)

      Delete
  12. Cliff, to clarify on your last comment. Do you think 5° to 10°F is possible in Seattle or in select areas in Western WA known for cold lows like Darrington, Tunwater, etc?

    ReplyDelete
    Replies
    1. Possible in Seattle, but less likely. Outlying areas still looking likely.

      Delete
  13. Just curious, do these models assume that every area is starting off with no snow? I don't live in Puget Sound, I live in Leavenworth, and the snow depth models say we will have less than 5 inches depth. We already have about 15-16 inches on the ground. Guessing we will get a few inches, and maybe that is what the snow depth model is picking up on, as in how much new depth as opposed to actual depth.

    ReplyDelete
    Replies
    1. The models predict new accumulations, so in addition to what you already have. Leavenworth looks pretty on the Webcams.

      Delete
    2. Snow depth represents new accumulation, not current.

      Delete
  14. Wow, ivw been using the UW weather models for probably nearly a decade now to decide where to ski. Ive got some rudimentry knowledge of CFD grids and never realized that the grid resolution of the weather models needs to be fine enough to pick up on localized features. This was some really cool knowledge that you shared.

    ReplyDelete
  15. Got our inch of snow last night above Hood Canal...so at least it's nice to look at.

    ReplyDelete
  16. It's dumping snow in lynden on Christmas. It's going to be nasty tonight, no relief in sight!

    ReplyDelete

Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

Lots of Lightning, A Dismal July 3rd, and a Hopeful Forecast for Fireworks

 As predicted by high-resolution weather forecasting models, there were many thunderstorms and lots of lightning in eastern WA, eastern OR, ...