December 21, 2020

Superfront Brings Snow to Western Washington in Unusual Conditions

 It is snowing around Northwest Washington....from the northern Olympic Peninsula, to Victoria and the San Juans to Whatcom County....and central Puget Sound is next.

And you can thanks an extraordinarily strong front for the white action.  This is very good example of how precipitation intensity can bring the snow level down to the surface when temperatures are right on the edge for snow.

But first some pictures to "warm up".

Here is a snowy scene near Bellingham from a WSDOT cam looking at I5.


And definitely some snow around the Peace Arch near the international border.


Plenty of snow at the WSDOT site on the northwest Olympic Peninsula


And there are many reports of snow around Port Angeles...some folks have an inch already.
            Picture courtesy of Rick Sistek in Port Angeles    

An extraordinarily strong front is moving through the region right now with an INTENSE temperature gradient and driving rain.   Rain is hitting my windows in waves and there is practically no visibility.  My little dog is getting scared from it.  

Here is the latest radar image (from Radarscope).  Wow.   Red is intense rain...and I can assure you I am observing that right now.


There is an extraordinary temperature change across is front.   As it crossed the WA coast near Forks, there was first a warm frontal passage (temperatures zoomed up) and then as the front went through the bottom dropped out.  

And now it is happened here in Seattle.  I can't believe this is happening....the temperatures are dropping so rapidly the windows in my office are clouding up....I have never seen this (see image).


And look at the observations on the roof of my building (below).  During the past few minutes, as the winds switched from southerly to northerly, the temperatures dropped from around 14 C (57 F) to 5 C ( 41F)...and it is still dropping.  You just don't see that around here very often.


An hour-old map shows the contrast: 56 F a the UW, but 41F near Edmonds...with a 180 degree difference in direction.  Impressive.


The last NOAA HRRR forecast for total snowfall by 8 PM tonight is shown below:


Even near sea level, some wet snow could well mix in.   But I must stress that snow accumulation will be much less, particularly since temperatures are so warm.  Here is the predicted snow depth at the same time.


Anyway, a really exciting situation.  And keep in mind that only because intensity is high--resulting in mega cooling from melting and evaporation, is snow able to get to near the surface for these marginal temperatures.

Thank the superfront.



19 comments:

  1. Snowing in Whatcom county. The temp dropped almost 10 degrees in a few hours. Radar looks like precip will continue for quite a while. This could get interesting...

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  2. It's been snowing on South Hill in Bellingham for under an hour and we have just shy of an inch on the cars and slightly less on the ground.
    This pattern reminds me very much of the Nov 26th 2006 snowfall when the Bellingham area picked up about 8 inches in 5 hours...

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  3. wow heavy rain in bellevue, i really hope it snows, or at least a few flakes....

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  4. Heavy rain (2" since midnight) turned to heavy snow near Sequim. Slush City!

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  5. Wow, pretty amazing switch in weather! I captured a time-lapse from my balcony webcam (138ft MSL) here in Kirkland. The camera is looking N-NW and takes an image every 5 secs (at 60fps). Starting at 2:00pm it is about 55F (readings displayed upper left) and a southwest flow. You can then clearly see the transition at about 2:40pm about 7s into video. That was cool!
    https://labweather.com/media/coldfront-2020-12-21.mp4

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  6. It's been oscillating back and forth between snow and rain for most of the afternoon in Victoria, BC. There's a lot more snow at higher elevations with the attending power outages and traffic accidents. You're right Cliff, this is a remarkable weather system. It's not very often that you get snow here without an established arctic outflow.

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  7. The snow around 2pm was intense on central San Juan island, 300 ft elevation. Really wet huges flakes some 3" across. As far as the noaa snow model goes, it nailed the blob on SJI. Now, branches are breaking out of trees along with heavy lumps of snow. Wild. And that after the rain... local station at trout lk. measured 2.5 in today when the front parked on us.

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  8. Would be curious on how the weather models messed this one up. Yea unusual conditions, but I don't really need fancy models to just say the obvious. 36+ on top of my baker ski resort at 1 pm, and snowing at the i5 border crossing.. seems like our modeling tries to be good most of the time.. unfortunately that is when it does not matter, the modeling should focus on complicated conditions.

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    Replies
    1. Messed up? These were stunningly successful forecasts

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    2. Cliff, I think your blog did a much better job at informing us about this snow event than NOAA and weather.com. NOAA did not have snow/rain in the forecast until this afternoon for North Seattle. weather.com did not mention snow at all for Seattle. Yet there is currently snow on the ground in some locations in North Seattle, which is consistent with the models you presented in your blog. Your blog is a huge service to the community!

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  9. My weather station has that same temperature graph in Fauntleroy. I thought it was so cool I sent copies to a couple people. At the rapid drop in temperature, there was a maximum rain rate of 4.54”/hr for a couple minutes, it was insane.

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  10. I have NO idea when it began the switch over to snow but when I went to the store after 3pm in Tacoma, it was still quite rainy here. But around 8:15pm or so, I opened the back door to drop some food scraps into my food scrap bucket on a table just outside the back door and saw snowflakes. Not showing anything in the grass as it's too warm since we were in the low 50's earlier. I thought I saw a reading from my phone about an hour earlier that said 36F or something like that, but feeling closer to 28F or something like that and recalled noting, wow, the temps sure did drop in a hurry. Well, now I now. :-) At 3:15pm, the rain was was coming down pretty good then and it's still quite wet out there in T-Town.

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  11. Just checked outside and there's still maybe 1/2 to 1" of snow on the ground in Maple Leaf in N Seattle at almost 9PM. The snow on the streets has melted. Slightly above freezing on my front porch, about 8 feet above ground level. All in all, a pretty exciting afternoon with snow coming on the heels of heavy rain and stiff breezes.

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  12. We got about 0.75 - 1.0" snow on the ground in South Hill by 2000 hrs. Our elevation is just under 600 ASL.

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  13. Snow at my home in Bellingham, but oddly rain/snow mix up at the Mount Baker ski area, and rain at Stevens Pass. I thought that they would have a huge amount of new snow up there. Was this some weird kind of temperature inversion?

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  14. East auburn about 500ft, yesterday we dropped 15 degrees in about 15 minutes. Ultimately dropped from 58 and pouring rain with south winds around 2 or 2:30pm down to 34 by 6pm with heavy snow and north winds.

    Pretty incredible to watch that transition. I was glued to my weather station and the window....and watching the outdoor american flag whip a 180 during that transition. :)

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