December 17, 2012

Now Lowland Snow Showers

Cold air has moved in behind the low pressure center;  in fact, the atmosphere is now cold enough that snow can reach the surface in heavy convective showers.

The latest visible satellite picture shows lots of convection in the cold unstable air approaching the region.
 We now have strong onshore flow of  cool, shower-filled air with marginal temperatures for snow.   The snow level is now around 1000 ft, but heavy showers can lower the snow level by melting and evaporation.  Snow showers have already begun around the region

The flow is generally westerly, which means heavy snow in the Cascades.  But there where will be some locations like Seattle, that will be in the rainshadow (snow shadow!) of the Olympics.

Here is the UW WRF model snow forecast for the 24 hr ending 5 AM Tuesday.  Some snow reaching the surface over the lowlands, but not much.  Lots in the Cascades.

 What if the model is wrong about how much snow reaches the surface?  Lets look at how much total precipitation the model is forecasting over that 24-h period.  You can see the rainshadow around Seattle.

So bottom line:  don't be surprised if there are few snow showers....even some light accumulations away from the water and on hills....particularly away from the lee of the Olympics (e.g., Seattle).

The threat of lowland snow doesn't end tomorrow AM, here is the predictions for the next 24h:


  1. Thunder & lightning in Snohomish - no snow yet, but chances are looking stronger!!


  2. Hmmmmmmm....snow in Eatonville. Only about 1/2 inch so far but at 32 degrees anything that falls tonight will be frozen! Wondering if schools will start 2 hours late...they cancelled the middle school band concert tonight. Will we get an extra day of Christmas vacation?

  3. As they say, bare and dry in Bellevue. Actually, the moon and a few stars are out too! I don't care if it snows a little, but I have a big deadline with co-workers in Washington, DC, and the Ukraine... so I need to get it done, regardless! LOL

  4. Fairly heavy hail in Anacortes.

    I took a picture of the Guemes ferry in the winds this afternoon in Guemes channel. Wind against current. Would not want to be on that ferry (100' and tossed around like a toy.)

  5. We've got a little more than a dusting here in Lakeland Hills in SE Auburn. Plus it was snowing in Milton & Edgewood around 10 PM.

  6. Wanted to report we had thundersnow here in Bothell. The snow was mixed with sleet and rather brief but the thunder persisted for about 30 mins. This is supposed to be a rather rare met event. Would welcome your insight!

  7. Nice snow shower in South Bellingham right now at 200' ASL.

    Not really sticking though. The same happened overnight as well.

  8. SE of Chehalis, up about 620'. Started snowing last night about 9:30. Big fluffy flakes. This morning, 4-5" in the yard, depending on where I measured.

    Sun's out, now.

  9. Just started snowing here in Bellingham.

  10. We got a dusting in Shoreline, in the Ridgecrest area (~400 ft). Just on the grass and the streets this morning didn't feel icy.

  11. Tacoma had about half an inch this morning and the roads were VERY icy before the sun came up.

  12. Whole lotta nuthin' in West Seattle. Boo!


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