wxmet

Moderate snow falling on Christmas morning in Seattle and i'm out of town. Would have been a sight to see. http://wx.graphics/models/ecmwf/2017122400/washington/ecmwf_ptype_washington_36.png

All snow on the ECMWF. The fact that the onset starts during the evening hours on Sunday helps with temps. Monday morning: http://wx.graphics/models/ecmwf/2017122300/nw/ecmwf_ptype_nw_60.png

The fact that the models are showing snow over the Pugent Sound is a good indication of snow levels all the way down to the surface.

Skew-T looks good at KSEA:

Another thing to add is the way the 500mb confluence sets up over us. The positively titled trough stretching westward over Canada and at the same time, the ridge near the Gulf of Alaska helps to drive the storms in our area with a cold air mass in place.

The setup resembles big snowstorm events in the PNW such as Nov. 1985. The key is the strong 1040mb+ high to the north keeping cold air in place as the low pressure system moves onshore.

I'll get excited when this is within 48 hours. Still a long ways out. I still don't see a strong high to the north to help keep cold air in place as the low moves onshore.

Good look to it. GFS has been trying to bring something around the time frame for a couple of runs (with timing differences). What's missing is a strong high to the north to funnel down cold air for lowland snow.

It's snow downtown here as that band is working its way in. Very light so far though.

The reflectivities in the band from the west look stronger than the one down in Pierce County. Both bands are heading into King County. Should have pretty good coverage.

Band is holding together well as it moves eastward.

It definitely will come down as snow as that's what's happening downtown now.

Closer look: http://wx.graphics/models/wrf3km/2017110512/washington/wrf3km_radar_washington_9.png

NAM 3km 12z picked up on the band from the west:

There's a nice band moving towards the Pugent Sound from the west. Should produce some nice rates.

Best banding has setup around Bothell and up to Everett. Band entering Tacoma from the south. Would be nice if it made it up here.

Light snow flurries in Downtown Seattle.

The low is just north of Astoria but is transferring to be just east of Puyallup. The 3km NAM is encouraging decreasing the 1000mb-950mb temps later in the morning but I wouldn't place bets on it. Snowing at SEATAC.

Something to watch for around 16z is an area of frontogenesis stretching from Olympic Park to the Central PSL. That would be where the best banding would occur. http://moe.met.fsu.edu/banding/t00z/nam.nw.frontb16.png

The surface low is still off-shore and looks to be on track with the GFS 00z 6z position. Temps in the mid to upper 30s in the WPSL as CAA begins.

Frontogenetically-forced band of heavy rain moving through the WPSL. Would be great if this was snow. http://weather.rap.ucar.edu/radar/nids/images/KATX/20171105_043838_BREF1_gray.png

I can see the ECMWF being right (warm low level temps) resulting in trace amounts for the WPSL. This really comes down to a nowcast monitoring trends overnight as they unfold. When does the CAA begin, position of the low, available moisture, etc.

I've found the HRRR to be terrible more than a few hours out.

Looks good so far. http://weather.unisys.com/surface/sfc_con_3pres.gif

Key thing to watch for overnight from the NWS discussion: "If strong northerly flow develops fromthe surface up to 800 mb as some models suggest, an isothermal profile should drag snow levels down to 500 feet or lower."