Cascade Snowstorm & What’s Up With Freezing Rain On 7 Day Forecast?

December 19, 2017

6:30pm Tuesday

Today’s cold front sure delivered the advertised goods!  Heavy rain & a gusty southerly wind from daybreak through early afternoon.  The cold front is moving through the Blue Mountains of NE Oregon right now.  This is the leading edge of a much cooler airmass.  No more 50s until further notice!  It appears 6-8″ snow has fallen in the Cascades and we expect more tonight and Wednesday AM:

Sticking snow could fall as low as 1,500′ to 2,000′ tonight.

We now enter a cooler weather pattern that eventually turns very chilly this weekend.  The highlights:

A modified “arctic” or polar front drops south out of Canada on Friday.  Moisture appears to be very limited and snow levels will be above the valley floor anyway so I’m ignoring that.  Then a massive area of high pressure sets up over the Western USA, check out the 1050 millibar surface high sitting over the northern Rockies

That gives us a widespread and strong/cold east wind over the weekend.  Not just in the Gorge but ALL of us in the metro area will feel the cold wind as the air sloshes right over the top of the Cascades too.  This setup could give us 30-45 mph gusts just about anywhere both Saturday and Sunday.  On a side note, the anemometer has already been replaced at Vista House in the Gorge, the Oregon State Parks people replaced it Monday.  You can find it here:

So then we get to Christmas Eve where problems COULD show up.  This morning’s run of the ECMWF & GEM both show a weakening system punching right through the upper-level ridge along the coastline.  It’s the southern part of the jet stream attemping to sneak in beneath the ridge…note the ECMWF rain/snow/cloud forecast for 7pm Christmas Eve:

Green means the snow level is well above the surface.  Probably around 4,000′ or so in this case.  There will be  cold air pouring through the Gorge at that time (the one part of the forecast with high confidence).  Assuming moisture shows up (a big assumption 5 days ahead of time), this would be a setup for freezing rain in the metro area/west Gorge and snow farther into the Gorge.  The ECMWF shows this with the ice accumulation product

The GFS has the system much farther west at the same time Christmas Eve, slower to break through the ridge:

Thus the uncertainty in the forecast!  It could be anything from a dry Christmas to an ice storm Christmas Eve & Day in the metro area.  Regardless it’ll be the coldest/windiest Christmas we’ve seen in awhile.

I’ll be on Christmas vacation (theoretically) tomorrow through Christmas Day.  I’ll be around the area so if some weather happens I’ll be hopping online of course.  Stay tuned!

Chief Meteorologist Mark Nelsen