Is It Going To Snow In the Lowlands? No

November 22, 2015

9pm Sunday…

The most useful indicator for snow chances the Portland Metro Area the next few days will be the web site  http://isitsnowinginpdx.com/  This is one of my favorite sites; which 364.5 days of the year displays this:

 

Capture.PNG

Looking for a day off work or school Tuesday…it’s pretty unlikely that’s going to happen.  The colder models have slowly been coming around to the slightly warmer ECMWF and GEM models for Monday night and Tuesday so…

  • Steady rain develops in western Oregon/Washington Monday evening.
  • It turns to cold showers daybreak Tuesday morning
  • Sticking snow at that time reaches the lowest point around 1,500′.  That’s the top of the Coast Range summits, Welches area, and the very top of Bald Peak possibly.
  • Anywhere else in the hills could see a “sloppy mix” of snow/rain showers around daybreak but no accumulation with temps above freezing.
  • The rest of us just see a few light & chilly showers tapering off through the day with mainly dry conditions by Tuesday afternoon
  • Traffic in the lower elevations will not be affected by snow this week; continue with your usual and customary Thanksgiving Preps!

I do expect 5-10″ in the Cascade passes by Tuesday midday, which means snowy driving through at least midday Wednesday.  Then the snow will gradually work off the roadways.

Why am I so negative about low elevation snow?  Model 850mb temps have ever so slowly risen to around -4 to -5 with the precipitation Tuesday morning.  That’s not lowland snow material.  We need -7 with onshore flow, and it doesn’t help that our ocean is running several degrees above normal.  The air will be coming in off that ocean Monday night and Tuesday morning.  I notice the WRF-GFS maps are looking less and less snowy…this evenings’s run:

or_snow72.84.0000

and our RPM evening run:

RPM_SNOW_00z

Beyond that we should just be dry and chilly (but sunny) Wednesday through most of the holiday weekend…very nice.

Chief Meteorologist Mark Nelsen