Winter Storm Watch: Snow/Ice Likely Later Thursday

January 31, 2017

5pm Tuesday…

The NWS has issued a Winter Storm Watch for much of Western Oregon between the Coast/Cascade Ranges for Thursday and Friday.

markwarningswinter-wx

That means snow and/or freezing rain is POSSIBLE during this period but some of us may not get it, or get much of it.

We’re still two days away, but models have come into much better agreement on the general sequence of events the next 4 days:

HIGHLIGHTS

  • Wednesday will be colder with a very strong east wind spreading out across the metro area
  • Wednesday should be a dry day, or mainly dry.  Possibly a flurry/sprinkle in the afternoon that WILL NOT AFFECT ROADS.
  • Thursday AM should be dry as well for a clear AM commute.
  • At some point Thursday afternoon or evening, snow will spread north across Western Oregon and up into SW Washington.  Timing is TBD since we’re still 2 days away.
  • First guess (still 2 days away!) is 1-2″ snow for many of us in the western valleys before a transition to freezing rain by Friday AM.  If the transition takes longer?  More snow, less freezing rain.
  • During the day Friday, freezing rain is likely at times, but it’ll become confined to near the Columbia River Gorge (central/east Portland metro area) as temperatures rise above freezing in most other locations.
  • It’s possible that Friday afternoon many of us will see mainly wet roads south/west/north metro away from the Gorge.  This happened during the last two freezing rain events when we thought a large area would see freezing rain and instead it was confined to the central/east metro area.
  • A warming southerly wind late Friday night or early Saturday ends the freezing rain threat outside of the Gorge at that time.

ROADS/SCHOOLS

I see either Thursday evening and Friday morning commutes being a possible big issue anywhere in the valleys.  Friday could be a no-school day for many.  It could possibly still be very icy in parts of the metro area Friday evening too.  Again, we’ve got another 24-36 hours to fine-tune the forecast

 

WEATHER GEEK CHAT

Here we go again, hopefully for the last time this winter.  It was nice to see models come together pretty well on last night’s runs, and the same thing through this morning/midday runs too.  No model is showing any sort of significant snow now tomorrow through Thursday AM.  After checking several model’s thermal profile up through the atmosphere, I’m becoming convinced this will be more of a freezing rain “storm” than a snowstorm for most of us.  I think just about everything I checked shows that warming occurs overhead before sunrise Friday, so all of Friday’s precip will be in a liquid form.  That’s at least while falling.  Of course if surface temps are below freezing then you get the ice glazing which we’ve seen 3 times already this winter in the valleys!  Check out snow forecast from the GFS:

gfs_snow_fridaypm

The ECMWF

ecmwf_snow

and the WRF-GFS

wrf_snow_fridaypm

None show more than 2″ anywhere in the western valleys.  That’s due to warmer air coming in overhead…not “warm”, but warmer.  Then the next question has been “how cold will the air mass be that moves in on the east wind?”  I see several hints that it won’t be as cold as previous events in January.  The result could be that it’ll be easier to get temps above freezing over a larger area west of the Cascades during the daytime Friday, even with the easterly flow continuing through the Gorge.

I know we are all focused on snow and freezing rain, but I need to mention the strong wind tomorrow too.  Check out the cross-section from the WRF-GFS for the next 3 days.

kpdx-th

The solid wind barbs represent 50kts and each little barb is 10 kts.  So from tomorrow morning through Thursday evening easterly wind is forecast to exceed 60 mph over our heads…up around 2,000′.  Some of this strong wind will surface as gusts around 40-50 mph.  Of course this means we’ll see a few limbs/trees come down, especially across the east side of the metro area.  Since we’ve already seen wind this strong this winter I doubt we’ll see widespread power outages.  But regardless, it’s going to be a gray and chilly afternoon Wednesday.  It’ll be a big reminder that winter isn’t finished yet!

Chief Meteorologist Mark Nelsen