no snow for you

Noon Tuesday… (LINK for app users)

Last night’s forecast worked out well for the most part.  There was a dusting of snow in spots, even down to sea level.  I picked up 1.5″ at 1,000′ at home, and of course nothing measurable fell in Portland.  This continues to be a snowless winter (officially) in Portland.  By the way, someone was complaining about that yesterday on Twitter.  You know we’ve had three consecutive winters with significant snow in Portland.  It would be nothing unusual if we get no snow the rest of the season.

Picture1

Today we’ve transitioned to just a few scattered showers with lots of sunbreaks.  GOES-17 image shows the breaks between the clouds

satellite

One part of the forecast I missed was a very thin layer of subfreezing arctic air that slipped into the eastern Columbia River Gorge last night.  Temps fell into the 20s as far west as Hood River.  In fact it was less than 1,000′ thick at that location; Parkdale stayed warmer than the lower valley.  I see some accidents along I-84 Hood River to The Dalles due to snow/ice on freeway.  There might be some brief thawing this afternoon with a brief westerly wind back in place for a few hours.

WHAT’S AHEAD?

There is a good chance we get no measurable snow in the next 48 hours for the vast majority of the metro area. 

Why?  Probably too “warm” for almost all of us.

Models have been pushing tomorrow’s strong weather system farther offshore and north the past two days.   We get our big snow/ice events in the metro area when cold air surges in from the Gorge and moisture runs over the top of that cold air.  With the system tomorrow now well forecast to be north of our latitude, we don’t get a significant push of cold air from the east.  Strong southerly wind, not just at the surface but a couple thousand feet overhead, overwhelms the cooling coming in from the east.  As of midday, there is only one model trying to produce snow west of the Cascades, and it has been the most unreliable lately.

So here’s what I think is most likely tomorrow through Thursday morning:

  • No snow at the coastline or anywhere south of the metro area.  That means no snow for Woodburn, Molalla, Salem, Albany etc…
  • During the afternoon hours tomorrow (with temps between 36-42 degrees) precipitation arrives.  It’ll probably be a rain/snow mix in the metro area.  Best chance for an all snow start would be north of the Columbia River (Clark County).  There is the slightest chance it sticks up there, but temperatures would have to fall 5 degrees or more.
  • It’s unlikely we get any sticking in the metro area from the Columbia River south.  It might even be tough to get sticking snow up on the West Hills, Mt. Scott, Chehalem Mtn.
  • Temperatures remain above freezing tomorrow night, unless rain showers end and a few spots clear out.  Then we’d get the usual “wet roads turn icy” in spots.  We saw that in Washington County this morning.
  • Thursday we’ll see scattered showers, although snow level remains relatively low, around 1,500′ in the afternoon…more Cascade and foothill snow!

MOST IMPORTANT:  We will know by midday tomorrow (if not earlier) for sure since we’ll see what temperatures/dewpoints are doing and if we’re actually getting any cold air out of the Gorge.  If we get to late morning and there’s no cold air pouring out of the west end of the Gorge then it’s over, even for Clark County.

Columbia River Gorge

It’ll be cold enough for snow tomorrow afternoon/night/Thursday AM east of Multnomah Falls, but there won’t be a ton of moisture to work with.  Expect 1-4″ snow from tomorrow afternoon (maybe not until late) through Thursday morning.  Western Gorge will warm quickly like the metro area.  Maybe just brief snow/freezing rain late tomorrow afternoon around Cape Horn, Corbett…etc.  It’ll depend on the temperature.

DISCUSSION

Only the #Sad GFS model is hanging on to snow chances tomorrow afternoon/evening. Zero to 6" in metro area, none south and up to 6" north.   The dependable ECMWF and WRF-GFS say forget it.  The reasoning is clear; I’ve never seen significant snow with 1) No cold arctic air in place + 2) isobar orientation forecast.  The low pressure center offshore is too far north.  There isn’t any strong pull of cold air from the east on all models except the GFS.  Check out ECMWF snow forecast

ecmwf_snowbymiddaythursday

And even better, the WRF-GFS.  When we’ve had marginal situations, there is at least a hint of SOMETHING across the lower elevations.

wrf_snowending4amThursday

Brian MacMillan and I were just discussing that we’ve never seen a significant snow event when this model doesn’t even have a hint of snow at the lower elevations.  Yes, even in the busted forecasts (surprise snow!) there has been some sort of hint.  You can see why in the surface map for 4pm (colors are temperature at ~2,500′) tomorrow, above freezing at that elevation plus very little cold wind coming through the Gorge.

slp.36.0000

Then check out the cross-section over Portland.  The “0” line is the freezing level.  Time runs the opposite of what you’d expect.  4am this morning right side, 4pm Friday afternoon left side.  Highlighted along the bottom in yellow is 1pm to 10pm tomorrow. Far too much mild southeasterly flow overhead to bring snow close to sea level.

Capture

To wrap it up…my gut feeling is we see light rain tomorrow afternoon/evening, maybe with some snowflakes mixed in.  But that’s it.  Hopefully the midday/evening runs of GFS model come back to reality and get rid of the snow chance for good.  Sorry kids!

I’ll be on TV starting at 4pm today…see you there.

Chief Meteorologist Mark Nelsen

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