scary offshore flow

5:30pm Sunday…

Apparently there is some sort of important football game on FOX12 right now, so no 5pm show this evening…good time for a blog post!  And joking about the big game of course.  I’ll be on live TV with fresh model info at 8/9pm on FOX12Plus and 10/11pm on 12.  See you then.

BIG PICTURE:  Some, but not all of us, will see some white on the ground within the next 48 hours.  The forecasts below apply to all areas from Longview to Albany in the western valleys of SW Washington/Oregon.  Including Portland, Vancouver, Salem of course.

THIS EVENING / TONIGHT

  1. Showers mix with snow as temperatures drop
  2. ANYONE could see a dusting on the barkdust I suppose.  But for most of us in the lowest elevations/cities it won’t be quite cold enough for sticking snow and/or the showers will be too light to drop the snow level much below 1,000′.
  3. We’re talking off/on showers tonight.  I don’t think I’ve ever seen widespread snowfall in this setup.

MONDAY A.M. COMMUTE

NOTHING TO DUSTING IN THE LOWLANDS.  UP TO 1″ SNOWFALL NEAR 1,000′,  2″ UP AROUND 1,500′

  • Since it’s showery, many of us will wake up to nothing or just the “white on barkdust” stuff at best.
  • Some school delays are likely in the highest areas (top of West Hills?, northern Clark County, Cowlitz County?).  Rest of the kids can plan on normal school hours
  • Some roads will be slushy or have light snow on them at/above 1,000′
  • MAIN HIGHWAYS/FREEWAYS WILL BE CLEAR FOR A.M. COMMUTE
  • There is a small chance a wet road freezes somewhere tonight if a local temperature drops to freezing.  Keep a close eye on your car thermometer tomorrow morning!

Snow Cold Look Ahead Forecast 2


DAYTIME & EARLY EVENING MONDAY

  • Continue your normal Monday life…
  • Roads/highways all clear with high temp 38-40 in afternoon, slushy snow left on roads up near/above 1,000′
  • Scattered showers change to steady rain/snow mix at times, especially Portland south.  But little/no sticking snow below 1,000′

MONDAY NIGHT THROUGH TUESDAY AM COMMUTE

  1. BETTER CHANCE FOR LOWLAND DUSTING OR LIGHT ACCUMULATION, especially from Portland south to Eugene.   Cooler temps + showers continuing = better for snow.
  2. First guess (will update tomorrow of course) is a dusting to 2″ on the ground at the lowest elevations for Tuesday AM commute.  Mainly south and east of Portland (more moisture, slightly higher elevations = better chance for sticking snow).  Salem could end up with an inch or two Tuesday morning, but nothing around Vancouver or downtown Portland for example.

WEDNESDAY

I still think we have some sort of larger “snow event” coming for some part of the western valleys of Oregon & SW Washington, but details are very uncertain.  Will it just be a 12 hour snowfall with only 1-2″ and then we warm up?  Or a 24 hour long fiasco with the metro area frozen under several inches Wednesday afternoon through sometime Thursday?  We don’t know yet; but it’s still three days away.


COLUMBIA RIVER GORGE

No cold east wind through the Gorge until Tuesday night so I-84 should be in good shape most of that time.  Just 1-2″ each 24 hours above river level.  But that very cold and strong east wind arrives Wednesday!  Prepare for some sort of snow/ice event later Wednesday-Friday, especially central/east part

OREGON & SW WASHINGTON COAST

Cold showers tonight through Tuesday midday.  At any time a vigorous shower could dump hail or snow, even down to the beaches.  We could briefly see “white sandy beaches”.   But highs each afternoon in the upper 30s would melt that quickly during the day.

Trace -2″ possible anywhere along the beaches if a heavy shower passes by.  That’s either tonight or tomorrow night.


DISCUSSION

The forecast for tonight through tomorrow afternoon is simple.  It’s the cold onshore flow weather pattern.  Arctic air has moved out over the ocean, picked up moisture, and that comes inland as cold rain or snow showers.  This pattern almost never produces notable lowland snow.  But I have seen it bring an inch or two around Kelso/Longview since it tends to be a bit wetter up there.  And anywhere with some elevation helps.  Notice I don’t specifically mention 500′ or 1,000′ much.  That’s because there is no specific elevation where it does/doesn’t snow.  Heavy showers can drag sticking snow to sea level, but if only light showers pass over a hill at 1,200′ there may be no snow sticking even up there!  850mb temps tomorrow are marginal for lowland snow anyway.  -6 to -7 often doesn’t get snow to sea level with onshore flow.   Models agree, forecasting essentially nothing through midday tomorrow:

nam_snow_ending 18z

Tomorrow night is a bit tricker.  That surface low is still expected to move right across central Oregon, spreading steady precipitation across the Willamette Valley.   The arctic front, boundary of very cold continental air, will be up around Kelso/Longview and down to around The Dalles east of the Cascades.  No model forecasts it to slide farther south.  Because of that, the ECMWF thinks it’ll be too warm for much snowfall tomorrow evening/night even under that steady precip.  WRF-GFS thinks it’ll be significantly colder (it’s based on what seems to be a cold-biased GFS).  My gut feeling is we may not see much snowfall tomorrow night and Tuesday, but I put it in the forecast based on an abundance of caution.   You see the lack of snow in the Euro forecast 4pm Monday to 4pm Tuesday.  This 18z run backed off more than the 12z

ecmwf-deterministic-portland-snow_24hr-9046400

Then the “aggressively snowy” WRF-GFS.  We’ll see if this goes away in three hours when evening run comes in.

wrf_snowfallmondaypmtotuesdaypm

Finally, what to do about Wednesday/Thursday?  It’s still three days away, but there are doubts whether it’s really going to be a major player or not.  The GEM and ECMWF are now saying we get brief easterly flow in the metro area then transition to southerly surface wind within 12 hours or so.  That’s because they are swinging the deep low far north offshore.  You need to keep the surface low west or southwest of PDX to keep the cold Gorge wind pumping air into the western valleys of Oregon & SW Washington.  But the GFS is a perfect setup for a major snow event.  Huge easterly flow through the Gorge and deep low to our southwest.  This is Wednesday afternoon

wrf_sfc_4pmWed

A neat tool nowadays is to compare ensemble surface low pressure locations.  All 21 members from the GFS; general agreement low is southwest of us Thursday 4am.  Snowstorm Wednesday PM through Thursday midday in this case.

gfs_lowlocations18z

Yet the 51 members of the 18z ECMWF say forget it…we’re outta here and heading north!  All of 1-2″ snow is done in Portland by Thursday morning in this case.

ecmwf_lowlocations18z

That’s plenty for now.  Enjoy watching the snowflakes fall the next 24 hours…at least we’ll all see some in the air!

Chief Meteorologist Mark Nelsen

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