Snow In Lowlands? An Update

The snow rumors are just getting going today, and they should be going crazy the next 2-3 days. A bit amusing since we have 3-4 days of beautiful sunshine ahead! I covered all that in the previous post, so let’s move on.
For those just checking in wanting the basics here you are:

1. Our best chance of sticking snow to the lowest elevations (in the cities) this winter so far arrives Sunday and continues through Tuesday, possibly a bit longer.
2. The possibility of an inch of snow in the city of Portland has increased a bit since last night…I give it a 50/50 at this time.
3. Those of you in the hills (1,000’+) should get at least some snow, possibly quite a bit (6″+) during this period.  First chance is probably Sunday morning…we’ll fine tune the timing later.
4. Finally, the Cascades should see quite a bit of snow next week.
5. As of now, I don’t see any “arctic blast” or major snow/ice storm, we’re talking the heavy, wet, 32 degree snow.

Okay, so what’s changed?  The news snow-train has left the station…

The GFS has come into line with the ECMWF the past 24 hours, and all models seem to be in agreement for an “onshore flow” low elevation snow pattern. I hate these. This pattern has at least a light or even moderate southerly wind up the Valley the whole time, so some spots can get 2″ as a batch of showers moves through and other spots nothing.  The new GFS was signficantly wetter Monday and Tuesday as well.  It has been lowering upper-level heights the past few runs, thus the cooler temps.

Tuesday and beyond it’s quite the battle between cold air to the north and westerly flow pushing in from the west.  For now, I don’t see a setup for an easterly-flow type snow situation, but only a shift south in the models would bring surface low pressure systems in to our south, possibly setting up a big snow event.  Something to keep an eye on.  I notice the 00z GFS ensembles are almost all a bit colder than the operational GFS Tuesday-Thursday.  Could be a sign that the heights will be even a bit lower, along with those lows a bit farther south…we’ll see:

Anyway, COULD be fun times ahead, or we might just get some marginal snow Sunday-Monday.  Of course even that will be far better than anything else we’ve seen lately.

Chief Meteorologist Mark Nelsen

Cold, Sun, & Wind Arrives Tomorrow

We’re about to see a somewhat dramatic shift in our weather pattern tomorrow through Friday or Saturday.  Say hello to sun, wind, and dry skin.  Say goodbye to fog, rain, and cloud cover.

Quite a surge of cooler and very dry air is moving through northern Washington this afternoon.  The dew point, a measure of the amount of moisture in the air, is falling like a rock in those places.  We’re already significantly drier here in the metro area this evening.  But Bellingham has dropped from 34 to 24 in just 3 hours, Spokane’s has gone from 30 to 12 in just 4 hours as the wind switched from west to north. 

All this dry air is headed down here into Oregon, so “skin-wise”, it’ll be the driest conditions we’ve seen so far this winter.  As you might guess, this means fog will only be patchy tomorrow west of the Cascades.

As the cold/dry air surges south through Eastern Washington, a very strong surface high pressure area develops over there, similar to a bathtub filling with heavy & dense water.  The only “drain” at sea level is the Columbia River Gorge; all that cold air will begin surging through the Gorge tonight and it’ll continue through Friday or Saturday.  Prepare for 3-4 days of strong easterly wind if you live at the west end of the Gorge.  Probably the coldest we’ve seen so far this year under sunny skies.  Here’s what we call a “cross-section” of the atmosphere for the next 3 days from the WRF-GFS model (UW) over Troutdale:

A few items:  The colors are relative humidity, clear is less than 50%.  Time goes from RIGHT TO LEFT.  The 10/12 refers to 4am this morning (Tuesday).  11/00 is 4pm today (right now), and 11/12 is 4am tomorrow, the 11th.  The far left side is Friday afternoon.  The bottom of the graphi is sea level and the top is 10,000 ft.  Notice the quick change as easterly flow commences right around 7pm in the atmosphere overhead, then it surfaces by daybreak out in the eastern metro.  By tomorrow midday, 45 kt easterly wind is just a thousand feet or so above the surface.  It’s going to be a big day out at Vista House.  Gusts in the western Gorge will be up around 60mph, with the usual 90 mph (or more) at the “Keely Chalmers Memorial Railing”.   This time around it’ll probably only be 35-38 degrees up there midday instead of 45-48.  Brrr!  I can’t make it this time around since I have a haircut at 11am…too bad.

The chart clearly shows bone-dry and clear through Friday afternoon.  A few high clouds may show up, but they will be higher than 10,000′, thus they don’t show up here.

More on the extended forecast on a following post.

Chief Meteorologist Mark Nelsen