Major Coastal Wind Storm Arriving Next Few Hours; Possible Snow in Valleys Too

March 11, 2012

I’ve been a bit busy this weekend, but keeping an eye on the maps, but it’s midnight Sunday and time to check in…

Two main items I’m seeing right now:

1. The strongest coastal storm (of the winter?) we’ve seen in quite a while is bearing down right now.  A deep low pressure center is “bombing out” as we say out around 130W, maybe 200 miles offshore of Tillamook.  It’s headed northeast for central to northern Vancouver Island.

2. All mesoscale models (which are getting pretty good at the details) are hinting at unusually low snow levels for mid March between 11pm and 5am tomorrow night/Tuesday morning.

First, the coastal storm…wow!  Very impressive.  Recent model runs have it slightly closer to us as it races offshore to our west overnight, here’s the WRF-GFS forecast for 5am:

Look at those isobars packed along the Washington and Oregon Coast.  The NWS has a Hurricane Force Wind Warning for the offshore waters (not on land), but I still expect gusts 75-95 mph at the windy spots between 3am-10am.  Very impressive even if it was mid winter, but it’s mid-March.  GENERALLY this setup doesn’t give us real strong wind here in the western valleys because we want the isobars to be oriented a bit more east-west across the valley.  When it does that the wind just races up the valley straight south to north.  BUT, cross-sections show 80-90 mph wind directly over Salem and Portland at 5,000′, plus 60 mph wind just a couple thousand feet off the ground from daybreak to noon or so tomorrow.  It’s possible that some of that stronger wind will mix down and we get gusts to 50 mph in the valleys, especially south of the metro area where a light east wind out of the Gorge won’t slow down the southerly wind as much.

Either way, a major windstorm on the Coast and gusts 40-50 mph in the Valleys is quite an event for March.

Lots of rain all day tomorrow as the cold front lingers overhead.  Then it SLOWLY slips south tomorrow evening and tomorrow night.  This is where the forecast gets tricky in the lower elevations west of the Cascades.  As the steady precipitation continues tomorrow evening, after 8pm or so, the mild south and southwest wind goes light.  That plus colder air arriving aloft helps lower the snow level close to the surface.  I’ve been surprised at how persistent the RPM, WRF-GFS, and MM5-NAM have been at trying to bring the snow level right down to “the deck” from around 11pm-5am.  Our RPM seems a bit aggressive with widespread 1-3″ in the lowest elevations, but even the WRF-GFS shows a trace just about everywhere.   Depending on the model, there appears to be plenty of precipitation during this period, that, combined with marginal 850mb temps only around -5 or -6 could lead to quite a dumping in the foothills of the Cascades.  It’s a strange situation, but I’ve seen it happen before.  It’s also a “one shot deal” in that once we get to daybreak Tuesday it’s over for sticking snow; after all, it is mid March and even in the coldest patterns like this afternoons are into the 40s.

Here is our RPM:

And the WRF-GFS, I think it’s a bit more reliable…showing nothing to 2″ even on the hills in the Valley:

So this is what I’m thinking for sometime between 11pm Monday night and 7am Tuesday:
Lowest elevations from Vancouver to Eugene:  Zero to 1″ very wet snowfall possible.
Hills up around 1,000′:  2″ possible, except 2-4″ up against the Cascades at this elevation
1,500’+:  6-10″ likely…a big March snow dump!

Tuesday morning commute?  Probably fine in the lowest elevations, but could be a sloppy mess in the hills.

More stormy weather later this week and tons of snow in the Cascades.

And here is the 00z GFS ensemble chart…a hint of more reasonable weather about 8 days from now:

 

Chief Meteorologist Mark Nelsen