Is There Going to Be a Wind Storm Thursday? Maybe

December 8, 2014

9:30pm…

The next 3 days we have a very active weather pattern with warm & windy systems moving across the Pacific Northwest.  The source region of the air is well to our south/southwest, so snow levels will be around 7-8,000 feet the next two days.  Forget about ski areas making a big opening this weekend.  This is our forecast for the next 7 days up on Mt. Hood. MarkSnow_MtHoodFcst_2013  Not good.  HOPEFULLY we don’t get much ridging next week and can squeeze out a couple of feet of snow at some point to at least get some sort of skiing open for Christmas Break.  The ECMWF model is not very hopeful, the GFS a bit wetter.  We’ll see.

Let’s talk about the stormier weather the next few days.  We have one system moving onshore later tonight.  That should give a burst of southerly wind along the coastline later tonight through early tomorrow morning.  A good surge of rain too.

A second system moves in on Wednesday.  This one is stronger with wind gusts along the coastline more likely into the 70 mph range…this is where ears perk up along the coast.  Gusts to 70 or higher are what start causing damage.  We’ll get some southerly wind in the valley again, but neither or these two systems are right for giving strong wind inland.  The pressure gradient is a bit too “southeasterly”.  For strong wind in the valley, you want the pressure isobars oriented as close to east-west as possible.  It doesn’t do that with these next two systems.  More rain arrives Wednesday afternoon, and I expect a good 2-3″ widespread across the region west of the Cascades by Thursday.  This isn’t enough to cause flooding, but definitely enough to remind us we are in the middle of the wet season.

By the way, the warm airmass and southerly wind means very warm temps…I think late tonight or before noon tomorrow the western valleys of Oregon/SW Washington may see temps right around 60 degrees.

Now on the really interesting stuff…Thursday.

Several models (notably the GFS) are showing a near-perfect windstorm setup for the Willamette Valley on that day.  The GFS shows (for the past couple of runs) a surface low pressure center deepening rapidly west of Eureka/Brookings and then tracking north very quickly along the coast.  This is how the latest run looks at 10am Thursday:

gfs_10am

notice the surface low is just north of Astoria.  What you don’t see here is the incredibly fast movement…about 350 miles from off Brookings to far NW Washington in just 10 hours or so.  That fast movement means pressures fall and rise very quickly as it passes by.  This speed can really add to the effect of the south wind rushing in behind the low as it moves north.  This track is similar to the OMSI Weather Meeting Storm on October 25th.  I just made up that name…it’s not official.

Our RPM model and the UW-WRF model also show a strong low tracking north too.  Not a surprise since they are based on the GFS model.    Check out the crazy WRF-GFS with major windstorm material for our area.  It produces gusts 70mph in the north Willamette Valley.

wrf_10am

So why not forecast a big windstorm?  Two reasons.  One is the upper-level pattern.  I don’t like the “splitty” look to the large upper-level trough to the west and it seems odd that models are deepening a low pressure center so rapidly in that general environment.  The other reason?  Check out the 00z GEM, 12z ECMWF, and 00z NAM…two of those are saying  “what storm?  I can’t even find a low pressure center!”

gem_10am

12zecm_10am

nam_10am

We’ll get a new ECMWF model for this period just after 10pm.  If it still says CAN’T FIND A LOW PRESSURE center I’ll sleep just fine tonight.  If suddenly it’s showing a deepening low coming up the coastline…things are going to get exciting real quick.

10:15pm update…ECMWF just came in.

ecm_10am

It now has a closed low tracking quickly north like the other models.  This says the central pressure is just under 988 mb, but the WeatherBell version is down around 980mb.  There are two key differences…the low is filling after it gets near the central Oregon Coast, and the path takes it inland around Astoria.  Then northeast to near Seattle.  This track (with a similar strength low) would give our area stronger wind than a track offshore.  On to the next run of models to see if they stay with the idea.

Chief Meteorologist Mark Nelsen