Tough Forecast: Will There Be A Wind Storm Saturday?

October 24, 2014

11pm Friday…

The chance of strong wind in the Willamette Valley and Metro area Saturday has dramatically increased this evening, but it’s definitely not a “done deal”.  Here’s the latest:

  • Models have come together with MOST of them showing a surface low tracking north along the coastline quickly tomorrow afternoon.
  • Air rushes in the south side of the low as it moves north quickly, thus a gusty south wind behind it.
  • My latest thinking is wind gusts 40-50 mph possible from Portland down to Eugene.
  • Two models imply the wind could be significantly stronger in the central valley….gusts 60+.  If so, that would be the strongest Willamette Valley windstorm in years.
  • Prepare for power outages and some downed trees if either scenario occurs.
  • Whatever happens will be done after just 2-4 hours, then back to the usual showers and breezes through Sunday.
  • As of 11pm, there are no watches/warnings/advisories from the NWS and no media freak out.  It’s a bit weird.  We’ll see if that changes in the next 12 hours.

So what has changed?

This evening’s model runs have mostly all (ECMWF comes out in 20 minutes) converged on a low center tracking in the perfect path…right along the coastline and then inland over SW Washington.  That’s the GFS, NAM, and GEM.

They also don’t show the surface low “filling”, or pressure rising within the low, like they did this morning and on earlier runs. Plus the pressure is lower on the earlier runs.  What caught my eye this evening is the very strong wind field over us as the isobars line up with the Willamette Valley.  Take a look at the WRF-GFS sounding over Portland…50kts just off the surface up to around 70kts at 850mb (~4,500′)

wrf_2pm_sounding

We don’t often see the wind field at all elevations aligned directly south to north at the same time the pressure gradient at the surface jumps up from Eugene to Portland.  The WRF-GFS goes nuts, showing 55kt wind gusts (around 65 mph) in the central valley.  Other than earlier this week, I’ve never seen this model show such strong wind in that area.

wrf_2pm_windgust

The NAM is not quite as strong, although it still shows gusts around 50 mph in the valley.  Models still don’t show the low deepening as it moves north; that would be a major windstorm.

Hmmm, a few other hints.  moswind  The 00z GFS MOS (model output statistics) shows an unusually high south wind averaging 24 mph at 2pm as well.  We don’t see it go that high very often.  The Salem value is 34!  That’s average speed.

I should point out this may be a last-minute screwup in modeling.  Our RPM (not always a stellar performer) still has just a baggy-looking low pressure trough with wind gusts maybe 30 mph…snooze.

ECMWF UPDATE 11:15 PM  Whoa!  The Euro just came in with the exact same track and strength. It’s even faster (good if you want strong wind) and forecasts 18 millibars pressure gradient late afternoon from Eugene to Olympia.  That’s significant windstorm material.  It also forecasts 50kt (around 60mph) wind gusts in the valley. ecmwf_windstorm  So all major models are showing the same thing right now…confidence is even higher.

I’ll be up early tomorrow morning before the OMSI meeting (at 10am sharp!) checking things out.

Chief Meteorologist Mark Nelsen