Windstorm Update: A Bit Less Confusion This Evening

December 9, 2014

We are less than 48 hours from what COULD be a significant wind event in our area and evening models are still in quite a bit of disagreement.

First, if you just want the basics:

  • Tonight’s storm moving onto the coastline will not bring strong wind into the valleys, but gusts to 70 mph are likely in the morning hours out there.
  • Storm #3 is still forecast to develop and bring gusty south wind to the entire region Thursday.
  • We unsure about the strength of the wind and the timing right now, but gusts to at least 40 mph are likely.
  • My best guess is we’ll see gusts 45-55 mph in the metro area Thursday midday or afternoon, similar to the October storm, maybe stronger…maybe.

What’s different since I wrote this morning’s post?  We have a new run of models in that show just a few changes.

1. The GFS (and, by extension, the UW WRF-GFS) has the low moving a little farther offshore.  It is also slower, bringing the wind in 3-5 hours later.  More like midday-early afternoon instead of morning.

2.  Gradients/wind on those two models are weaker as a result.  The WRF-GFS had shown a +8mb gradient EUG-PDX and now is +7.  The OTH-AST gradient is now +15mb instead of +19.  The wind gust forecast graphic was also weaker.  I wouldn’t go with gusts above 60 mph at SLE/EUG/PDX based on these two models.

3.  The 00z NAM and GEM are very similar.  Both showing a “baggy looking” low moving directly over Portland on the way up to Puget Sound.  This would give us a nice surge of 35-45 mph gusts Thursday afternoon, but not much stronger.  Here’s the 4pm Thursday view: gem

4.  The 00z ECMWF is a bit stronger than its earlier run and is now quite similar to the GFS except the track is right along the coast….10am Thursday:  ecmwf_18z

and 4pm:

ecmwf_00z

The ECMWF would suggest gusts around 50 mph Thursday afternoon west of the Cascades…maybe 50-60 if everything was just right (wrong).

We still have the 12z and 00z models tomorrow…hopefully they will firm things up a bit on track and intensity.

Chief Meteorologist Mark Nelsen


A Few Maps This Morning

December 9, 2014

11am Tuesday…

Morning model runs of the GFS and GEM both still show a very strong low pressure center racing up the coastline Thursday morning.   Check out the two GFS runs for 10am Thursday.  These are maps from WeatherBell.  The first is the “regular” model, the 2nd is the upgraded version which is still in testing mode and being run in parallel with the operational run for another month.

gfs

upgrade version:

gfd_upgrade

They are both similar, although the upgrade version is significantly deeper with the low and just slightly farther offshore.  Note the wind at 850mb (around 4-5,000′).  Near 100 mph southerly wind over our heads!  Then check out the GEM (Canadian global model):

cmc_mslp_uv10m_nw_9

A deeper low snuggled right up against Tillamook at the same time.  Wow…that’s a huge storm.  Now check out the morning ECMWF run.  First map from the same time (10am) as those above:

ecm10am

2nd map from 4pm.

ecm_4p

…much weaker and “baggier” with the low pressure center.  This would just be a windy afternoon with gusts in the 30-45 mph range.  So I’m not sold on a big windstorm Thursday morning until I see that Euro come around a bit more.

The UW’s WRF-GFS model, based on the GFS, produces a big windstorm for us.  Pressure jumps are strong behind the low…10 millibars in 3 hours at Eugene between 8-11am and a pressure gradient of 16 millibars Eugene-Olympia.  Combine that with a fast-moving low and the strong overhead wind; you’ve got gusts 50+ at least in the valley and Portland.

More after the evening runs come out.  Hopefully they will pull together a bit or “cancel” a windstorm.

Chief Meteorologist Mark Nelsen