Coldest and Strongest East Wind Of Season Next 24 Hours

Brrr!  Real winter is here in the Portland Metro Area and Gorge this evening and some years it doesn’t get any colder than this!  Here are the highlights:

• East wind is already gusting 35-45 mph in the eastern suburbs and 60-70 mph in the Gorge, it’ll increase dramatically overnight and continue very strong through Thursday morning.
• The next 36 hours we’ll see peak gusts 50-55 mph near the mouth of the Gorge well east of I-205, and gusts to 40 mph as far into the metro area as I-205.  Same 40 mph gusts on the west slopes of the West Hills where the wind rolls down off the ridges.  It’ll be lighter (just breezy) all other parts of the metro area.
• Keep in mind Vista House is closed still to vehicle access, but you can walk down there.  You must park at the closure at the junction of Larch Mtn. Road and walk about 1/2 mile down the road.  Windchill out there is about 10 degrees.
• We only hit 40 today at PDX under totally sunny skies!  Not a record cold day by any means (only 5 below average), but add in the wind on the eastside and it felt cold.  Troutdale’s windchill reading stayed in the 20s all day with a real high of 38.  Temperatures will be similar or slightly colder Wednesday.
• The northern Willamette Valley and SW Washington may see spots of freezing rain or ice pellets Thursday morning; timing and amount of moisture are still very much up in the air.

Forecast the next 24 hours is pretty straightforward…east wind and cold.

Pressure gradient is really ramping up through the Gorge this afternoon/evening as expected.  At 7am the TTD-DLS gradient was 6.1 mb, now it’s up to 8.7, likely headed for 10-12 millibars by sometime midday tomorrow.  East wind has ramped up as well, gusting to 79 mph midday today.   Gusts around 80 mph just 1 foot off the side of the building there generally means gusts 95-100 mph on the favored railing/steps.  So tomorrow will be a HUGE day up there for wind 100+ mph wind gusts easily.

The airmass coming through the Gorge appears to be almost exactly the same temperature as 24 hours ago, so I don’t foresee temperatures much cooler (if any) tomorrow for highs.

The air coming through the Gorge has dried out a bit today, dewpoints are around 20-25 degrees in the windy parts of the metro area.  That shouldn’t change much in the next 36 hours (through Thursday morning).

That sets us up for some possible interesting weather early Thursday morning…all models have a very weak upper level wave moving right overhead along with a slug of clouds and a few hours or precipitation.  Several questions with this one:

1. How much precipitation?  Our RPM is real light with less than .10″, the WRF-GFS is similar, although slightly wetter.  The NAM is mostly dry (it was with yesterday’s system too!). 

2. When will it arrive?  Seems to be between 7-10am on the main models I trust, the ECMWF has been a little slower, more like midday to early afternoon.    Timing is perfect (if you want frozen precipitation) after a clear and cold night, frozen ground etc…

3. Precipitation type?  Oh, that’s a tough one.  Either snow, ice pellets, or freezing rain is possible.  Or even only rain in some of the east wind spots that only dip to 33-34 after evaporative cooling?  Big question mark on this one.  Soundings would seem to indicate only freezing rain is possible west of the Cascades since temperatures will be well above freezing above 1,500 to 4,000′.   So this might just be a “brief spots of patchy freezing rain” for 2 hours Thursday morning event.  We’ll see.  No model is showing signficant precipitation, but remember it only takes about 5-10 minutes of freezing rain to make a road a temporary ice rink!

Long Range Maps (3-15 days out):  Ewww!  Not good if you want exciting weather.  The GENERAL pattern is some split flow at first, then ONE cold trough about 8 days from now for at least foothill snow (maybe lower), then upper level ridging seems to want to develop again overhead or slightly offshore.  If you want an arctic blast and/or snow, you want the ridging a bit farther west.

Take a look at the 12z GFS and ECMWF 500mb ensemble mean maps for 14 days from now showing a very similar pattern:

Here is the 12z ECMWF 850mb ensemble chart:

It shows cooler than average temps after about Day 10 with that ridge slightly offshore.

Chief Meteorologist Mark Nelsen