Unusually Strong East Wind Thursday

September 10, 2014

We’ll see a surprisingly strong east wind event here in the Portland Metro Area the next 24 hours; at least for early fall.  In fact the NWS has issued a wind advisory

MarkWarnings_High Wind

The Highlights:

  • Gusty east wind arrives in the western Gorge and foothills of the Cascades after midnight.  Those of you in those areas may wake up to trees blowing around, or your lawn furniture flying.  This includes Battle Ground, Hockinson, Sandy, Welches, Estacada, Boring etc…
  • The wind will spread across the rest of the metro area around sunrise or soon after
  • Peak gusts are likely between sunrise and 3pm
  • 55-65 mph in the western Gorge
  • 40-45 mph eastern metro area (east of I-205) and foothill locations mentioned above
  • 30-35 mph anywhere else in the orange area
  • These speeds are more typical for late fall, not the 11th of September.  So we’ll probably see scattered power outages, some fruit ripped off trees, cornstalks flattened in the windy areas, and a few trees down.
  • The rest of the lower elevations, coastline, & eastern Oregon will just be breezy, nothing too wild.

Details:

Cold high pressure is sliding south through the Rockies, bringing the first snow of the season for those areas.  The air spreading out from that high pressure is pushing northeast wind across the Pacific Northwest right now.  The easterly wind has made it into the east end of the Columbia River Gorge at 6pm.

I’m impressed by the strength of the pressure gradient and winds just above the surface tomorrow.  I don’t think I’ve ever seen a 7-8 millibar gradient through the Gorge in early September.  That’s what the UW WRF-GFS model is forecasting.

Take a look at the cross-section from the WRF-GFS:  

New Scene

You read it in reverse time-wise.  Time runs along the bottom, from this morning at 5am on the right side to Saturday afternoon at 5pm on the left side.  The bottom is here at the surface, and the 700 up top is around 10,000′ elevation.   The green colors are relative humidity above 70%.  Obviously after midday today the atmosphere was going to be quite dry…no clouds in sight through the weekend!  The wind barbs are a bit simpler, they flow with the wind direction.  Each barb is 10 kts and the triangle means 50 kts.  You can see the rapid increase in wind overhead tonight in the area I’ve circled.  By 5-8am Thursday winds are blowing 50-60 mph several thousand feet above the ground here in the metro area;  I’ve never seen the 50 knot barbs over us before Halloween!  The result is the possibility of damaging wind in spots tomorrow, especially since we don’t usually have east wind this strong while leaves are on the trees.

The real strong stuff only sticks around 10-12 hours, but then dry easterly flow (more like last week’s) continues through next Monday.  

There is one bonus…if your power goes out for a few hours when it’s sunny and 75 degrees, is that really such a big deal?  Better than when it’s icy and 25 degrees!

Chief Meteorologist Mark Nelsen