Lots of Sun Ahead; Thanks to The East Wind

December 7, 2011

I’m at home sick this evening, a decent cold and I sound really strange, which is bad in this business.  Since I’m  wide awake after sleeping a decent chunk of the past 6 hours,  I figure now is a good time to comment on the weather situation. 

Most interesting at 10pm is the fact that at first glance there shouldn’t be anything to talk about for the overnight hours; we’re still socked in with a low cloud deck west of the Cascades and one would think it’ll just stay that way overnight.  Maybe forecst a low of 35 at PDX.  But that seems unlikely for many of us; we may wake up to a frosty/foggy morning and just plain sunny right near the Gorge. 

Here’s why:  You probably noticed the low clouds/fog last night lifted up and the inversion deepened a bit.  That actually helped warm temps up a bit late last night so no morning commute issues.  Now the bottom of the low clouds are between 1,500 & 2,000′ in the metro area this evening as they have lifted further.  At the same time easterly flow is forecast to develop (and appears to be doing so right now) tonight from 1,500′ all the way up to around 5,000′, drying out the atmosphere quickly.  That’s not just from the Gorge, but widespread across NW Oregon and SW Washington.  The WRF-GFS shows 15-20kts at 2,000′ by 1:00am.  This wipes out the current low cloud layer over us.  In fact I just checked outside here in Corbett and it is mostly clear after totally cloudy all day.

So the cloud layer disappears for almost all of us the next few hours, yet we have a moist and chilly low level airmass below that; perfect for a cold, frosty, and eventually foggy night.  It’s as if we’re going to “start over” with a new fog layer at the lowest elevations by tomorrow morning.  The trickier part is how do most of us get rid of the fog?  Near the Gorge it’ll be easy…4-6 mb. easterly gradient by midday tomorrow; a slower breakout for the west and south sides of the metro area. 

Tomorrow night and Friday the east wind really starts cranking, probably the strongest we’ve seen so far this season.  Check out the 22 degree temp over The Dalles at 2,000′ by Friday morning, yet around 46 at the same elevation right over the Portland Metro Area!  That is a deep, chilly, airmass that develops eastside (over 3,000′ deep), flows through the Gorge, and blasts out the west end.  It’s the first time this season we’ll see a cold airmass develop eastside in the Columbia Basin with a very warm airmass up above 2,000′ at the west end of the Gorge.  As a result we should all see sun Friday along with gusts around 40-45 mph at Troutdale/Gresham and 80-90mph at Vista House.   It won’t last long as the overall gradient reverses Saturday with an upper-level shortwave approaching.

Chief Meteorologist Mark Nelsen