The Weekend Is Here!

September 18, 2009

snapshotAh, for some reason it seemed like a long week and as soon as I finish THIS I get to go home.  But I can’t leave the weather faithful hanging without a few tidbits to chew on for the weekend can I?

Weak front moves through tonight and tomorrow morning; nothing too exciting here.  Then assuming we get some clearing tomorrow and Sunday night we should get pretty chilly.  It’s a cooler airmass both nights, so 38-44 in the coldest spots and 45-48 in the city seems about right.

Then the big offshore flow event kicks in Sunday night.  Several things stick out now:

1.  The usual waffling of models on the details continues, but the 00z GFS is just as hot as 24 hours ago.  As I mentioned last night, it’s probably a bit too warm.  But how about that closed 594dm upper level high over us Monday and Tuesday?  Whew!  That’s almost exactly the same orientation and heights we had in the August 1981 heat wave.  Obviously at the end of September we won’t hit 107.

2.  It’s going to be stronger offshore flow Monday and Tuesday than what we’ve seen so far this season.  The WRF-GFS has about 7 millibars easterly flow from near The Dalles to PDX during the day Monday.  That supports gusts to 50 mph at the west end of the Gorge…lots of blowing/scouring sand so not a good nudie day at Rooster Rock State Park!  Just kidding (partly), but we do have a wide variety of folks who read this blog.

3.  All models have the thermal trough at or well off the Coast.  This says temps will be just about the same at the beaches as inland.  I really like the the 100 degree forecast on the WRF-GFS meteogram for North Bend.  Even Newport shows 85.  Both days temps of 85-90 should be easy to achieve.  Too bad I can’t call in sick Monday…that would be a bit obvious.

4.  I upped Tuesday’s high to 95 based on the extremely high 850mb temps and perfect offshore flow.  I think 97 is possible at PDX if the wind isn’t averaging 20 mph.  I kept Monday at 90 because the heat wave is just getting going.  However Drew and I have discussed how we tend to under-forecast the first day of east-wind type heatwaves.  Wednesday is a total guess.  00z GFS says it stays really hot, but the ECMWF had a total loss of easterly flow, which brings us back into the 80s.

5.  In general, I think this is going to be a historic late-season hot spell…what a way to end the summer!  At least it’ll be in the 40’s and lower 50s at night though.

Chief Meteorologist – Mark Nelsen