How Hot?

July 17, 2006

The big story this week of course will be the heat wave at the end of the week.

First, a pretty good onshore push is in progress this evening.  Portland to The Dalles pressure gradient is up from 3.2 mb. yesterday evening to 5.7 now.  Looks like wind on the river from Hood RIver to The Dalles are probably gusting over 50 mph, since DLS airport gusted to 48 mph at 5pm.  It has a lighter west wind than the big windsurfing spots downriver (Rowena/Doug’s Beach/Swell City).  It is a northwesterly push (as opposed to the strong pushes that come up from the SW), which usually doesn’t give us a ton of marine clouds.
Thinner marine clouds Wednesday allow temps to rise back into the lower 80’s…that should be the last day below 90 for many days.
12z/18z GFS, 12z ECMWF & Extended MM5 from UW all show a very strong 595 dm 500mb ridge developing directly over or just north of Oregon Friday-Sunday.   Then it weakens, but summer warmth continues Monday and beyond.  So the question is how hot?  You’ve all discussed your theories (and will for the next 4 days I suppose), so here are my thoughts.
I checked the 1981 & 1965 heat wave maps (Surface, 500mb heights, 850mb temps) and found that the pattern is very similar to the forecast pattern. 
– 500mb heights are the same. 
– To get above 101 or so we need some easterly flow through the Gorge, maybe briefly making it to PDX (as in June).  Both of those old heat waves had it and that’s in the works for Friday-Saturday.  Sunday is the calm wind day before we turn onshore for Monday. 
– 850mb forecast temps are the same as in the other two heat waves.  ECMWF has a crazy 28 deg. C on Saturday afternoon! 
     So technically there is no reason we can’t get to 105 or higher.  I went for 105 both weekend days on tonight’s forecast, which I’ve never forecast.  I’ll revise upward the next few days if the maps remain the same.
Ever since I started my career here in 1991, I’ve wondered when/if we would see a repeat the 1981 heat wave, so maybe this is the year?