Heat and Lightning

September 7, 2011

A cluster of thunderstorms developed around Crater Lake this evening and has now pushed up into eastern Lane County.  This is associated with a small upper-level disturbance moving north around the west side of the upper-level high.  Our RPM model shows the cluster moving up to around Mt. Hood as it swings north and then east between now and daybreak.  Hopefully some flashes to the east later tonight for us weather weenies;  but it’s really bad fire weather!

After today we now know that we need easterly wind to spread out into at least part of the Metro area to maximize the heating in early September.  The top of the KPTV Tower (at 1,900′) made it to 91 degrees today, so we could easily have hit 100 with the same air mass in early August.  But the lowest levels never totally mixed out.  Tomorrow and Friday we’ll have no easterly flow even through the Gorge, so a slightly cooler air mass should drop our high temps a few degrees.  Plus dewpoints have climbed a bit as well.

We’re back in the weak offshore flow at the surface Saturday and Sunday, but nothing better than what we had today.   That IS good for fire conditions; the lack of gusty easterly wind today kept all the main fires from really exploding or making big runs like the Dollar Lake fire did last Saturday. 

 This isn’t a typical September east wind pattern where a cool high slides down over the Rockies.  Instead it’s an amorphous blob of hot air with no major air movement any direction.  The upper level high breaks down a bit next week, then some models have it coming back about 9-10 days from now.  So no major changes in sight…we’ll easily go through the first half of September with no rain.

Chief Meteorologist Mark Nelsen