Today is the Day; The Heat Is On!

August 20, 2011

Everything has fallen into place this morning for our first 90 degree (or plus) day in the interior of Western Oregon and parts of Western Washington too.  Skies are clear, and the atmosphere has warmed dramatically the past 12-24 hours.  The 5am weather balloon over Salem recorded a +19 degrees C at 850mb (near 5,000), and a northeast wind at 20 kts at 1,800′ elevation.  That north to northeast flow extends from just under 10,000′ to almost the surface.  So we have offshore flow in progress and a very warm air mass overhead.  That’ll give you 90+ just about any day between late May and early September.  The +19 over Salem is actually a bit warmer than modeled too.  So we may end up with +20 or +21 this afternoon.  The Crown Point wind sensor at Vista House had an east wind gust to 21 mph at 8am.  Not huge offshore flow, but the best of the summer!

Expect a quick warmup between now and noon as the warmer air surfaces and the downslope warming kicks in.  The heat doesn’t stick around long, although tonight will be a very warm one for late August.  Urban areas will remain at or above 60 degrees.

We have something else interesting on the way Monday and Tuesday.  A very wet system, an “atmospheric river” is going to sit over Vancouver Island later tomorrow through early Tuesday.   This contains tropical moisture and will dump a ton of rain up there.  Rain may get as close as a line from Hoquiam to Olympia.  Note the 72 hour rainfall total from the UW-WRF model.  This isn’t the usual North Pacific cold front either.  Precipitable Water (measure of total moisture in the column of air overhead) is going through the roof.  I see the NAM has it up to 1.60″ over Seattle with an 850mb temp still around +12 later Monday!   That system basically spends Monday-Wednesday dying over the Washington Coastal waters and Southern British Columbia.  So we get a ton of moisture on our doorstep and very little wind from any direction after today.  This is a setup for unusually humid weather and warm nights next week.  In fact that’s how I noticed it…MOS model temperatures show quite warm nights much of next week for the last week of August, so I went poking around to see why.  If the surface wind turns northwest or northerly after Monday, we’ll just be importing that humid air mass from the rain-soaked ground up north even if we are sunny.  I think this happened during the hot spell two, or three years ago?  I can’t remember the exact setup or which warm spell it was, but I remember Cliff Mass posting something about it.  I’m on vacation and don’t want to do that much work looking for it, maybe one of you could find it?

It’s really nice to have something to talk about weatherwise finally.  It’s been a very slow summer for the weather weenies…

Chief Meteorologist Mark Nelsen