Back to the Sunshine

September 25, 2008

Snapshot  I'm trying to stay ahead of the ball tonight (not really a reference to the OSU game, although I suppose it's timely).  The weather forecast is somewhat simple.  Last night's cold front has moved well off to the east, leaving us in weakening onshore flow.  When I showed up at work around 1pm, you could clearly see the surface low off of Vancouver Island.  That has now dissipated and moved inland.  Surface high pressure builds inland tonight, giving us weak offshore flow tomorrow.  That plus warmer air in the atmosphere overhead should give us about 10 degrees warming.

An upper-level trough passing by to the north Saturday keeps us from warming more than a degree or two.

All models are now in agreement with a strong upper-level ridge rapidly building directly overhead on Sunday.  This is partly due to deepening storms in the Eastern Pacific.  500mb heights go up to 586-588dm by Sunday evening.  That's a very warm atmosphere, especially for the last few days of September.  And it'll be centered directly overhead on Sunday and early Monday.  This time of the year it'll be easy to get easterly wind with this setup.  In fact Sunday and/or Monday we may see 80 degree temps at the Coast assuming the easterly flow makes it that far.  12z models had shown the thermal trough making it out to the beaches, and now I see the 00z NAM has easterly flow stronger near the surface than up at 850mb…that looks more like Fall than Summer.  It goes without saying that we're going to have one (last?) "heat wave" to wrap up this month.  That's why I put Monday's high up to 90 degrees.  850mb temps of +22 and easterly wind to PDX should do it.

The other piece of agreement in the models is in the long range.  They keep pushing the arrival of some wetter westerly flow farther into the future.  12z and 18z models all showed rain holding off until after midweek.  The combination of southerly upper level flow and/or easterly surface flow is going to keep us warm through the first day or so of October…Mark Nelsen