The Almost Perfect Setup

March 27, 2006

Funny how just after I blogged about thunderstorms last Friday, tonight we have the perfect weather pattern for thunderstorms westside.  The only problem is that we probably aren’t warm enough.   Take a look at the map below.   It is the MM5 model from the University of Washington.  It shows the height contours at the 300 mb level (about 34,000′).  Notice the big upper-low off the N. California coast, and the flow around it coming not from the south, but slightly from the southeast.  That’s VERY good for thunderstorms west of the Cascades in the warm season.  As a wave rotates around the low, it encounters air that is "splitting" or diverging "apart" over Western Oregon.  Notice how some of the flow heads back towards the low and another part is headed up towards Washington.  That produces upward motion and can sometimes set off thunderstorms even in the middle of the night.  And with offshore flow at the surface due to the low offshore, we get warm weather down here at sea level too.  I have noticed that just about every single "thunderstorm night" we’ve had here in Portland in my career (since 1991), has been in this pattern.  Southeasterly flow with waves rotating up from the south or  southeast.  So hope for this pattern as we head towards summer!Snapshot_1  Oh, and I can’t figure out how to wrap the text around this image and it’s 11:20pm, so that’s the way it goes…Mark