Next 10 Days: The Big Picture

November 4, 2010

Lots of speculation on the blog and elsewhere about the next 1-2 weeks.  The really long range period has shown flips of either warm ridging over us or a cold plunge of air.  Each model run has been different.  Here’s the big picture:   It’s pretty tough to read, definitely click on the image to see a better view.  It’s the 10 day upper-air forecast (500mb) from the GFS and ECMWF on top, then just below each is the ensemble run average from each.  Off to the right on it’s own is the Canadian model ensemble.  The basic message is the same on all of them.  A ridge of high pressure (very strong on operational runs) is centered somewhere between 130-140W longitude.  Here are my thoughts on that:

1.  A strong ridge in this location should give us drier than normal weather in November, weak waves will ride over the ridge and dive down into the middle of the country or the Rockies.

2.  We can get shots of cool air, but any real cold weather would be far to the east.

3.  If the ridge develops slightly farther west (around 150W), that allows cold Canadian air to plunge south.  Several model runs have occasionally done that the last 3-4 days.  But if the ridge comes slightly closer to us, then it cuts the moisture off even more for mainly dry weather.  This accounts for the drastic run to run changes.  A slight change in the ridge location has dramatically different results for Pacific Northwest weather.

4.  This takes us into mid-November; so we can eliminate a surprise early November freeze like 1955 as some of us were hoping for.  In 1985 (the OTHER cold November), the cold air action didn’t get going until the 2nd half of the month…there’s no reason that can’t still happen.  Cross your fingers for that.

Short term weather?  Cooler and cloudier tomorrow and Saturday, but the only significant rain coming up holds off until Saturday.  Much cooler with some mountain snow early next week, but it doesn’t look real heavy for now.

Chief Meteorologist Mark Nelsen