Cool Spell Begins Saturday

May 30, 2012

We have two more warm days on tap, then it’s on to cool and occasionally showery weather for most of Rose Festival Week (what a way to fulfill a stereotype!).

What a nice day today with thin high clouds shielding the sun at times, but it was bright and warm.  We hit 73 here in Portland; at least up through 6pm.

Tomorrow the stationary front to our north slips a bit closer, and you can see a wave of moisture close enough to possibly bring sprinkles from Portland north.  Best chance will be in the morning and up against the Cascade and Coast Range.  You can see that on our RPM model:

A cold upper-level trough drops in over the West Coast Saturday.  This is the beginning of a cool spell as several troughs rotate into the Pacific Northwest during the following week.  It’s quite obvious on the 850mb ensemble charts.  First, the 12z GFS shows the quick drop Friday night, then below average until right after the Grand Floral Parade (Sat, the 9th):

The 12z ECMWF is similar, although it’s hinting at possible ridging around the end of next week.  The operational model (blue) is much warmer than the ensemble average (red).   It’s interesting that there ARE plenty of quite warm runs, but lots of chilly ones too holding the ensemble mean down below average:

Chief Meteorologist Mark Nelsen