The Dry Month Begins

July 8, 2009

junkI have to admit that I stole the idea for this graphic from Cliff Mass’s blog up in Seattle.   This is a graph of the rainfall probability for any one day throughout the entire year at PDX.  Notice the sharp dropoff after the 4th of July.  The month from July 10th to August 10th is the driest of the year here in the Portland area.  Of course each year is different, but the average numbers sure don’t lie do they?  I also see that September is a bit drier than June, but we quickly turn wetter after October 1st.   Basically we turn wetter faster in the fall than we dry out in the Spring and early Summer.

Coming up…looks like possibly some interesting weather for the end of the week.   The upper level low off of Vancouver Island is going to sag to the south and be sitting off the Oregon Coast Friday and Saturday.  It fills a bit as heights rise, but it’s definitely still there through Saturday.  Of course then that sets up the preferred south or southeasterly “thunderstorm” flow that we like to see.  Our RPM model and WRF-GFS imply something could drift off the Cascades Friday and/or Saturday afternoon.  But as we saw in June, we can have this pattern and still get no significant storms west of the Cascades.  It’s something to keep an eye on.

Mark Nelsen