September 01, 2020

A Dry End of Summer

Summers are typically dry in the Northwest, but by now the probability of precipitation typically rises significantly.

But this year we can look forward to a very dry end of summer--with no moisture for the next week or more.   

The precipitation anomaly (difference from normal) for the West Coast  over the past month shows an interesting story (see below).  Most of Washington has been slightly drier than normal, particularly the western slopes of the Cascades.    The southwest U.S. has been particularly dry, since the southwest "Monsoon", which typically brings thunderstorms in July and August to Arizona and New Mexico, has been much weaker than normal (a.k.a., the NONSOON).   And parts of California have been wetter than normal due to tropical moisture pushing northward (and causing all the lightning that ignited California).

The origin of our drier than normal weather has been an upper level pattern with persistent high pressure over the western U.S., but low pressure offshore (see the upper level map for the past 30 days, which shows differences from normal--yellow is higher pressure than normal, purple/blue is lower than normal). High pressure results in sinking air and dry conditions.

West Coast high pressure is going to build and remain in place, with the latest 7-day precipitation forecast shows NOTHING over Washington and Oregon (and California)--see accumulated precipitation  through Tuesday afternoon below.

Looking farther ahead in time using the highly skillful European Center ensemble, the prediction of the precipitation difference from normal over the next fifteen days (through 5 AM on Sept 16th) is for much drier than normal conditions (see below).  The reason?  Enhanced high pressure over the Northwest and to the east.

My water bill is already a source of discomfort and unhappiness.  This forecast will be costly.  A good thing is that the change of thunderstorms is also down, to the potential for new wildfires is greatly reduced.


My blog on the KNKX firing and cancel culture is found here.



  1. People talk about the 'golden hour', well this is our 'golden season' and I love it. It doesn't happen every year, but it's glorious to me. The views of the Olympics in this clear air are world class. No need to water those plants Cliff, a few drops at the base of the tomatoes and they'll be fine.

  2. looks like upper 80s possibly even 90s next week... september heat!

  3. I must say, the weather over the last 6 or so weeks has been one of the finest stretches I've experienced in my life. Truly perfect summer weather day after day.

  4. I have noticed, over the 6+decades of my existence here, that this trend to have a cooler first half of summer, and then finishing with a warmer experience, has been fairly consistent...It seems not unusual nowadays, to not have real summer temps until after the 4th of July...but as a kid, I would hit the beach at Green Lake in June frequently, with temps reaching at least into the mid 70s...and going back to school in September, meant walking in somewhat cooler temps, with leaves of trees beginning to fall...but now, September seems to hang on to August temps, at least for most of the month...Subjective maybe, but it seems true to me.

  5. My yard is looking pretty sad but, all these clear days and nights are letting me do lots of astrophotography.


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