Tuesday, September 26, 2017

The Last Warm Days of the Year

Today in the Northwest was as close to perfection as one could get:  a high of 74F in Seattle, with much of western Washington in the 70s (see map of today's max temps).  Sun, no smoke.


We have two lovely and even warmer days ahead, with Seattle zooming up to around 80F on Wednesday and Thursday.  The origin of this boon?  A temporary ridge of high pressure over the West Coast (see upper level map for tonight at 11 PM).

But everything changes on Friday as the ridge is replaced by an approaching trough...and no ridge is coming back for two weeks (as far as we have forecast skill).  And then it becomes too late for sustained real warmth (75F and more), as the days shorten and the sun weakens.   Here is the Weather Channel (weather.com) forecasts for the next two weeks.  Highs only reaching into the upper 50s by the end.


What about the North American ensemble combining U.S. and Canadian extended range forecasts (see below) through October 10th?  The top panel is temperature (C), followed by precipitation, wind speed, and cloud cover.  The range  of the ensembles is shown by the "whiskers"  and 50% of the forecasts are within the yellow bars.

The ensemble are united in predicting the warming, followed by a cool down for several days.  Then a modest warming, but not back into the 70s.   Light rain on and off.

There is still plenty of water in Seattle's reservoirs (see figure), and the Yakima

River System is above normal (also see below) due to the bountiful spring rains.


But water levels are dropping rapidly (which is normal) and it is time for the fall refill.  

1 comment:

John K. said...

Nothing more enjoyable than a cool day with bright sunshine. Even more so with the great colors and contrast given the low-angle sunlight. Best time of the year by far.