The return of some clouds and showers to the Northwest has induced some wringing of hands: is our wonderfully warm and dry summer over? The answer is decidedly no.
The forecast models suggest that after a cooler, cloudier period this week, warmth and sun will return.
The key feature of the next 5-6 days will be a trough of low pressure that will be parked off our coast, as illustrated by this 500 hPa upper-level chart for Wednesday morning. Far enough off the coast to provide some clouds and perhaps a few passing showers...worse on the coast and far warmer in eastern Washington. You can get thunderstorms, particularly east of the Cascade crest, with this pattern.
But before I show these forecasts, a bit about September climatology. September has become a fairly good month here in the NW. Take a look at the average highs at Seattle Tacoma. If you look closely you will see that there is only a few degree drop between mid-August and mid-September. The is even more evident in the extreme temperatures..virtually no decline until late September.
Now for the encouraging stuff. Take a look at the OFFICIAL 8-14 day forecasts by the Climatic Prediction Center (CPC) for precipitation and temperature. Below normal chances of rain and above-normal temperatures.
Too complicated? Here is the departure of the mean 850 hPa temperature from normal forthe NWS ensemble forecasts for September 4th at 5 PM (this level is at about 5000 ft). Warmer than norma; (yellow and orange colors).
OK..I know this is out pretty far. But certainly reason to be hopeful that this pleasant summer will continue into early September.