Summer is NOT over yet!

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 many of the models, including our ensemble prediction systems (ensembles are when one runs many models with slightly different initial states and physics) are indicating return to ridging, warmth, and dry conditions over our region starting next weekend.

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.

The joint U.S./Canadian North American Ensemble System shows a distinct warming trend starting after September 1 (see figure). The yellow boxes show you the range of the 50% of the ensembles surrounding the median value of the ensembles. The "whiskers" show you the extreme range. Little chance of rain and fewer clouds too!

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).