Tuesday, August 24, 2010

Adios, Summer

Enjoy today and tomorrow, summer lovers. This is most likely the last extended taste of summer that we will see. Most of Oregon will be looking at temperatures above 80 degrees today, and here in the valley it will be closer to 90 degrees. Wednesday looks to be similar with plenty of sunshine. But then we hit a wall. Is it the Autumn wall? It very well could be. Our average temperatures are now on the decline. Portland topped its high average temp at 81 degrees earlier this month. By the end of August, we will only average 78 degrees. And looking at the 7-day forecast, we are aiming below that to close out August.

The extended outlook does not look promising for a return Summer. Here is the 500mb chart for this coming Sunday. This map looks halfway up the atmosphere and gives us a good indication of where storm systems are going, they usually follow the lines. The X's mark vorticity maxes that indicate areas of unstable atmosphere. Notice that big dip in the lines that point in our direction. This means that cooler weather from Canada will sag our direction and usher in clouds and below average temperatures.

Now, I am not calling for that grey, soggy winter weather. I am just pointing out that we have begun the transition out of summer. You will notice cooler mornings and crisper air. It really reminds me of football season. There could be nice, sunny days ahead. But those days won't be as warm. The sun angle is diminishing and thus not as powerful.
I have heard a lot of people complain about how our summer has "sucked". I only assume they think this because we had several cloudy mornings before the sun came out. They are right. Since 2000, Portland averages 13 days of cloudy starts from July 1st through August 5th. But in 2010, we have seen 20 out of 36 days begin cloudy (info courtesy of Rod Hill). We could add more to that total since the 5th of August, but that would already be adding insult to injury. But just because we start 55% of summer days cloudy does not mean that our summer has been a wash. Portland has had only 0.01" of measurable precipitation this month. That is 0.60" below average for August. We finished 0.13" below normal for July. So we have been relatively dry this summer, if you discount the fact that it took us something like six days to set the June rain record, we finished 2.68 ABOVE average in June. Personally, I have enjoyed the summer weather. Where do you fall?

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