Summer soaring meteorology - more is possible than you think

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I just got back from a trip out of town and saw Ron's double cascade crossing last Thursday (http://www.onlinecontest.org/olc-2.0/gliding/flightinfo.html?dsId=5384322). In the pilot comments section of the OLC Ron remarked in his usual low key style, "Over and back. Who would have thought, this late in the year?"

First of all, congratulations to Ron on a superb demonstration of his extraordinary pilot skills. There are few of us who have the abilities to pull something like this off. He continues to be an inspiration to those of us who are still trying to cut the apron strings.

Now, I don't want to take anything away from his awesome piloting, but what if I told you he had help, and that any of us could have benefitted from the conditions had we understood what was going on? Most of us view the KAWO XC season as over by mid-June and we either head to Eastern WA or just find other things to do. After all, isn't Western WA just a flat high pressure ridge for July and August with nothing but low level inversions that cap our lift?

Not every year, and certainly not this year. We have had an interesting summer if you were watching the upper atmosphere.

If you recall the article I wrote last Spring in eGlidepath on forecasting good conditions (http://evergreensoaring.info/content/spring-weather-holding-pattern), I pointed out that nearly all of our really good long distance flights in the Spring had one thing in common: rather large differences between the ground temperature and the 500mb temps. We don't fly that high, normally, but the two temperatures are easily found on forecast maps, so it makes a nice proxy for planning in the altitudes in which we do fly. The rule of thumb for a good day that I derived was a 40C difference between the two temps. If you think about it, that number makes sense since the 2C/1000 ft dry adiabatic lapse rate would yield 36C at 500 mb (around 18,000 ft). Because there are often small inversions along the environmental lapse rate line, the 40C seems to work better as a rule of thumb.

The max SL temps in the spring are slowly warming but still quite cool, around 15C, so to get the 40C difference we need from very cold upper air, about -25C at 500 mb. We're kind of expecting that in the Spring, and we look for frontal passage followed by a "warmish" Spring day.

But don't write off the summer. You can get that 40C difference another way. If the ground gets to 30C (86F), all you need is about -10C at 500 mb. This is where Ron got his help. Normally we have stable, warm, flat ridges accompanying our July-August weather, and any troughing you hear about is the useless thermal low at the surface off shore pulling hot Eastern WA air over the Cascades. But look below at the upper air map on the day Ron flew. He had -10C temps at 500 mb due to an unusual (for mid-summer) upper air trough. This has actually happened several times this summer, but sometimes the upper trough was so powerful it also ushered in crummy surface conditions as well (remember the Blue Angels' flat Sunday show?) You can see from the KUIL sounding that day that the atmosphere was very inviting, with the capping inversion occurring close to 10k ft.

The main point is, the summer may surprise you. Upper air charts are worth following. Sometimes it will be 90F at KAWO and all the air above will be flat and hot. Other times, however, especially near the end of August, the transition to Autumn is already slowly beginning with the remnants of Summer below and the first chills of Autumn at 500 mb.