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Speak of the Devil

Robert Moore diablochair@wingsofrogallo.org

Summer Flying at Diablo

After nine months of soaring Diablo at its finest, the Diablo Team is usually ready to spend some time at our favorite sites not available during other times of the year. Team members seem to scatter in all directions to take advantage of big air during high summer. When returning from these trips I can always see Diablo from a great distance. Typically, I say to myself, "There's my mountain!"
While Diablo is not our focus during mid-summer, we still find ourselves drawn to the mountain when we are staying local for the weekend.
The devil-mountain can be a cantankerous old cuss in the summer. Hot summer afternoons can bring sweet glassoff-type conditions, rowdy bullet thermals that seem to be going nowhere fast, or trashy inversion-layer turbulence. Cross-country flights have been made during mid-summer, but it's usually quite a struggle.
My comments will be divided into two sections: What to Watch For, and What to Watch Out For. I will start with the warning section, since the Devil loves to catch the unwary.
For better or worse, Diablo does its own thing. Don't expect conditions at Mission or Ed Levin to be truly reflective of what will happen at Diablo. Forecasted wind directions for the Bay Area often don't seem to apply to Diablo. There are several factors that play into this fact, but the most important thing to remember is to stay aware of what is happening to conditions as best you can.
A classic example of how changing conditions can ruin your day is the potential shift of wind direction from northwest to southwest. While driving up the mountain, you notice that there is very little wind. Stopping by the Juniper launch, there seems to be nothing much happening, but when you get to the NW launch it's coming in light and straight. During set-up you see a few cycles that are pretty left-cross, but there are still straight cycles, too.

Beware - if the majority of the cycles are left-cross you should strongly consider not launching. The NW launch is pretty well shadowed from SW airflow until it gets around 10 MPH, and this speed will increase as altitude decreases. If you launch into one of the straight cycles, you will have a very fast, turbulent, sinky and generally uncomfortable flight all the way to the LZ - assuming you reach the LZ. Quite a few pilots have been forced into bailout LZ's, kissed the ground in thanks for a safe landing, then hiked their gliders out a considerable distance to a retrievable road.
Another classic summer condition is that of differing wind directions at different altitudes. The mountain is high enough above the LZ's that this is not uncommon. A SW launch at Juniper can end with a NW wind at some of the LZ's. A NW launch can have SW flow at Mitchell Canyon LZ. Pilots must watch for signs of changing wind direction at launch, in the air, and on landing. Exercise those H4 skills to stay out of trouble.
Watch out for the inversion cap. While the other Bay Area sites fit neatly within the typical summer inversion layer. Diablo often protrudes through it. Sometimes this can lead to flying through a particularly trashy zone just beneath the cap. Pilots have occasionally experienced big-air style turbulence in that zone and been glad to sink further below it. This turbulence can be particularly dangerous if encountered while flying near terrain or other pilots.
The bullet thermals a Diablo are surprisingly nasty, given that it's not a big-mountain site. These little devils want to knock you around, and if you try to core them they seem to disappear. Expect these conditions on warm-to-hot summer days with a SW flow. Okay, enough with the dire warnings, let's look at the good stuff. As stated earlier, Diablo does its own thing, and sometimes it can be quite good. So many times during the summer I have been told the soundings are dismal. There's no point in even hoping for lift, the inversion is unbeatable. The

Devil-mountain, however, has proven the soundings wrong on many occasions.
My favorite condition on those heavily inverted summer days is when the winds stay light NW all afternoon. Launching after 3 PM at the NW launch on these days often finds generous lift all around the windward side of the mountain, and one can fly about with ease. The inversion cap seems to have been pushed higher, and is less pronounced. One can explore the various peaks, canyons, ridges and other features that populate the north side of the mountain. XC is possible, depending on the altitudes reached.
Good flying conditions can also be found on SW flow days. Because Juniper launch is so nicely contoured, stronger wind conditions are easy to launch and soar. The SW face of the mountain is a continuous ridge that captures thermals quite well.
Summer flying at Diablo is never boring. Whether a pilot is hanging tough with bullet thermals, or site-seeing while boating around in smooth lift, the mountain always likes attention. Those who wish to get the best Diablo has to offer tend to visit regularly. I hope to see you there.