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Thread: Step Cloud on Snow Mountain

  1. #1
    Join Date
    Sep 2013
    Location
    Fremont, CA
    Posts
    220

    Step Cloud on Snow Mountain

    It's been a little while since I've flown. I was due for a BFR, so I scheduled one with Charlie last Friday, July 3. I also scheduled OJ for the afternoon in the hopes of going out to the mountains and dusting off the cobwebs. As we were doing my BFR, Charlie and I could see a line of rain approaching from the southeast. By the time we concluded the BFR (12:00 PDT), the front was almost at Williams and thunder could be heard. At the same time the Mendos were already popping nice CUs over Goat and Snow. We surmised that if I was to take off right then and go to the juicy looking CU, that at some point I would have to come back through the front, or be overtaken by it. It was an easy decision to wait until the front passed. But then I would also have to wait until the front cleared the mountains and it would also most likely kill all the activity on the Mendos. The other thought was that maybe it might be a post-frontal valley day right after the front passed. Oh well, I was there and I was going to do some flying one way or the other before I left!

    I was pleasantly surprised to see Andy (EH) there when I came out of Charlie's office as I hadn't seen his name on the schedule the night before. Jim was also there and scheduled to fly 88. At about 2:30 we were all ready to go. I was elected to be the canary in the coal mine and towed first. I asked Marty to tow me to the backside of the front, which was now on the Mendos near Goat, in the hopes of finding some lift under the small ragged CU that were in it's wake. It was probably the smoothest tow I've ever experienced going out to the mountains. Not a single bump. Noelle was towing 88 right behind us. I got off near Goat South Pass, and after a brief search was retreating down the Goat spine to Walker Ridge thinking that I wasn't going to find anything there either. But the front must have missed Walker, or not dropped much rain there, because it was working.

    88 soon joined me on Walker Ridge and EH elected to tow straight there based on our reports. Now all we had to do was hang on at Walker long enough for the sun to get the Mendos kicking again. I tried to go back up the Goat spine after a while, but didn't find anything before retreating back to Walker. Andy crossed Indian Valley Reservoir and was climbing up the ridge which intersects the Goat spine. I soon followed him. After several retreats on my way up, I finally made it to Goat. CUs were starting to form again and a nice step cloud had formed on top of Snow. Here's the view I had near Letts Lake looking north to Snow.

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    I was just beginning to fly directly to it when I noticed some little wisps forming to the west of my location. They looked like little stepping stones leading right to the step cloud!

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    They were marking the convergence line which was responsible for the step cloud. You sometimes see these out in the blue between clouds on the Mendos. And while they aren't often strong enough or big enough to circle under, they show you the best line to fly. I altered my flight path to get under the little wisps. You can see where I altered my course line on my SeeYou trace at the red arrow.

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    I probably would have been fine just flying directly to the cloud since it wasn't too far away. But I remember hearing or reading somewhere (one of Kempton's talks maybe) that altering your course line up to 10 degrees is worthwhile if you can get into a better energy line. This is especially true if you have a large distance to cover!

    Pat

  2. #2
    Join Date
    Sep 2013
    Location
    Fremont, CA
    Posts
    220

    Re: Step Cloud on Snow Mountain

    Or maybe it was up to 30 degrees? What say the experienced cross-country pilots? How far are you willing to divert off course to get into a better energy line? Does it depend on the distance you need to travel? Any rules of thumb?

  3. #3
    Join Date
    Mar 2011
    Location
    Central Coast, CA fly out of Avenal, CA
    Posts
    39

    Re: Step Cloud on Snow Mountain

    Crikey, the damn forum software ate my response when I tried to attach an image by drag-n-drop. Lesson learned.

    Generally speaking, deviate larger degrees early. A 90 degree deviation for a mile or two might make sense at the beginning of a long run. There are plenty of books with details on deviations, mostly having to do with contests. Often those are examples that are referring to more classic McReady theory. In our convergence flying, we see much more concentrated energy lines than simply a good cloud 45 degrees off our course line. That means we see larger deviations pay off many times.

    Attached is a diagram of a typical deviation we fly out of Avenal when returning home. Heading out, we usually can't get high enough to even have the straight line as an option. The long way is usually about 7 miles farther, but it is almost always faster. Only the luck of a booming thermal centered in one turn will typically allow the straight line to be faster. I still try it sometimes, but it's almost always faster to go the long way at higher speed staying higher.

    I suggest just using some simple examples to play with numbers and try out what-if scenarios.

    60kts for speed to keep the math easy. You can even use Skyvector.com to plot out a deviation and then adjust the speed so it will do the math for you regarding time to cover the distance. You just have to make some educated guesses about the kinds of altitude differences you'll end up with.

    A sample might be a 90 degree deviation of 1nm, followed by a 5nm glide. Versus just a straight 5 nm glide. Assume some sinky air on the straight glide resulting in 30:1 performance. You lose 1000ft going straight. Assume lifting air along the deviation. You lose 200ft to get to the line, then zero along the line. You arrive at the next good cloud 800ft higher and 1 minute later than the straight glide.

    How often do you stumble straight into 8-10kt cores? Not often enough likely. So in that simplified scenario you can see that the deviation will generally pay off.

    The more you mentally practice these scenarios, the more easily you can recognize a good pattern when flying. Lone cu 2 miles right of course line when you're 5 miles away from the next cu on course, probably not a good use of time. A line of wispies 1/2 a mile off your wing, almost surely worth the deviation.

    In the convergence, the markers are almost always the line to fly. I weave a lot in order to not circle and that usually allows me to post some relatively high speeds for our lower altitudes and unballasted flying.

    Good questions though.

    Morgan

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  4. #4
    Join Date
    Jan 2011
    Location
    Menlo Park, CA
    Posts
    994

    Re: Step Cloud on Snow Mountain

    Pat,
    Great shot! As Gavin Wills stated, the Mendos act like the NZ Alps (or perhaps the NZ Alps act like the Mendos...)

    Anyway, I submit my best step cloud pic, from last year, April 27 2014, Rumsey S bound:
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    Keep those pics coming!

    Re: acceptable deviation from track, I'll post to a separate thread my find!
    Kemp
    ASH-25 (FNX)

  5. #5
    Join Date
    Sep 2013
    Location
    Fremont, CA
    Posts
    220

    Re: Step Cloud on Snow Mountain

    Morgan,

    Thanks for your input. I agree with Kempton's assessment on an earlier thread that we should have you come up and be one of our speakers in next winter's seminar series!

    Kempton,

    Thanks for starting the other thread with the link to the FAA Glider Pilot's Handbook and including your best step cloud pic! Here's my best step cloud pic, taken exactly three years ago today on a flight out of Minden.

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    Devin Bargainnier and I were returning from Mt. Whitney and the pic was taken east of Mt. Patterson looking west. We didn't divert to it as we were already on final glide back to Minden. Here's another shot taken 6 minutes later as we passed it.

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    More pics from that flight and my account of it can be seen here:
    http://mindensoaring.blogspot.com/2012/07/to-mount-whitney-and-back-with-six-pit.html

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