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Warning do not enter - visible mountain wave clouds


Ed Cesnalis

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Great picture.  Is the result of entering those clouds similar to going thru the spin cycle in a huge washing machine?

 

Dick,

 

The big smooth looking lenticular could be surfed in a CT but I might be impossible to stay out of the flight levels once you get to the lift.  You would surf on it more than fly in it.

 

Then there's the batwing looking rotor clouds indicating some of the rotors.  These guys tend to cause rapid descents only after they put you in an unusual attitude.

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Tell those of us who haven't flown in the mountains yet, are you noting the left to right dark bluish waves clouds?   How does the danger manifest itself?

 

The wave clouds are more common and most often indicate winds aloft like in the flight levels. Gliders surf these waves all the time.  The little rotor clouds are indicating what is happening down lower in the canyons and they indicate conditions that concern me more than the lennies do.

 

Big waves or little its the ones you can't see that will get you, when the waves/rotors form clouds you can see whats going on.

 

The dangers are: excessive lift that you cannot overcome; sink that you cannot overcome often beginning with an upset.  You don't want to be in a place where you are going to loose more altitude than you can afford.  

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In Ed's photo the high band of dark, smooth, undulating clouds are lenticular clouds. They mark peaks in the flow stream at one level in the standing wave system. The wave likely extends higher, but the higher levels happen to be dryer in this case, and thus no clouds form.

The bright, fracto-cumulus clouds just below the lenticulars are roll clouds. They mark rotors in the wave system. Like the lennies, the upwind side of the roll cloud is going up and the downwind side is going down. The rotor typically contains sharper gradients between lift and sink and this turbulence may extend to the ground. And again, like lennies, there may be no roll cloud at all if the air mass is dry at the rotor level.

The fact that the lennies are dark and the roll clouds are bright is only a reflection of the low sun angle when this photograph was taken. Lennies are often bright as well.  

Although not pictured here, a third common wave cloud is a cap cloud. A cap cloud generally looks smooth like a lennie but is located directly on the ridge, extending below it on the downwind side and obscuring the peaks. This is in contrast to the lenticular and roll clouds which are located in standing waves downwind of the ridge.

The first drawing on this web page gives a nice simplified diagram of typical wave system. The second diagram showing the lennie over the peak is not typical at all, though it would be a nice drawing of a cap cloud is it was down on the peak.

The guidance given in the "solutions" section of the above web site was intended for much larger aircraft. Aircraft with light wing loading, such as our CT's, should avoid wave conditions all together. However, should you happen into wave, slowing down is good advice. Leaving the flaps up will also help to attenuate maximum loads. Tightening seat belts and securing loose items in the cockpit is also appropriate. And finally, turning downwind is often a quick way out of wave sink. Your turning away from the high terrain that is generating the wave and you get a boost in ground speed to get you out faster.

Mike Koerner

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Very well said Mike thanks.

 

The big take-away here is visualization.  These same winds occur without the tell-tale clouds but you still have clues.  I study the patterns when they are visible so I can understand what happens when they are there but not visible.

 

Toe-in-the-water testing, is what I do.  Say the winds are typically SW @ 15kts @ 12,500'.  Probably lower winds down low and higher up high.  These conditions are borderline  for photography, might be great, might be impossible, so as I approach the rotor zone I am ready to turn back depending on how it feels.  Often some areas will be smooth while other areas have lots of action.

 

I have been crossing the Sierra for 30 years and have found crossing can often be done at low altitudes when all the action is above you. West to east works much better thane east to west and even if your entire crossing is smooth you generally have to descend through a rotor after you cross.

 

Its good to know that as I approach terrain downwind I encounter lift and after crossing turbulence and sink.  As I approach terrain upwind I make sure I have extra altitude and room to turn around.  Sink in front of the terrain can rob you of the altitude you need to clear and do it at the last instant.

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The wave / rotor / micro-burst may be the blue sky variety so I photograph in the peaks at 90kts IAS not 65kts.  The extra speed is a big detriment but it means I have energy in reserve and if I encounter sink that is going to put me in the terrain I can always zoom up 600' and swap ends doing a 180* turn using no room.

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This is all so intimidating!   I'm not sure how I'll ever fulfill my dream of flying coast to coast and back in a CT, let alone a Cub or a Champ.   I guess that's a little dumb, since thousands and thousands of pilots have done it.   I just haven't yet figured out how they figured it out.

   Thanks for the patient tutorial.

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CT, once you are in or near these things, and get caught up in the up/downdrafts, can you turn away from them to escape?  Or at that point is it just too late?

 

It depends on how you fly.  It depends on how you encounter the shear.

 

How I fly:

  • 90kts+ IAS - this means energy in reserve.  If I can't out-climb the terrain in front of me and there is no room to turn I can wing-over and reverse course.
  • Altitude margin.  Its both fun and dramatic for photography to clear terrain without margin.  If you are flying upwind there could be room for a down-draft at the last moment. I use more margin upwind then down.  Downwind the approach tends to be buoyant. 
  • Angles - Crossing ridges at angles either increases or decreases your margin for turning away.  I set myself up for an upwind escape with the small turning radius.  Think Cory Lidle and Hudson river 10 years ago.

Encountering the shear:  Important to have belts tight and loose items secure.

  • Positive wind shear:  In the wave this can provide climb you can't counter.  Busting 18K, overspeeding, and O2 or concderns.  In the rotor it can mean an upset.
  • Negative wind shear: Don't stall, turn away - or towards lower terrain  - or turn to escape the downdraft.
  • Rolling over:  You likely have to recover then turn towards safety.  Good instincts from training help here.  

 

Most of this is easily avoidable.  Don't fly in the rotor zones with winds above 20kts.  The Victor Airways  are located in the most crossings (sometimes, look and consider)  Reference your wind indicator often.

 

The hard to avoid encounter happens on the west to east crossing.  I know where to find a smooth crossing (V230) but once across I have to descend through the lee side rotor.  This can be eventful but usually short lived.  If the rotor goes all the way to the ground I either divert to Bishop of more likely go fly a 10 minute circuit to the north and come back and try again.  Conditions like these undulate, they are down to the ground for a period and then they are aloft or away from the airport for a period.  Luck timing gets me on the ground.

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This is all so intimidating! I'm not sure how I'll ever fulfill my dream of flying coast to coast and back in a CT, let alone a Cub or a Champ. I guess that's a little dumb, since thousands and thousands of pilots have done it. I just haven't yet figured out how they figured it out.

Thanks for the patient tutorial.

I have hopes of flying to the Seattle area eventually and have flown with another pilot from eastern WA back to ND.

There are a couple of books out there that are known for good information. Sparky Imeson and Fletcher Anderson are the authors.

When I do this I plan to stop and get some instruction on mountain transition. (A different animal than true mountain flying from what I understand.)

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Related, but different.  Coming home from the Fly-in, flying wide on the downwind side of a 13,000' mountain, we caught about 5 minutes of serious 500-750 fpm UP.  Went from 6500 to 9500+ like an out-of-control elevator.  Winds were 48-53+ @ 1oclock.   'Never did get any sink.

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CT and I live in Sierra Nevada mountain country.  Mountain wave winds, rotors and turbulent updrafts are dangerous if not trained to recognize and deal with them.  They can occur anytime of the year.

 

The first telltale that mountain wave or a rotor is present is a lenticular cloud over the ridge and/or lenticular clouds dotted across a valley in an analog sequence evenly spaced at the same altitude.  These are the tops of the updrafts.

 

If you are flying into the wind and need to clear the ridge then fly at least half the height of the mountain in front of you and at a 45degree angle.  If that exceeds your ceiling or safe altitude then don't go there.

 

Stay away from under ragged or irregular lenticulars as they will be turbulent and have more extreme wind effect and you may not have the power to escape.

 

Climb in lift and dive in sink.  This will give you better control than trying to fly level in either updraft or downdraft.

 

When flying were mountain wave is present fly out on an updraft.

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  • 3 weeks later...

I got my private pilot's license while stationed at NAS China Lake.  Remember trying to get up through Walker Pass over to Kern Valley in a Cessna 152 with strong winds out of the west.  Don't remember there being any lenticular clouds but know I did think about the possibility I could meet up with a lot of downdraft. As I approached the east side on the Sierras, I remember being in a full power climb going 500 fpm down.  I turned downslope to escape.

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