How to avoid rotors and other dangerous turbulence around mountains?

Question

I would like to try flying around some mountains but have never done so before. I am aware of some things to look out for:

• Lenticular clouds (a sign of mountain wave)
• Flying on the leeward side of mountains (where the wind is coming back down)
• The minimum safe altitude

Are there any other factors to be aware of? What is the best way to ensure you don't hit rotors that throw the aircraft out of control?

FYI an answer like "stay much higher than the mountains" won't help as I want to practice ridge soaring and using thermals for lift.

Answer 1

Flying in mountainous terrain in the UK, with the highest peak at about 2000 ft isn't quite like the Alps or the Rockies, but it's still enough to get you into trouble if you're not careful.

The biggest risk is rotor below the lee side of ridge peaks, so never cross over to the downwind side of a ridge without ample altitude above unless the winds are very light. If a lenticular cloud has formed on the lee side of a peak, the rotor is just below it. Hitting that sort of rotor on a windy day will be like a wake turbulence encounter with an airliner.

Other risks:

• Below the rotor, downdrafts or downsloping air on the lee side of ridges.
• Flying up valleys that are sloping uphill and you can't tell because you don't have a direct horizon reference. Adding to that, blundering into an uphill valley and not leaving room to turn around once you realize you've blundered into an uphill valley.
• Winds are everything. Up a valley, down a valley, across a valley. What the wind is doing is probably 80% of risk management. You have to learn to mentally picture what is happening in the different parts of a valley for a particular wind direction, and you have to be able to discern the wind direction.

Read some books on mountain flying.

Also suggest you follow some channels of paraglider pilots in the UK that do cross country in the Scottish Highlands and the Lake District. The paraglider guys are, for obvious reasons (gossamer delicate wings), the most sensitive to the risks by winds and you can learn quite a lot from them. Plus the channels of glider pilots that do ridge soaring.

Get educated, then maybe go out with somebody with experience to show you the ins and outs.

Answer 2

Are you testing the water, seeking deniability? If you want to learn to fly in thermals, try west Texas, or even southern Arizona. Regarding wave soaring and the dangers related to clear-air conditions in the lee of the ridge, here is something to think about as reported in an updated Plane and Pilot article dated February 16, 2016 -

The NTSB says the probable cause of the 2007 crash of adventurer Steve Fossett was an inadvertent encounter with downdrafts above mountainous terrain that exceeded the climb capability of the Bellanca Super Decathlon he was flying. Downdrafts, high-density altitude and mountainous terrain were all contributing factors. None of those factors should be taken for granted by pilots who fly, or have a desire to fly, in mountainous areas. In simple terms, while wind flows smoothly up the windward side of a mountain, and the updrafts can be used to help an aircraft make it over the crest of the terrain, downdrafts on the leeward side can become terrifyingly strong and turbulent. Areas of turbulence and downdrafts can be surrounded by deceptively smooth air. Just because there are no lenticular clouds, rotor clouds or dust storms doesn’t necessarily mean that conditions are benign. Before conducting a flight in or near mountainous terrain, an experienced pilot should carefully evaluate the weather, especially winds aloft, approaching frontal activity and stability information such as the [lift] index. A smart, inexperienced pilot will confer with someone who knows how to evaluate conditions, and also get a checkout with an instructor qualified to teach mountain flying before venturing into unknown territory.

The emphasis, above, is mine. In concluding an answer to the question on se-aviation, "What prevents a small plane like a Cessna or Piper from flying as high as a jet?" I noted the following incident regarding rotors -

In 1952, Larry Edgar and Harold Klieforth set an altitude record in a two-place Pratt-Read G-1 glider, soaring to 44,255 ft (13.489 km) in a Sierra wave. However, on April 25, 1955, Larry Edgar's Pratt-Read glider was destroyed in the lee of the Sierra by a rotor-cloud at 17,000 ft (5.2 km) as he was investigating the rotor's turbulent structure at the base of a wave. The acceleration he experienced, in excess of -20g, ripped off his helmet, boots, gloves, and oxygen mask. As he drifted downward he could see parts of his glider being carried upward and worried if he pulled his parachute rip-cord, he might be carried upward as well. Fortunately, he was able to make a parachute landing and survived without breaking any bones. The extreme negative acceleration partially damaged his vision. Edgar was the only one in his sailplane when this happened.

One may think that wave soaring is thrilling in the quiet, clear air at 33,000 ft above the Sierras, or central Rockies, or even the Tetons; air so quiet the only sound one can hear is the tapping of the yaw string on the canopy. But my concluding comment to that answer was the following -

Aviation, although not inherently dangerous, is, to an even greater extent than the sea, terribly unforgiving of any carelessness, incapacity, or neglect.