Quick question I have about winds

flyer67flyer67
in General Discussion
True or False: When strong winds are perpendicular to a mountain range, you can expect mountain waves? I have been told false but my research states it is true.

Tom

Comments

  • Rikki0Rikki0
    True.

    From "Gleim Private Pilot Course" Section 7.6 "Expect mountain wave turbulence when the air is stable and winds of 40 kts. or greater blow across a mountain or ridge".

    The "King Private Pilot Course" video also illustrates the same thing. Hope this helps.

    Mike
  • flyguydonflyguydon
    It is true. If you go to test it... make sure of 1 or 2 things. 1 - have enough space AGL that you don't get swallowed up in it or 2 - have a lot of power that you can escape it if you do get entangled in it.

    Not good to have the escape out of the capability of whatever you are flying in...
  • PropFanPropFan
    There is a harrowing "Never Again" episode on AOPA's web site, which I can't seem to locate at the moment, about a pilot's encounter with clear air rotor turbulence in the Denver area. It was certainly caused by winds coming over the top of the Rockies. So, the answer is most definitely "True."

    Wikipedia: Lee Wave
  • PropFanPropFan
    There is a harrowing "Never Again" episode on AOPA's web site, which I can't locate at the moment, about a pilot's encounter with clear air rotor turbulence in the Denver area. It was certainly caused by winds coming over the Rockies. So, the answer is most definitely "True."

    Wikipedia: Lee Wave

    [Sorry about the duplicate post. Can't figure out how to delete.]
  • flyer67flyer67
    I did some additional research and this is what I found:

    When strong winds are nearly perpendicular to a mountain range, you can expect mountain waves, correct? Well not necessarily.

    Mountain waves require a very specific atmospheric structure before waves become apparent. Reasonably strong and nearly perpendicular winds along the ridge line are just one ingredient.

    Mountain waves can only exist when there's unstable air below the ridgeline capped by stable air above the ridge line. As the buoyant and unstable air is forced up the ridge into the stable layer on the windward side, it will be forced downward on the lee side of the mountain ridge.

    The air descends back into the unstable layer below the ridgeline and once again becomes buoyant and begins to rise back into the stable layer. This oscillation produces the mountain wave activity.

    If you see a lot of cumulus cloud activity along the mountain range, this implies the atmosphere is unstable above the ridgeline. This environment doesn't support mountain wave activity.
  • 78TARROW78TARROW
    I fly in the lee of the northern Shenandoah Mtns (peaks 3500-4500MSL) quite frequently. The ride in the lee varies quite a bit. Strong winds (30kt +) from perpendicular to 30deg or so from perpendicular can be counted on to produce moderate turbulence up to about 8,000ft. Mild mountain waves can be had with the atmospheric stablity criteria mentioned above. These can produce a lot of trimming in the cockpit but typically are not a climb performance challenge, even for a C172. They can extend 50nm or so east of the range and you can often see classic cloud patterns in the mountain wave region. Big lenticular clouds are rare. Others have said that the somewhat higher peaks in the southern Shenandoah can produce some sporty mountain waves and a lot more turbulence.
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