Every region of the country has actually its distinct obstacles for pilots. I tend to think of the Northeast, wright here Premier Flight Center is located, as the “Airroom Capitol of the World”. Yup, if it’s the complexities of airarea you want, you’ve gained it here! Pilots that endeavor out in the Amerideserve to West have a whole new challenge facing them – mountains, and also every one of the complexities of mountain weather! Below are some awesome shots of one of those mountain weather spectacles, standing lenticular clouds.

You are watching: Crests of standing mountain waves may be marked by stationary, lens-shaped clouds known as


As one alert reader observed, “fabulous photos, and from what I have actually read, finest taken from the ground.”He"s ideal, and let’s testimonial why. Standing lenticular clouds are connected via a phenomenon well-known as mountain wave turbulence.

But first: A quick review of stability

Our setting, the envelope of air surrounding the planet, is always in motion. We tfinish to think of the movement of our setting as horizontal throughout the ground, namely wind. However before, air have the right to move vertically too. An air mass, a big body of air that has almost unicreate qualities of temperature and moisture, is classified as either steady or unstable.

Stable air resists vertical activity. This is not to say that it cannot move vertically; fairly, if it is disturbed by some outside pressure, and disinserted vertically, it will not proceed to move upward of its very own accord. Aacquire, secure air resists vertical activity. Conversely, unsteady air, as soon as disturbed vertically, will certainly continue upward for some time, and probably also acceleprice vertically.

Mechanical turbulence

As air flows alengthy the surchallenge of the Planet, it encounters obstructions. These are fabricated objects, such as structures and bridges, and herbal attributes, prefer hills, valleys, and mountains. All of them disrupt the circulation of air right into eddies. The toughness of the eddies relies on the dimension of the object and also the rate of the wind. It results in turbulence we classify as ‘mechanical’ because it is developed via the “mechanical disruption of the ambient wind flow”. Infact:

“The level of mechanical turbulence counts on wind rate and also roughness of the obstructions. The greater the rate and/or the rougher the surchallenge, the higher is the disturbance. The wind carries the rough eddies downstream – exactly how much relies on the wind speed and the stability of the air. Unsecure air permits larger eddies to develop than those that develop in stable air; but the instability breaks up the eddies conveniently, while in stable air, they dissipate slowly.” web page 82 Aviation Weather, AC 00-06A, 1975
“As unstable air crosses the obstacle, it spills dvery own the leeward slope often as a violent downdraft. Sometimes the downward speed exceeds the maximum climb price for your aircraft and also may drive the craft right into the mountainside. In the procedure of crossing the hills, mixing reduces the instcapability to some extent. As such, hazardous disturbance in unsteady air mainly does not extfinish a good distance downwind from the obstacle.” page 83 Aviation Weather, AC 00-06A, 1975

Think of it like this: If you throw a rock into the ocean wright here it’s crashing versus the shore, you may finish up through a bigger splash if the water from the splash combines through the wave at the ideal time, just as the wave breaks. You won’t gain any type of ripples though because the wave’s action dissipates them. However, throw a rock into a relaxed lake and also the ripples will certainly propagate for a long distance!

Unstable air is analogous to the choppy ocean along the shore, and also stable air is similar to the lake.When unstable air is obstructed by a hill, it aggravates the disturbance it produces on the windward side and also along the crest. The rough air then violently descends on the leeward side. Pilots should be especially conscious of this situation, as the picture reflects, bereason the downward speed of the air have the right to be incredibly great!

Mountain waves


The number over mirrors a cross section of the standing wave pattern that creates downwind of a hill as a result of secure aircirculation across the crest.

“When stable air crosses a hill barrier…air flowing up the windward side is relatively smooth. Wind flow throughout the barrier is laminar – that is, it tends to circulation in layers. The barrier might erected waves in these layers a lot as waves build on a disturbed water surface. The waves remain nearly stationary while the wind blows promptly with them. The wave pattern is a ‘standing’ or ‘mountain’ wave, so named because it stays fundamentally stationary and is associated with the hill. The wave pattern might extend 100 miles or more downwind from the barrier.” Pperiods 83-84 Aviation Weather, AC 00-06A, 1975

Keep in mind just how the wave pattern from a mountain wave exhas a tendency not only horizontally for many type of miles, yet also vertically. In truth, a mountain wave action and disturbance deserve to influence aircraft at altitudes right into the lower stratosphere, which generally starts around 30,000 to 35,000 feet above sea level!

Clouds connected with mountain waves


Photograph taken southern of Walsenburg, Colorado on May 20, 2003Photograph by: Mark J. Madigan

If the air includes adequate moisture wright here a mountain wave forms, tright here may be clouds which provide an indication of the hill wave problems. You might view a cap cloud straight over the hill, as pictured over. Cap clouds indicate that tbelow is a strong wind circulation dvery own the slope on the lee side of the hill. You can imagine horizontal streams of air flowing over the mountain, as were diagramed over. Where the moist air cooled sufficiently as it rose to cross over the peak, the cap cloud formed. On the lee side, the air wequipped as it descended back dvery own the slope and the cloud dissipated. The potential for solid disturbance is absolutely existing as soon as a cloud prefer this has created.

Rotor, or roll clouds (below) might be developed at roughly the elevation of the mountain height. Roll clouds are developed by the rotor circulation of air on the leeward side of the mountain below the wave crests - see the over diagram. This is the area of the biggest hazard because of the extreme disturbance in and listed below rotor clouds.


Images from: University of Coloracarry out at Boulder Georgraphy Department


Finally, you might see standing lenticular clouds equivalent to those that appear at the start of this article and also to the left. Standing lenticular clouds are lens shaped clouds, hence their name.

Standing lenticular clouds form in the crests of the mountain wave where the increasing updraft of the wave has cooled and moisture has actually condensed. The clouds dissipate in the downdrafts of the wave where the air has actually descended and wequipped to the suggest wright here the moisture evaporates and is no much longer visible. This is why the clouds are dubbed “standing”. They remain in the crests of the hill waves and execute not relocate with the wind flow.

Even standing lenticular clouds are classified by their altitude. You might respeak to that clouds are grouped right into 4 families: Low, Center, High, and also Clouds through comprehensive vertical breakthrough.

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With respect to standing lenticular clouds, they are cumulidevelop clouds by nature and are thought about middle (altocumulus standing lenticular) and high (cirrocumulus standing lenticular), for this reason the abbreviations ACSL and CCSL in the diagram over.

Points to remember

A few items to keep in mind as you begin training to fly in hills (or examine for a knowledge exam): Mountain flying is a skill that should be learned. Find a qualified instructor. Don"t just tread out on your very own having actually read a book - or a newsletter! Anytime that winds blow throughout a mountain at speeds of 25 to 40 knots, the potential for moderate disturbance exists. Winds that exceed 40 knots can produce significant or higher turbulence Stable air produces a hill wave, and also the disturbance deserve to be unpleasant at best, and catastrophic at worst. The strongest, most dangerous disturbance associated through a hill wave is on the lee side of the mountain in and under rotor clouds. In hill wave problems, turbulence will constantly be current, however clouds might not be! So, simply because you don’t view clouds does NOT expect that the turbulence is not tright here. You cannot count on seeing clouds to identify and also predict turbulence, but if you see standing lenticular clouds, roll or roll clouds or a cap cloud, you know the disturbance is there! Mountain wave connected clouds and disturbance can extend downrange for more than 100 miles!