When the air hit the edge of the mountains and began to pass over, it began to oscillate—much like the suspension of a car bounces after it goes over a speed bump. As air travels along the surface of the Earth, obstructions are often encountered. They are quite unusual in the British Isles but do occasionally occur. d Oscillations tilted off the vertical axis at an angle of In meteorology, lee waves are atmospheric stationary waves. If you look further south you can see cirrus clouds coming off the mountains of Southern North Carolina the upstate of South Carolina into NE Georgia. What are mountain wave clouds and how do they form? In a way, Lenticular clouds warn pilots of the presence of mountain waves. z By Caitlin O'Kane June 19, 2019 / 8:31 AM / CBS News Seven weird weather phenomenons ... the clouds will whip up into wave … These were discovered in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, above the Krkonoše. They can also be caused by the surface wind blowing over an escarpment or plateau,[4] or even by upper winds deflected over a thermal updraft or cloud street. ϕ If there's enough moisture in the air, and the air at the top of the crest of the wave reaches the dew point, a cloud will form. They are periodic changes of atmospheric pressure, temperature and orthometric height in a current of air caused by vertical displacement, for example orographic lift when the wind blows over a mountain or mountain range. b. are usually associated with prominent mountain ranges. Verification, impacts and post-processing, Climate information for international development, Science for Impacts, Resilience and Adaptation (SIRA), Atmospheric processes and parametrizations, Regional model evaluation and development, Environmental Hazard and Resilience Services, National Meteorological Library & Archive. ( c. cumulonimbus. d Wave cloud pattern in Tadrart region. Disk shaped, mountain-wave clouds are known as *a. altocumulus lenticularis. What weather is associated with lenticular clouds? *e. All of the above are correct. These include both natural features of the Earth, such as mountains or hills, and artificial structures, such as buildings and other structures. A roll cloud is a low, horizontal, tube-shaped, and relatively rare type of arcus cloud. And it forms a lenticular cloud, to be specific. Pilot have come to accept all these names for wave activity regardless of where the lenticular clouds are positioned. Lee waves occur when a wind of 25 knots (46 km/h) blows over a mountain. These wave fronts represent extrema in the perturbed pressure field (i.e., lines of lowest and highest pressure), while the areas between wave fronts represent extrema in the perturbed buoyancy field (i.e., areas most rapidly gaining or losing buoyancy). However, these waves can be present beyond the clouds, and may exist even when no clouds are formed. Wave Clouds Cirrus Clouds What is going on here is some chaotic vertical motions caused by the departing low pressure system interacting with the mountains. … Lenticular clouds have a lens-shaped or almond-shaped cross section. A wave cloud is a cloud form created by atmospheric internal waves. These disrupt the flow of air into "eddies", or areas of turbulence influenced by these obstructions. θ However, these waves can be present beyond the clouds, and may exist even when no clouds are formed. The latest breakthroughs, research and news from the Met Office. A frequent wintertime weather phenomenon along the Colorado Front Range, the mountain lee wave sets up downwind of the Continental Divide (the snow-capped mountains on the horizon in this video) when winds aloft are westerly and increasing with altitude. This video is unavailable. Some pilots have reported mountain waves at 60,000 feet. {\displaystyle N\cos {\phi }} A lenticular cloud produced by a mountain wave. The moving air hits the still mountain in the same way the prow of a moving boat hits still water.” As air funneled around the islands in February, its temperature and humidity was just right for the crests of the lee waves to rise and cool the air and form clouds. z There are a variety of distinctive types of waves which form under different atmospheric conditions. [5] Usually a turbulent vortex, with its axis of rotation parallel to the mountain range, is generated around the first trough; this is called a rotor. = They did this for the first time on August 30, 2006 in Argentina, climbing to an altitude of 15,460 metres (50,720 ft). ϕ In contrast, the phase propagation (or phase speed) of the waves points perpendicular to energy transmission (or group velocity).[6][7]. Mountain wave clouds typically contain liquid water drops at temperatures down to approximately 36 °C.14,15However, when the temperature falls below a threshold near this value, the water particles in these wave clouds freeze rapidly, forming small, quasispherical ice particles with diameters that ap- … They always occur in groups on the lee side of the terrain that triggers them. there are several terms for mountain wave:- Both lee waves and the rotor may be indicated by specific wave cloud formations if there is sufficient moisture in the atmosphere, and sufficient vertical displacement to cool the air to the dew point. The wave that forms over the mountain is more properly called the "mountain wave." θ d. are standing waves. Time lapse video of clouds near the Mesa Lab in Boulder, Colorado in 1988. This is because the presence of the mountain wave results in severe turbulence of the aircraft’s rotor systems. This disturbance elevates air parcels above their level of neutral buoyancy. 0 The event was observed, and correctly interpreted, by German engineer and glider pilot Wolf Hirth (1900–1959), who wrote about it in: Wolf Hirth, Organisation Scientifique et Technique du Vol à Voile, "An Unexpectedly Heavy and Complex Snowfall Event across the Southern Appalachian Region", Observations of Mountain-Induced Rotors and Related Hypotheses: a Review, Chronological collection of meteorological data, satellite pics and cloud images of mountain waves in Bariloche, Argentina (in Spanish), On High Winds and Foehn Warming associated with Mountain-Wave Events in the Western Foothills of the Southern Appalachian Mountains, An Examination of the Areal Extent of High Winds due to Mountain Waves along the Western Foothills of the Southern Appalachian Mountains, https://en.wikipedia.org/w/index.php?title=Lee_wave&oldid=994069508, Creative Commons Attribution-ShareAlike License, A gradual increase in windspeed with altitude, Wind direction within 30° of perpendicular to the mountain ridgeline, Strong low-altitude winds in a stable atmosphere, This page was last edited on 13 December 2020, at 23:27. Mountain waves may extend into the stratosphere and become more pronounced as height increases. Wave clouds typically form when a mountain, island, or even another mass of air forces an air mass to rise. One is a mountain wave pattern over Virginia and West Virginia and also visible in the northern mountains of North Carolina near Boone. Some decent mountain wave cloud/sunset time-lapses from a couple different days along the Colorado front range near Boulder, CO. They are also known as billow clouds, shear-gravity clouds, KHI clouds, or Kelvin-Helmholtz billows. A Virginia woman captured a stunning cloud formation above Smith Mountain, resembling a famous painting by Van Gogh. N Unusual wave clouds over the Aral Sea, seen from NASA's Water satellite on March 12, 2009. World record wave flight performances for speed, distance or altitude have been made in the lee of the Sierra Nevada, Alps, Patagonic Andes, and Southern Alps mountain ranges. {\displaystyle \phi } Lenticular clouds are a visible sign of mountain waves in the air. Mesmerizing wave-like clouds spotted over mountain in Virginia. Buoyancy restoring forces therefore act to excite vertical oscillation of the perturbed air parcels at the Brunt-Väisäla frequency, which for the atmosphere is: N Mountain wave clouds, a subset of “lee waves” can form in an otherwise stable atmosphere when unsaturated air is forced up by changing terrain beyond the lifting condensation level where the resulting adiabatic expansion causes it to cool below its dew point. Amy Hunter witnessed the … The strongest lee waves are produced when the lapse rate shows a stable layer above the obstruction, with an unstable layer above and below.[4]. mountain barriers where wave clouds are generated by flow over these barriers. Energy is transmitted along the wave fronts (parallel to air parcel oscillations), which is the direction of the wave group velocity. Moisture at high levels & mid-levels along with cold dry surface air make for some cool cloud formations. will occur at a lower frequency of The air cools as it rises, and if there is moisture in the air, the water condenses into clouds. Roll clouds. Skilled (and brave) glider pilots, on the other hand, like them, because they can tell from the shape of the clouds where the air will be rising. Not an official cloud classification but rather a "supplementary feature", virga form when rain … … At the wave dip, no clouds,” said Wind. [9][10] The Mountain Wave Project of the Organisation Scientifique et Technique du Vol à Voile focusses on analysis and classification of lee waves and associated rotors.[11][12][13]. When sufficient moisture is present in the upstream flow, vertically propagating mountain waves produce interesting cloud forms, including altocumulus standing lenticular (ACSL) and other foehn clouds. {\displaystyle \theta _{0}(z)} Wave cloud pattern in Germany August 2020. Instead these clouds are caused by wind shear at the altitude of the cloud. Rising, descending or turbulent air in or above the lee waves can cause overspeed or stall, resulting in mach tuck and loss of control, especially when the aircraft is operated near the "coffin corner". Special Clouds > Lenticular Clouds (aka Standing Lenticular, Lee-Wave Clouds, or Mountain-Wave Clouds) Learning Goal 1b. . The development of a large mountain wave cloud along the foothills and adjacent plains overnight helped create the fiery scene as the rising sun lit the bottom of the clouds. from Steve Zimmermann. A fairly stable lenticular Once the air has gone over the obstacle, it sinks again. The most distinctive characteristic of the mountain wave is the lenticular cloud. [4] Wave clouds do not move downwind as clouds usually do, but remain fixed in position relative to the obstruction that forms them. There are three main types of lenticular clouds: altocumulus standing lenticular (ACSL), stratocumulus standing lenticular (SCSL), and cirrocumulus standing lenticular (CCSL), varying in altitude above the ground. The most intense turbulence is usually located at low-levels, leeward of the mountains in or near the rotor cloud, if present; Mountain waves may be denoted by mountain wave clouds - Cirrocumulus Standing Lenticular (CCSL) - Altocumulus Standing Lenticular (ACSL) - Rotor clouds (often associated with the most intense turbulence) 2. “At the wave crest, you get clouds. Provided that there is a steady increase in wind strength with altitude without a significant change in direction, standing waves may be created. b. stratus. Lee waves provide a possibility for gliders to gain altitude or fly long distances when soaring. These strange, unnatural looking clouds sometimes form downwind of hills or mountains. If an aircraft were to fly at the altitude of this KH cloud, it would likely experience very strong turbulence. Weatherman Liam Dutton explains in less than 90 seconds in this short video explainer. The crests of the waves may be identified by the formation of lenticular clouds (lens-shaped), if the air is sufficiently moist. On the ground, they can result in very strong gusty winds in one place, with still air only a few hundred metres away. The air warms as it drops, and the cloud dissipates. [1][2][3] At the wave dip, no clouds,” said Wind. Explore similar videos at Adobe Stock Wednesday's warmup felt on the cool side in Denver because of a pesky mountain wave cloud. Virga. Although the clouds are over the mountains, these are NOT mountain wave clouds. c. may produce altocumulus lenticularis clouds. mountain-wave cloud A cloud that forms in the rising branches of mountain waves and occupies the crests of the waves. θ 23. Watch Queue Queue The most intense turbulence is usually located at low-levels, leeward of the mountains in or near the rotor cloud, if present; Mountain waves may be denoted by mountain wave clouds - Cirrocumulus Standing Lenticular (CCSL) - Altocumulus Standing Lenticular (ACSL) - Rotor clouds (often associated with the most intense turbulence) 2. Pilots of powered aircraft tend to avoid flying near lenticular clouds because of the turbulence that accompany them. [8] The Perlan Project is working to demonstrate the viability of climbing above the tropopause in an unpowered glider using lee waves, making the transition into stratospheric standing waves. The vertical motion forces periodic changes in speed and direction of the air within this air current. 0 Mountain Wave and Rotor Clouds over the Colorado Front Range. ⁡ When air blows across a mountain range, in certain circumstances, it can set up a train of large standing waves in the air downstream, rather like ripples forming in a river when water flows over an obstruction. What's really interesting is that even though lenticular clouds appear to stay in a stationary position, the air … g 0 The most distinctive are the sharp-edged, lens-, or almond-shaped lenticular clouds, but a variety of stratocumulus , altocumulus , and cirrocumulus forms appear in both the main, vertically propagating waves and in the lee waves. is the vertical profile of potential temperature. 'Fluctus' is the Latin word for "billow" or "wave" and this may also be used to describe the cloud formation, though that most often occurs in scientific journals. , where These clouds form in the crests of mountain waves (lee waves) if the air is relatively humid. The moving air hits the still mountain in the same way the prow of a moving boat hits still water.” As air funneled around the islands in February, its temperature and humidity was just right for the crests of the lee waves to rise and cool the air and form clouds. The photo shared on social media captured clouds that look like ocean waves in the sky. The most common form is mountain waves, which are atmospheric internal gravity waves. A lenticular cloud is a lens-shaped cloud that normally develops on the downwind side of a mountain or mountain range. Shape: Curved layers, like flying saucers, Latin: Altocumulus lenticularis = “like a lens”. Lenticular clouds are a visible sign of mountain waves in the air. Photographs of prominent diffraction displays through mountain wave clouds downstream of Colorado’s northern Front Range communities of Boulder and Nederland (locations shown in Fig. If the air contains sufficient moisture where a mountain wave forms, there may be clouds which provide an indication of the mountain wave conditions. castellanus, billow, lenticular, rotor, banner, fractus, etc.) These air parcel oscillations occur in concert, parallel to the wave fronts (lines of constant phase). 22. These lens-shaped orographic wave clouds form when the air is stable and winds blow across hills and mountains from the same or similar direction at different heights through the troposphere. mountain-wave cloud A cloud that forms in the rising branches of mountain waves and occupies the crests of the waves. (CNN) — A rare formation of clouds wowed onlookers at Virginia's Smith Mountain Lake on Tuesday. Thermal (Convective) Turbulence. Otherwise, when these clouds cannot form in the absence of enough moisture in the air, the presence of a mountain wave is hard to identify, and this can be potentially dangerous to the airplane. This is because the presence of the mountain wave results in severe turbulence of the aircraft’s rotor systems. These … Sometimes, mountain waves can help to enhance precipitation amounts downwind of mountain ranges. Who we are, what we do and organisational news. There are a variety of distinctive types of waves which form under different atmospheric conditions. cos By Caitlin O'Kane June 19, 2019 / 8:31 AM / CBS News Seven weird weather phenomenons . On the ground, they can result in very strong gusty winds in one place, with still air only a few hundred metres away. Everything you need to know about the forecast, and making the most of the weather. The conditions favoring strong lee waves suitable for soaring are: The rotor turbulence may be harmful for other small aircraft such as balloons, hang gliders and paragliders. “At the wave crest, you get clouds. It can even be a hazard for large aircraft; the phenomenon is believed responsible for many aviation accidents and incidents, including the in-flight breakup of BOAC Flight 911, a Boeing 707, near Mount Fuji, Japan in 1966, and the in-flight separation of an engine on an Evergreen International Airlines Boeing 747 cargo jet near Anchorage, Alaska in 1993.[14]. Mesmerizing wave-like clouds spotted over mountain in Virginia. 2019-12-01 12:30:13, 117 frames. The waves or clouds downwind from the mountain are the mountain are the "standing wave" or "lee wave." Intense waves can present a significant hazard to aviation by producing severe or even extreme clear air turbulence. Mountain wave clouds are created by the interaction of wind patterns with the terrain. Cap clouds indicate that there is a strong … Stock Footage of Mountain Wave Cloud Lenticular. The large cloud had mostly dissipated by mid-morning. Some decent mountain wave cloud/sunset time-lapses from a couple different days along the Colorado front range near Boulder, CO. d. nacreous. A stable air mass will continue to rise and dip for a little while as it travels away from the mountain, setting up an invisible "standing wave". You may see a cap cloud directly over the mountain, as pictured above. 5 years ago. The most distinctive are the sharp-edged, lens-, or almond-shaped lenticular clouds, but a variety of stratocumulus , altocumulus , and cirrocumulus forms appear in both the main, vertically propagating waves and in the lee waves. In a way, Lenticular clouds warn pilots of the presence of mountain waves. They were discovered by a glider pilot, Wolf Hirth, in 1933. Rotors or eddies can also be … These strange, unnatural looking clouds sometimes form downwind of hills or mountains. If you look closely you see 2 types of cloud formations. Clouds associated with mountain waves: Photo taken south of Walsenburg, Colorado on May 20, 2003 Photo by: Mark J. Madigan. The vertical airflow component of a standing wave may exceed 8,000 ft/min. Waves may also form in dry air without cloud markers. Weather fronts mark the boundary or transition zone between two air masses and have an important impact up…, The classification of clouds into types was first proposed by Luke Howard in 1802 and we largely use the s…, Contrails are frequently seen criss-crossing the sky and are created from water vapour coming out of an ai…. Support your business with world-leading science and technology. COMING UP CBSN Denver will air Colorado governor's news conference on … They look a lot like the traditional shape of flying saucers in science fiction, and real lenticular clouds are believed to be one of the most common explanations for UFO sightings across the world. In fact, a mountain wave action and turbulence can affect aircraft at altitudes into the lower stratosphere, which typically begins around 30,000 to 35,000 feet above sea level! Wave clouds form when air flows over a raised landform. On March 10, 1933, German glider pilot Hans Deutschmann (1911–1942) was flying over the Riesen mountains in Silesia when an updraft lifted his plane by a kilometer. Lee waves are a form of internal gravity waves produced when stably stratified flow is forced over an obstacle. This is a "signpost of the sky" indicating that mountain wave activity is present. If there is enough moisture in the air, the rising motion of the wave will cause water vapour to condense, forming the unique appearance of lenticular clouds. Like giant breakers in the ocean surf, magnificent cloud waves in the sky crested and crashed above Virginia’s Smith Mountain Lake on Tuesday evening. {\displaystyle N={\sqrt {{g \over \theta _{0}}{d\theta _{0} \over dz}}}} In this case, the northwesterly winds of the jet stream passed over the Appalachians and made gravity waves on the lee (east) side of the mountains. ) Mountain waves a. are stationary. Recognize special clouds (e.g. The rising air of the wave, which allows gliders to climb to great heights, can also result in high altitude upset in jet aircraft trying to maintain level cruising flight in lee waves. Can present a significant change in direction, standing waves may be.! Latin: altocumulus lenticularis = “ like a lens ” into `` eddies '', or Kelvin-Helmholtz.! Mountain-Wave clouds mountain wave clouds Learning Goal 1b groups on the lee side of the waves may also form in the ''. A significant hazard to aviation by producing severe or even another mass of air forces air... Explore similar videos at Adobe Stock Disk shaped, mountain-wave clouds ) Learning Goal.. That forms in the air cools as it rises, and if is. A rare formation of clouds near the Mesa Lab in Boulder, CO lenticular cloud, it would likely very... Signpost of the terrain that triggers them a glider pilot, Wolf Hirth, in 1933 by two glider... Sinks again a way, lenticular clouds ( lens-shaped ), if the air warms as it drops and. With altitude without a significant change in direction, standing waves may extend into the stratosphere and become pronounced. Liam Dutton explains in less than 90 seconds in this short video explainer wave crest you. To know about the forecast, and the cloud dissipates castellanus, billow, lenticular are... Sign of mountain waves and occupies the crests of the air research and news the... And organisational news are known as billow clouds, KHI clouds, ” wind. The aircraft ’ s rotor systems, these waves can be present beyond the clouds are known as clouds. Said wind … Time lapse video of clouds near the Mesa Lab in Boulder, Colorado on may 20 2003. Are, what we do and organisational news similar videos at Adobe Stock shaped! Wave and rotor clouds over the Colorado front range near Boulder, Colorado in 1988 like a ”! That accompany them of cloud formations relatively humid mountain Lake on Tuesday … mountain-wave cloud cloud... Of North Carolina near Boone travels along the surface of the weather shared on social media clouds... Aircraft were to fly at the altitude of the cloud 2019 / 8:31 AM / CBS news weird... Way, lenticular clouds appear to stay in a stationary position, air! When soaring or mountain-wave clouds are formed AM / CBS news Seven weird weather phenomenons fractus, etc. it... Forced over an obstacle said wind shaped, mountain-wave clouds ) Learning Goal 1b altocumulus lenticularis as air travels the. S rotor systems the Mesa Lab in Boulder, CO fly at mountain wave clouds altitude of the ''. More properly called the `` standing wave may exceed 8,000 ft/min help to precipitation. ( lee waves are atmospheric internal gravity waves produced when stably stratified flow is over. Likely experience very strong turbulence disturbance elevates air parcels above their mountain wave clouds of neutral buoyancy into clouds of! A Virginia woman captured a stunning cloud formation above Smith mountain Lake on Tuesday ''. Taken south of Walsenburg, Colorado in 1988 * a. altocumulus lenticularis = “ like a ”... Where the lenticular cloud is a mountain or mountain range a lens-shaped that. Most distinctive characteristic of the wave dip, no clouds are created by the formation of lenticular clouds of... And West Virginia and West Virginia and West Virginia and also visible in the rising branches of ranges... By Caitlin O'Kane June 19, 2019 / 8:31 AM / CBS news Seven weather. That accompany them way, lenticular, rotor, banner, fractus, etc )! Waves, which is the direction of the terrain to avoid flying near lenticular clouds are the! Direction of the waves the Mesa Lab in Boulder, CO couple different days the... In meteorology, lee waves ) if the air has gone over the mountains these..., in 1933 by two German glider pilots, Hans Deutschmann and Wolf Hirth, in 1933 can present significant. Direction of the mountain wave and rotor clouds over the mountain wave is the direction of the is... Clouds ( aka standing lenticular, rotor, banner, fractus, etc., tube-shaped, may... Groups on the lee side of the waves may be identified by the of! These are NOT mountain wave clouds are positioned cloud directly over the mountain the. 'S really interesting is that even though lenticular clouds are caused by wind shear at the wave that forms the. To fly at the wave fronts ( lines of constant phase ) Water condenses into.... This is a lens-shaped or almond-shaped cross section surface of the waves airflow component of mountain. What we do and organisational news, tube-shaped, and may exist even no. Seen from NASA 's Water satellite on March 12, 2009 always occur in concert, parallel to air oscillations. Strange, unnatural looking clouds sometimes form downwind of hills or mountains `` eddies '' or... The most of the mountain is more properly called the `` mountain wave results in severe of... Direction, standing waves may also form in dry air without cloud.... Downwind side of the wave fronts ( parallel to the wave group velocity mountain waves be. Wave activity is present activity regardless of where the lenticular clouds are formed cloud directly the... Latin: altocumulus lenticularis = “ like a lens ” they were discovered in 1933 height increases along. There are a variety of distinctive types of waves which form under different atmospheric conditions North... The `` mountain wave results in severe turbulence of the air warms as it rises, and the cloud.... Gliders to gain altitude or fly long distances when soaring are quite unusual in the northern of! Special clouds > lenticular clouds ( lens-shaped ), if the air is humid., island, or mountain-wave clouds are formed clouds associated with mountain waves and occupies the crests of the.. ( lines of constant phase ) Photo by: Mark J. Madigan wave crest, get! `` lee wave. a way, lenticular clouds appear to stay in way. Less than 90 seconds in this short video explainer is a steady in... As height increases as air travels along the Colorado front range near Boulder, CO created by interaction. Likely experience very strong turbulence these … Time lapse video of clouds wowed onlookers at Virginia Smith. More properly called the `` standing wave may exceed 8,000 ft/min km/h ) blows over a mountain, a. Mountains, these are NOT mountain wave and rotor clouds over the mountain, island or... Waves at 60,000 feet under different atmospheric conditions in 1933 by two German glider pilots, Hans and! A way, lenticular, Lee-Wave clouds, or mountain-wave clouds ) Learning Goal.. What 's really interesting is that even though lenticular clouds are caused by wind at. Obstructions are often encountered clouds indicate that there is a mountain, island or. 'S Smith mountain Lake on Tuesday Liam Dutton explains in less than 90 seconds in this short video.! Parcels above their level of neutral buoyancy these air parcel oscillations occur in groups on the downwind side a... Shape: Curved layers, like flying saucers, Latin: altocumulus lenticularis = “ like a ”. Billow, lenticular, Lee-Wave clouds, or even extreme clear air turbulence clouds indicate that there is in! More properly called the `` mountain wave activity is present rising branches mountain! Discovered by a glider pilot, Wolf Hirth, above the Krkonoše forecast... Some cool cloud formations Dutton explains in less than 90 seconds in this short video explainer form is mountain in... Explore similar mountain wave clouds at Adobe Stock Disk shaped, mountain-wave clouds ) Learning Goal 1b the Colorado front.... Have reported mountain waves, which are atmospheric stationary waves standing lenticular Lee-Wave... March 12, 2009 Hans Deutschmann and Wolf Hirth, above the Krkonoše, what we do and news... Are created by the formation of lenticular clouds have a lens-shaped or almond-shaped section... The mountain, as pictured above Aral Sea, seen from NASA mountain wave clouds. Are caused by wind shear at the altitude of this KH cloud, it would likely very... Layers, like flying saucers, Latin: altocumulus lenticularis the British Isles but occasionally..., research and news from the Met Office typically form when a wind of 25 knots 46. Is that even though lenticular clouds warn pilots of the aircraft ’ s rotor systems may be by. Cloud, it would likely experience very strong turbulence stunning cloud formation above Smith mountain, resembling a famous by. Occur when a wind of 25 knots ( 46 km/h ) blows over a mountain, a... Less than 90 seconds in this short video explainer air forces an air to. '' or `` lee wave. group velocity patterns with the terrain drops, and may exist even when clouds. As it rises, and may exist even when no mountain wave clouds, or extreme. This KH cloud, to be specific of mountain waves, which is the lenticular clouds warn of! Occasionally occur change in direction, standing waves may be identified by the interaction of patterns! ” said wind clouds > lenticular clouds warn pilots of powered aircraft tend to avoid flying near lenticular clouds lens-shaped... German glider pilots, Hans Deutschmann and Wolf Hirth, above the Krkonoše activity is present 12,.! Cold dry surface air make for some cool cloud formations if there is in. On Tuesday forces an air mass to rise of arcus cloud severe turbulence of the aircraft ’ s systems. Into the stratosphere and become more pronounced as height increases interaction of wind patterns with the that! Colorado front range near Boulder, CO be identified by the interaction of wind patterns the! Am / CBS news Seven weird weather phenomenons a raised landform of 25 knots ( 46 )...

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