Billow clouds are produced by Kelvin-Helmholtz instability and are also referred to as cloud streets.
WxClds14a_19 		Cattails below and Kelvin-Helmholtz wave clouds above - the clouds are formed by wind shear and any planes flying nearby would likely feel a few moderate bumps of turbulence.
WxClds12b_36 		A rotor cloud resembles a long cigar and is oriented parallel to the mountain ridge - it is also very likely that any aircraft flying through one (or nearby) would experience some rough turbulence.
WxClds15e_22
Wanna scare a few pilots? Ask them if they'd consider flying upon viewing a cloud feature such as this.
WxClds2626_047 		At sunset, the most spectacular display of mammatus I have ever seen is underlit revealing every pocket of cloud shaped like breasts (which is where the name mammatus comes).
WxClds08a_10 		Mammatus clouds beneath a thunderstorm anvil while we chase in a vehicle with meteorological instruments used as part of the VORTEX project.
WxClds01c_14
The next time Chicken-little says the sky is falling, I might believe it. Low hanging mammatus clouds with rain and hail falling out of the back side of this summer thunderstorm (cumulonimbus).
WxClds01b_25 		Altocumulus Lenticular cloud above Crested Butte Mountain (12,162 ft).
WxClds16d_34 		Wave clouds downwind of the Rockies are touched by scarlet red setting sun above a Longmont church (Latter-Day Saints).
WxClds10b_26
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    Weather Gallery (Page 2 of 6)
  1. Cloud basics
  2. Cloud-specifics
  3. Optical Phenomenon
  4. Supercell Thunderstorms
  5. Tornadoes
  6. Lightning
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Cloud-specifics:
 If you're looking for a very bumpy and turbulent ride on an airplane, then you would want to fly on days with clouds that look like these. Most of these cloud photos are associated with a turbulent atmosphere, especially the one referenced by WxClds2626_047. In this photo, the cloud drops act as a tracer revealing the air currents which are otherwise invisible. Here you can see an eddy, or whirlpool, circulating a full 360 degrees. Similarly, the cloud shapes shown in the first three photos are indicative of wave-like undulations of air currents made visible by cloud. The first two are indicative of wind shear (a change in wind direction and/or speed with altitude) and are often called Kelvin-Helmhotz wave clouds. The last one in the first row is called a rotor cloud and indicates a circular moving air current - this one caused by the mountains to the west.
   The paragraph above discussed turbulence caused by wind shear; another source of a turbulent atmosphere is convection. The next three photos are associated with convection. They all show mammatus clouds (the term derives from mamma or mammary glands and I think it's clear why considering these clouds look like breats). In the photo referenced by WxClds08a_10 these clouds were like an umbrella over my head stretching across 50% or more of the whole sky. It was truly an amazing site.
   The mountain photo in the bottom row (table above) shows a type of wave cloud called altocumulus lenticular which have been mistaken for UFOs in the past. They often look like a stack of pancakes or plates and are created by moist air flowing over mountains. If conditions are just right, there can be successive lenticular clouds as air rises, then descends downwind of a mountain range, then rises again to form a second cloud farther downwind. Then, as the sun sets, the bottom of these clouds turn scarlet red as in the last photo (table above).
 
Cloud-Chart:
Cirrus Cirrus clouds (specifically billow clouds).
Cirrus (billows) 		Cirrus and 22° halo.
22° halo 		A cumulus cloud capped by a pileus cloud.
Pileus 		A supercell thunderstorm with anvil.
Thunderstorm anvil
Stratus Stratus cloud underlit by the rising sun.
Stratus 		Stratus clouds in contact with the ground: fog.
Stratus (fog) 		Stratocumulus clouds.
Stratocumulus 		Sun shining through a rain curtain
Rain curtain
Cumulus Cumulus cloud bubbles upward.
Cumulus 		Cumulonimbus anvil with mammatus.
Mammatus 		Cumulonimbus (cumulus cloud that is raining).
Cumulonimbus 		A cap cloud covers a mountain.
Cap cloud


Weather Gallery (Page 2 of 6): Cloud-specifics
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