MICHAEL DAVIS PHD CANDIDATE THE OHIO STATE UNIVERSITY Clouds

Altocumulus (Ac) Midlevel m ( ft) Appear in either masses or rolls and are similar to cirrocumulus but the masses are usually larger and darker Normally signal convection and will take on a wavy sheet-like appearance Occur before a cold front and may signal thunderstorm development later in the day

Altostratus (As) Midlevel m ( ft) Appears as a gray sheet and is typically lighter than nimbostratus but darker than cirrostratus The sun may be seen through the cloud and appear as a ‘bright spot’ Formed by the elevated condensation of an air mass usually a frontal system and can be very expansive May produce very light rainfall

Arcus A low level cloud usually on the front edge of a thunderstorm with the outflow boundary 2 types of arcus clouds: Shelf cloud – low wedge shaped cloud that is attached to the thunderstorm Roll cloud – detached, tube shaped cloud that appears to roll along a horizontal axis

Cirrocumulus (Cc) High level m ( ft) Convective environment and composed primarily of ice and supercooled water droplets. Generally short lived as they may evaporate or precipitate as virga in either rain or snow Patterns may look like fish scales so sometimes called “mackerel sky”

Cirrostratus (Cs) High level m ( ft) Thin and mostly composed of ice crystals May produce an ice halo as seen in photo Possible indication of upper level moisture Form in front of warm fronts and rain may be expected in the next hours

Cirrus (Ci) High level m ( ft) Thin and wisplike, sometimes called mare’s tails Composed of ice crystals Can indicate wind shear based on the streaks Cover approximately 30% of the Earth and warm the planet via IR absorption Usually indicate a change in the weather in the near future or blow off from a thunderstorm

Contrails Artificial clouds created by passing aircraft exhaust As hot exhaust is expelled from the engine, the water vapor freezes quickly in the surrounding cold air and forms ice in trails Time duration is highly variable May act to warm the planet by trapping outgoing longwave radiation

Cumulonimbus (Cb) Vertical m ( ft) Tall cloud that signifies the presence of an intense thunderstorm Can form alone, in clusters, or along a cold front Form from convection and strong updrafts which elevate the cloud top to the tropopause Jet stream shears the top creating an anvil like appearance

Cumulus (Cu) Low to mid level Below 2000 m (Below 6500 ft) Appears as heaps and may form alone, in lines, or in clusters Often precede other types of clouds as they encompass a large variety of cloud types Forms when warm air rises and condenses May appear flat bottomed if at the lifted condensation level or form ‘cloud streets’ in a windy environment

Cumulus Congestus (TCu) Vertical Up to 6000 m (up to ft) Form in unstable conditions usually undergoing convection May appear like broccoli Usually signal the progression from cumulus to cumulonimbus

Fog Ground level Low level cloud that reaches the ground resulting in a decrease in visibility Forms when saturation occurs and little wind Many different types of fog Grand Banks, Newfoundland is recognized as the foggiest place in the world averaging 200 days of fog annually

Kelvin- Helmholtz High level Cirrus like Forms when there is a stark difference in velocities between two layers of fluid (remember, the atmosphere is a fluid!) This causes motion between two stratified layers creating a shallow layer of instability

Lenticular Mid level m ( ft) Lens shaped cloud typically forming over areas of orography Forms when stable moist air flows up the orography, creating standing waves on the leeward side. If the temperature reaches the dew point and condenses, a lenticular cloud forms They may be mistaken for UFOs

Mammatus Low level Forms on the underside of a violent thunderstorm and through descending air Sometimes called a breast cloud May appear as smooth, ragged, or lumpy lobes averaging 1-3 km wide and lasting minutes

Nimbostratus (Ns) Low level Below 3000 (Below ft) Appears uniform and dark Will be precipitating as ‘nimbo’ is Latin for precipitation. If not, then it is stratus Precipitation is moderate to heavy and may last for several days

Pileus Sometimes called a scarf cloud or cap cloud Horizontal cloud that appears on top of cumulus or cumulonimbus Formed by strong updrafts uplifting moist low levels causing the air to cool to the dew point as it ascends Indicates strong updrafts as they tend to be associated with thunderstorms

Stratocumulus (Sc) Low level Below 2400 m (8000 ft) Appear rounded, dark masses that usually form in lines or clusters Weak updrafts and dry, stable air above keep clouds low Don’t usually precipitate but can produce light rain or snow. However, they are seen at either the front or end of thunderstorms

Stratus (St) Low level Below 2000 m (Below 6000 ft) Horizontal uniform gray layer of clouds that looks like a bed sheet Usually obscure the sky thus blocking out the sun Essentially above the ground fog