A Quick Introduction to Clouds

Lis Cohen

liscohen@met.utah.edu

www.WeatherOutreach.org

Cloud Naming

• Cloud naming is based on four cloud characteristics and three cloud levels

• There are about 30 distinct cloud types

• Professionals may use 10, a casual observer 3 or 4

Cloud Characteristics

• Cirrus– Fiber or Hair

• Cumulus– Heaped or Piled

Cloud Characteristics

• Stratus– Sheet or Layer

• Nimbus– Rain Making

Cloud Levels

• High Cumulus– Size of top of thumb

at arms length

• Low Cumulus– Size of fist at arms length

Photo: WBZ-Mos

Cloud Levels

• High Stratus– Sun and Moon easily seen

• Low Stratus– Sun and Moon difficult to see

Cloud LevelsHigh Clouds

• Generally form above 20,000 feet• Usually appear white, except for sunrise/set• Usually thin and composed almost exclusively

of ice crystals

Cloud LevelsHigh Clouds

Indicative of upper level moisture

(storms possible in 6-24 hours).

Cloud LevelsHigh Clouds

• CIRRUS

• CIRROSTRATUS

• CIRROCUMULUS

Photo: WBZ-Mos

Cloud LevelsMiddle Clouds

• Cloud bases are located between 6,500-23,000 feet in the mid-latitudes

• Composed of water droplets and when temperatures are low enough, some ice crystals

Cloud LevelsMiddle Clouds

• ALTOSTRATUS

• ALTOCUMULUS

ALTOCUMULUS

Possible marker of PM t-storms when seen in the AM with greater vertical development.

(Clouds form in unstable air with stable air above them.)

Cloud LevelsMiddle Clouds

Cloud LevelsLow Clouds

• Cloud base lies below 6,500 feet• Almost always composed of water droplets,

but in cold weather, may contain ice particles and snow

Cloud LevelsLow Clouds

• Stratus

• Stratocumulus

• Nimbostratus

Museum of Science/WBZ conference

Cloud LevelsLow Clouds

• Can form drizzle like precipitation• Often stable layer is found above these clouds

Cloud LevelsLarge Vertical Development

• CUMULUS

• CUMULONIMBUS

• Cumulus Humulis

• Cumulus Fractus

Cloud LevelsLarge Vertical Development

Photographer: Unknown

Photographer: Unknown

• Cumulus Congestus

• Cumulonimbus Incus

Cloud LevelsLarge Vertical Development

Photographer: Unknown

Photographer: Unknown

• Occurs with an unstable atmosphere

• Often indicative of thunderstorms and heavy rain

Cloud LevelsLarge Vertical Development

Unique Clouds

• Lenticular Clouds

• Pileus Clouds

Photographer: Unknown

Photographer: Jay Shafer

Unique Clouds

• Mammatus Clouds

• Condensation Trail or Contrail

Photographer: Unknown

Common Cloud Types

Description of Sky Conditions

• SUNNY OR CLEAR less than 1/10 sky

covered by clouds

• PARTLY CLOUDY/ PARTLY SUNNY

1/10 to 5/10 of sky is covered by clouds

Description of Sky Conditions

• MOSTLY CLOUDY (MOSTLY SUNNY)

6/10 to 9/10 of sky

is covered by clouds (sun)

• OVERCAST

more than 9/10 of the sky is covered in clouds

Undercast

Cloud Naming