High clouds

• >23,000 ft.• cirr- (“curl of hair”)• ice crystals• generally occur in fair weather and point in

direction of air movement at their elevation

• Cirrocumulus: clouds in long rows of puffy clouds; often precursor to precipitation

“mackerel sky”

cirrocumulus

Cirrostratus

• Broad layer of air lifted by large scale convergence; transparent enough to see sun or moon

• “halo” may form from refraction of light by ice crystals

• will thicken and lower if warm front is approaching

cirrostratus

halo

Middle Clouds

• 6500-20,000 ft.• alto-• ice crystals and water droplets

Altocumulus• can be parallel bands or

rounded masses; can distinguish from cirrocumulus because part of them is usually shaded

• form by convection in an unstable layer aloft

• may suggest an approaching cold front

• Hold hand at arm’s length, clouds are thumbnail size

altocumulus

Altocumulus

altocumulus

Altostratus• Absence of shadows

• Sun or moon is bright spot behind clouds, no halo

Low Clouds

• <6500 ft.• strat-• water droplets

nimbostratus

stratocumulus

• Low, lumpy layer of rounded masses, rolls, sometimes with clear sky between

• Hold hand at arm’s length, clouds are fist-size

Cumulonimbusvertically developed