Weather

Weather Factors• Air Temperature– Molecules always

moving– Measure of the average

amount of molecule motion

– Measured by a thermometer • Temperature high

molecules move more rapidly feels warm

• Temperature low molecules move slowly feels cool

Weather Factors• Wind– Sun warms Earth’s

surface warms air above – air expands & rises low pressure

– Cold dense air sinks high pressure

• CAUSES the wind- air moves from areas of high to low pressure

• Measured by: direction weather vane

weather sock

Speed anemometer

Weather Factors

• Humidity– Measured by a hygrometer

– Warm moist air more vapor moves fast

Molecules

Weather Factors

• Humidity

– Cold air less vapor moves slowly

Because molecules move slowly the water vapor sticks & forms droplets= condensation

Weather Factors

• Relative humidity– Amount of water vapor in air compared to amount

needed for saturation (most it can hold)

Weather Factors

• Air pressure– Weight of air

pressing down on surface

– Measured by barometer

Cloud Formation:

• warm moist air condenses in tiny droplets around dust and salt particles

• Particles remain suspended- billions of these form clouds

Classified by

• Height– cirro = high– alto= middle– strato= low– example• cirrostratus= high layer of stratus clouds• Altocumulus=middle layer of cumulus clouds

Explain what stratus clouds look like:

Classified by:

• Shape– Stratus – smooth even sheets (layers) Low altitudes

Fair weather Fog= stratus cloud near ground

Describe cumulus clouds:

• Cumulus-– puffy white with flat bases

Fair weather

Describe Cirrus Clouds:

• Cirrus- – high thin white feathery

Made of ice crystals– Fair weather– Signals approaching storms

Describe nimbostratus

Rain clouds

• Nimbus = dark• Nimbostratus– dark layered clouds– long steady rain/snow

Describe cumulonimbus clouds

Rain clouds

• Cumulonimbus– dark puffy clouds – thunderstorms

Precipitation• Cloud droplets grow large enough to fall• Type determined by temperature

Rain

• Water falling in temperatures above freezing (32°)

Above 32°

Snow

• Water falling in freezing temperatures that vapor changes directly to solid

Below 32°

sleet

• Rain passes through freezing temps near Earth’s surface forming ice pellets

Above 32°

Below 32

Hail• Water drops freeze in layers around small

nuclei of ice in cumulonimbus clouds during a thunderstorm grow larger by being tossed up and down by air in clouds