Clouds and Precipitation

Alyssa Goodwin

Adiabatic Temperature Changes and Expansion and cooling

• When air is allowed to expand, it cools, and when it’s compressed, it warms.

• Temperature changes that happen even though heat isn’t added or subtracted. It’s the result of compressed air.

• Expansion and cooling happens because there are fewer and fewer gas molecules.

http://apollo.lsc.vsc.edu/~wintelsw/MET1010LOL/chapter06/

Orographic Lifting

• When elevated terrains act as barriers to air flow.

• As air goes up a mountain slop, adiabatic cooling generates clouds and precipitation.

• By the time air reaches the leeward side of a mountain, much of it’s moisture has been lost.

https://fp.auburn.edu/fire/weather_elements.htm

Frontal Wedging

• Warm and cold air collides• Cool, dense air act like a barrier then the

warmer, less dense air rises. • Usually creates rain

https://fp.auburn.edu/fire/weather_elements.htm

Convergence

• When air in the lower atmosphere flows together.

• Air goes up because it cant go down.• This leads to cloud formation.

http://apollo.lsc.vsc.edu/classes/met130/notes/chapter6/lift_converge.html

Localized Convective Lifting

• Unequal heating of the Earth’s Surface• The air above a warmer, dense area will rise• When warm parcels of air rise above

condensation level, clouds form.

http://ww2010.atmos.uiuc.edu/(Gh)/guides/mtr/cld/dvlp/cnvrg.rxml

Stability (Density Differences and Stability and weather)

• Stable air remains in it’s original position, unstable air rises.

• Stable air resists upward movement.• Clouds won’t form when stable air resists

upward movement.

http://www.santabarbara.com/community/weather/

Condensation

• For any of these forms of condensation to occur, the air must be saturated.

• It happens when water vapor changes to a liquid.

• Saturation occurs mostly when air is cooled to its dew point or when water vapor is added to the air.

http://shoalwater.nsw.gov.au/Education/condensation.htm

Types of Clouds

• Clouds are classified by their form and height.• Cirrus-curl of hair, Cumulus-a pile, stratus-a

layer.• All other clouds reflect one of these three

basic form or are combinations or modifications of them.

http://eo.ucar.edu/webweather/cloud3.html

High Clouds

• Cirrus, Cirrostratus and Cirrocumulus.• High clouds are thin and white and often

made up of ice crystals• Low temperatures and small quantities of

water vapor are present at high altitudes.

https://www.meted.ucar.edu/sign_in.php?go_back_to=http%253A%252F%252Fwww.meted.ucar.edu%252Ffire%252Fs290%252Funit6%252Fprint_2.htm

Middle Clouds

• Clouds in the middle range have the prefix alto- as part of their name.

• Altocumulus clouds are larger and denser that Cirrocumulus (high Cloud)

• Middle clouds usually are accompanied by snow or drizzle

https://www.meted.ucar.edu/sign_in.php?go_back_to=http%253A%252F%252Fwww.meted.ucar.edu%252Ffire%252Fs290%252Funit6%252Fprint_2.htm

Low Clouds

• Stratus, Stratocumulus, nimbostratus.• Look like fog-like layers and have vertical

development.• Develop in stable air, because air is forced

upward.

https://www.meted.ucar.edu/sign_in.php?go_back_to=http%253A%252F%252Fwww.meted.ucar.edu%252Ffire%252Fs290%252Funit6%252Fprint_2.htm

Clouds of Vertical Development

• Some clouds aren’t categorized by high, middle, or low, they extend upward.

• Once upward movement is started, acceleration is powerful and clouds with a lot of vertical range form.

• End result is cumulonimbus clouds and rain or thunderstorms.

http://en.wikipedia.org/wiki/Cloud

Fog (by cooling and by evaporating)

• Fog is defined as a cloud with its base at or very near the ground.

• Form on cool, clear, calm nights when the surface is cooled rapidly by radiation.

• Cool air moves over warm water, moisture might evaporate from the water surface to produce saturation.

http://www.kidsgeo.com/geography-for-kids/0110-fog.php

Cold Cloud Precipitation(Bergeron Process)

• Supercooling and supersaturation.• Supercooled air will freeze when it impacts a

solid object.• Ice crystals can’t coexist with water droplets in

air because the air “appears” supersaturated to the ice.

http://www.geo.hunter.cuny.edu/~tbw/wc.notes/5.cond.precip/precipitation/bergeron_process.htm

Warm Cloud Precipitation(Collision-coalescence process)

• Collision-coalescence process is a mechanism that forms raindrops.

• As large droplets move through the cloud, they join with smaller, slower droplets.

• The droplet become bigger from joining.

https://www.meted.ucar.edu/sign_in.php?go_back_to=http%253A%252F%252Fwww.meted.ucar.edu%252Fhydro%252Fbasic_int%252Fflash_flood%252Fnavmenu.php%253Ftab%253D1%2526page%253D2.2.2

Rain and Snow

• Rain means drops of water that fall from a cloud and have a diameter of at least .5 mm.

• Surface temperature above 4°C, flakes melt.• At low temperatures, light and fluffy snow

falls.

http://zahiym5tlc.edublogs.org/

Sleet, Glaze, and Hail

• Sleet-the fall of small particles of clear-to-translucent ice.

• Glaze-known as freezing rain• Hail-produced in cumulonimbus clouds. They

begin as small ice pellets that grow by collecting supercooled water droplets.

http://www.kidsgeo.com/geography-for-kids/0119-hail.php

The End