Cloud Classification and Identification

Part of Chapter 5

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• Cloud classification is based on:‒ Height‒ Physical appearance

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Types of clouds• Clouds with vertical development• Low clouds‒ base below 2,000 m (6,500 ft)‒ composed of water droplets

• High clouds‒ base generally above 6,000 m (20,000 ft)‒ composed of ice crystals

• Middle clouds‒ in between• Some overlap with high clouds

‒ composed of water droplets • (mixed with ice crystals when T is low enough)

• Unusual clouds

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Cloud namesVertically-Developing(Cu) cumulus(Cb) cumulonimbus

Low High Middle(St) stratus (Ci) cirrus(Ns) nimbostratus (Cs) cirrostratus (As) altostratus(Sc) stratocumulus (Cc) cirrocumulus (Ac) altocumulus

UnusualLenticular, mammatus, billow, contrail, others…

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1. Clouds with vertical development

• Cumulus

• Cumuloniumbus

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• Cumulus‒ Abbreviation Cu‒ White-gray puffy clouds• Cumulus‒ Latin for heap or accumulation

‒ Composition: water droplets‒ Scud (Cumulus Fractus)• Irregular and ragged looking• Sometimes form under precipitating clouds

‒ Cumulus Congestus• Towering cumulus

‒ Commonly form by convection• During warm afternoons

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• Cumulonimbus‒ Thunderstorm cloud• Nimbus ‒ Latin for rain

‒ Abbreviation Cb‒ Dark base, commonly anvil shaped‒ Usually extends to top of troposphere‒ Composition varies with height• Water droplets to mix to ice

‒ Lightning and thunder‒ Heavy precipitation• Showery• Capable of rain, snow, hail

‒ Need unstable environments to form• Normally conditionally unstable environment, since absolutely unstable does not occur too often

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Formation of a cumulus cloud

• As the day progresses, conditionally unstable conditions reach higher levels, allowing the cloud to grow‒ From cumulus humilis (regular, small, puffy cloud), to cumulus congestus, to comulonimbus

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2. Low Clouds‒ base below 2,000 m (6,500 ft)‒ composed of water droplets

• Stratus

• Nimbostratus

• Stratocumulus

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• Stratus‒ Abbreviation St‒ Covers entire sky• Stratus ‒ Latin for layer

‒ Resembles fog above the ground‒ No precipitation‒ Cannot see sun through it

‒ Technically, fog is a stratus cloud on the ground

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• Nimbostratus‒ Abbreviation Ns‒ Steady precipitation• Nimbo ‒ rain• stratus ‒ layer

‒ Commonly accompanied by Scud

‒ Sometimes considered a middle cloud• Since it extends from low to middle levels

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• Stratocumulus‒ Abbreviation Sc‒ Lumpy cloud layer‒ Blue sky visible in between‒ Individual “lumps”• Roughly size of fist when arm extended

‒ Produced by an unstable layer capped by a stable layer• Usually an inversion

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3. High Clouds‒ base generally above 6,000 m (20,000 ft)‒ composed of ice crystals

• Cirrus

• Cirrostratus

• Cirrocumulus

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• Cirrus‒ Abbreviation Ci‒ Thin, wispy, feathery clouds• Cirro ‒ Latin for feather

‒ Associated with fair weather

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• Cirrostratus‒ Abbreviation Cs‒ thin, sheet-like clouds that cover the whole sky‒ Sun easily visible through‒ Can be accompanied by a halo

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• Cirrocumulus‒ Abbreviation Cc‒ Small rounded white puffs‒ Less common than Ci and Cs‒ Can resemble fish scales• Mackerel sky

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4. Middle Clouds‒ in between ‒ 2,000 m to 7,000 m• 6,500 ft to 23,000 ft• Some overlap with high clouds

‒ composed of water droplets • (mixed with ice crystals when T is low enough)

• Altostratus

• Altocumulus

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• Altostratus‒ Abbreviation As‒ Covers entire sky‒ Sun dimly seen though it• No shadows cast

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• Altocumulus‒ Abbreviation Ac‒ Grey/white puffy masses‒ Individual “lumps”• Size of thumbnail when arm extended

All Together!

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Hints to help remember names

• “cirro”• Means “feather”• Always used for high clouds

• “alto”• Means “tall”• Always used for middle clouds

• “stratus”• Means “layer”• usually cover entire sky

• “cumulus”• Means “accumulation”• Puffy, rounded

• “nimbus”• Means “rain”• Used for precipitating clouds

• Latin origin

Distinguishing between Sc, Ac and Cc

• Refer to notes from class

Distinguishing between St, As and Cs

• Refer to notes from class

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Distinguishing between St and Ns

• Stratus ‒ no rain

• Nimbostratus - rain

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Note about precipitating clouds• By definition, Cb and Ns cause precipitation‒ Cb ‒ showery, potentially intense‒ Ns ‒ steady, light or moderate

• But other cloud types are also capable of producing some precipitation‒ Mostly drizzle or very light rain or snow

‒ The following table shows what kind of precipitation is possible

32• From “The Cloudspotter’s Guide” (2006)‒ (The symbols refer to precip type and not intensity)

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More to Classification

• There is a lot more to cloud classification

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Guide (2006)

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• Cloud ID Handout

• Cloud type list and links from Wikipedia• (they are slowly being filled up)

‒ http://en.wikipedia.org/wiki/Cloud_types

• Cloud Classification information from the glossary of Meteorology‒ http://amsglossary.allenpress.com/glossary/search?id=cloud-classification1

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• Cloud symbols can be added to the station model• http://www.srh.weather.gov/srh/jetstream/synoptic/wxmaps.htm

‒ All cloud symbols• http://www.srh.weather.gov/srh/jetstream/synoptic/clouds_max.htm

» (click on the pictures)

• High clouds• Middle clouds

• Low Clouds

• Cloud base in hundreds of feet

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5. Unusual clouds‒ Note: Unusual clouds can usually be classified into one of the main ten categories

• Lenticular clouds‒ Individual elements look like a lens‒ More often compared to UFOs

• Billow clouds‒ Look like crashing waves

• Contrails‒ Condensation trails from airplanes

• Clouds outside the troposphere‒ Not a lot is known about them

• Other…

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• Lenticular clouds are wave clouds formed when stable air passes over mountains

• Rising air cools and water vapor condenses into cloud droplets

• Sinking air warms and droplets evaporate

‒ Billow clouds form when two layers of air with differing speeds meet. The wave formation is analogous to waves in the ocean• Also called instability clouds • Or KH-clouds‒ Because formed by Kelvin-Helmholtz instability

Clouds Outside the Troposphere

• Nacreous Clouds

• Noctilucent Clouds

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Nacreousclouds

Noctilucentclouds

http://science.nasa.gov/headlines/y2003/19feb_nlc.htm

Thunderstorm Cloud Features• Mammatus• Overshooting Top• Shelf Cloud• Roll Cloud• Wall Cloud• Cap Cloud

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Other Miscellaneous Clouds

• Cap Clouds• Pyrocumulus• “Sonic boom cloud”

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• Relevant Textbook readings‒ Clouds• Classification of Clouds ‒ pp 122-123• Cloud Identification ‒ pp 123-128• Some Unusual Clouds ‒ pp 128-130

‒ Cloud Development (Ch 6)• (formation of lenticular clouds) ‒ p 157• Changing Cloud Forms ‒ pp 158-160

‒ Eddies and “Air Pockets” (Ch 9) ‒ p 229• (for info about billow cloud formation)

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• Relevant Web Content‒ Including clouds in a station model plot• How to read ‘surface’ weather maps

‒ http://www.srh.weather.gov/srh/jetstream/synoptic/wxmaps.htm• Cloud Symbols

‒ http://www.srh.weather.gov/srh/jetstream/synoptic/sfc_plot_symbols.htm#c

‒ Cloud Classification and Identification resources• List of cloud types from Wikipedia

‒ http://en.wikipedia.org/wiki/Cloud_types• Could not find any good online guides ….

• Great Book Resource‒ The Cloudspotter’s Guide: The Science, History and Culture of Clouds (2007)• By Gavin Pretor-Pinney 51

• No extra textbook reading …

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