Clouds Flashcards
What decides what type of clouds form?
The stability and moisture content in the atmosphere
What are metar codes for cloud coverage?
SKC: Sky clear
FEW: Few, 1/8 - 2/8 oktas of sky covered
SCT: Scattered, 3/8 - 4/8 oktas
BKN: Broken, 5/8 to less than 8/8
OVC: Overcast, 8/8 covered
What is a ‘ceiling’?
- A cloud base you are not allowed to fly over as a VFR pilot
- A ceiling exists whenever the sky is either BKN or OVC (5/8 - 8/8)
- Ceiling is also defined by a Vertical Visibility (VV). Example: VV001 = ceiling obscured at 100 feet
How are ceilings depicted on a GFA?
With a scalloped border. In the image below:
- Ceiling begins at 8000ft ASL and the top of the clouds are at 18000ft ASL
What does ‘patchy’ on a GFA mean?
25% of the time or less
Clouds are classified into four families based on their…
Height:
- High cloud
- Middle cloud
- Low cloud
- Clouds with verticle development
Verticle development:
- Strata-form: Strata means to spread out
- Cumuli-form: cumuli means to move upwards
What are Cirrus clouds?
- Highest clouds, above 20000ft
- Whispy appearnce
- Occur in high pressure systems and fair weather
- Will point in the direction of air movement at their elevation
- Composed of ice crystals
What are the subdivisions of cirrus (high) clouds?
Cirrostratus: Sheet-like, white veil, high level clouds made of ice crystals. Tend to thicken as a warm front approaches. Sun and Moon can be seen through them, often surrounded by a halo.
Cirrocumulus: Somewhat rare. Appears as a white, pebbly sheet. Or like fish scales.
What are the three types of Middle Cloud?
- Uses the prefix Alto, which ironically means high, not middle.
- Altostratus (AS)
- Altocumulous (AC)
- Altocumulous Castellanus (ACC)
What are altostratus clouds?
- Alto = middle
- Stratus = spread out
Layered cloud with no pattern. May cover entire sky
Sometimes moon or sun can been seen through altostratus but there is no halo like with cirrostratus. More looks like it’s behind frosted glass.
Cant produce heaavy rain but light drizzle can happen.
What are altocumulus (AC) clouds?
- Middle layer cloud
- Puffy cotton ball clouds
- May be followed by thunderstorms
- Icing ususaly present in the cloud, particularly at the tops of the clouds
What are alto cumulus castellanus (ACC) clouds?
Alto - middle
Cumulous - puffy, verticle
Castllanus - …castle???
- Created from very unstable air.
- Similar to altocumulus but with pronounced turrets spiking upward that may develop into cumulonimbus
What is a stratus cloud? (ST)
- Low with a uniform layer
- Smooth air, little turbulence
- Resembles fog but doesnt touch the ground.
- Drizzle, but no rain
What is a nimbostratus cloud?
- Low, main precipitation cloud
- Continuous rain, snow, whatever
- Nimbo means precipitation
- Extensive layer, dark, with bases from 6500ft down to surface
What is stratocumulous?
- Low, spread out, lumpy layer of clouds
- Bottom has a wavy or rolled appearance
- Occasionally moderate turbulence
- Occasional convective clouds embedded within
- Only gives precip in winter or high pressure system.
What are stratus and cumulus fractus?
Stratus and cumulous clouds that get ripped apart by strong winds.
What are fair weather cumulus clouds?
- No cirrus and no alto prefix means this is a low cloud
- Floating cotton balls or popcorn
- Only last 5 to 40 minutes
- Indicated significant vertical currents at low levels without precip
- Common over land in hot summer
- Turbelence light to moderate
Clouds with verticle development
What are mamatus clouds?
- The creepy bubbly sheet cloud
- Indicate an extremely unstable atmosphere
- Thunderstorm likely to follow
What is the difference between a roll cloud and a rotor cloud?
- Rotor cloud - caused by mountain waves. These clouds actually spin around violently. Cause by gradient winds shifting from the surface to that at altitude.
- Roll Cloud - caused by up and down drafts under and to the side of a thunderstorm.
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