Clouds, Fog & Precipitation: DGCA Aviation Meteorology Questions and Answers

Cloud types by level?

Three levels (temperate regions):

• High (above 16 500 ft): Ci, Cc, Cs
• Medium (6500–23 000 ft): Ac, As, Ns
• Low (below 6500 ft): St, Sc, Cu, Cb bases

How is cloud amount reported?

In oktas (eighths of the sky):

• FEW 1–2 oktas
• SCT 3–4 oktas
• BKN 5–7 oktas
• OVC 8 oktas
• Ceiling is the lowest layer of BKN or OVC

Types of fog and how they form?

Fog is visibility below 1000 m.

• Radiation fog: clear, calm night, moist air, ground cools
• Advection fog: warm moist air over a cold surface, wind 5–15 kt
• Steam fog: cold air over warmer water
• Upslope fog: moist air forced up a slope
• Frontal fog: rain falls into cold air

Tip: Mist is 1000 to 5000 m; haze is dry particles.

Precipitation: which cloud gives what?

Match cloud to precipitation:

• Drizzle: St
• Continuous rain: Ns, As
• Showers, hail: Cu, Cb
• Snow: Ns and Cb in cold air
• Freezing rain: rain falling through a sub-zero layer (severe icing)

Five ways clouds form?

Convection, orographic lift, frontal lift, turbulent mixing and radiative cooling (fog).

Tip: Each lifts or cools air until it reaches its dew point.

Name the cloud types by height.

High (above 20 000 ft): Ci, Cc, Cs. Medium (7 000–20 000): Ac, As, (Ns). Low (below 7 000): St, Sc, Cu, Cb (Cu and Cb extend vertically).

• Stratiform: stable air, drizzle or light rain
• Cumuliform: unstable air, showers
• Cb: the most dangerous: turbulence, icing, hail, lightning

What types of fog are there?

Radiation (clear, calm night), advection (warm moist air over a cold surface), steaming (cold air over warm water), upslope and frontal.

• Fog: visibility < 1 000 m
• Mist: visibility 1 000–5 000 m
• Radiation fog forms with light wind (2–8 kt) and burns off by day
• Advection fog needs wind (5–15 kt) and can persist