Met 5 - Clouds a n d Precipitation

What does precipitation generally indicate about cloud thickness?

It implies cloud is at least 4000 ft thick. Heavier precipitation = thicker clouds.

What type of clouds typically produce light precipitation like drizzle or light rain?

Stratiform clouds like stratus and stratocumulus.

What type of clouds typically produce heavier precipitation, including hail?

Cumuliform clouds like cumulonimbus.

What is the METAR code and water droplet size range for drizzle?

DZ; Water drops between 0.2 mm and 1.0 mm.

What is the METAR code and water droplet size range for rain?

RA; Water drops between 1.0 mm and 5.8 mm.

What is the term for the merging of smaller droplets into larger ones inside clouds?

Coalescence.

What happens to water drops larger than 5.8 mm in the air?

They break up due to pressure from the airflow.

What is the METAR code for snow and how is it defined?

SN; Precipitation in the form of ice crystals.

What is the typical temperature at which snow is associated?

Around 0°C (freezing point).

What is the METAR code for snow grains and what are they?

SG; Small ice particles, frozen equivalent of drizzle.

What is the METAR code for hail and what clouds produce it?

GR; Produced in well-developed cumulonimbus clouds.

What is the METAR code for ice pellets and which cloud type produces them?

PE; Fall from thick layered clouds like nimbostratus.

What is diamond dust (IC)?

Tiny ice crystals suspended in calm, clear Arctic air.

What is virga?

Precipitation that evaporates before reaching the ground.

What is sleet and is it universally recognized in meteorology?

Sleet varies by region; it's not used in international METARs to avoid confusion.

How is precipitation intensity shown in METARs/TAFs?

No symbol = moderate, "-" = slight, "+" = heavy.

What does the METAR "7 KM RA" indicate?

7 kilometres visibility, moderate rain.

What does "ISOL 3000 M +RA" indicate?

Isolated 3000 metres visibility, heavy rain.

What does "OCNL 5000 M RA/RADZ" indicate?

Occasionally 5000 metres visibility, moderate rain and drizzle.

What does "15 KM NIL-RA" indicate?

15 kilometres visibility, nil precipitation or slight rain.

Why does drizzle pose a risk to flight operations?

Associated with low cloud, poor visibility, and high humidity — increases carb icing risk.

How does heavy rain affect runways?

Reduces braking, especially dangerous on wet grass runways — increases takeoff and landing distance.

What does SNOCLO mean in a VOLMET report?

UK airfield closed due to snow.

What are the typical cloud levels for low, medium, and high clouds?

Low: below 6500 ft; Medium: 6500–23,000 ft; High: 16,500–45,000 ft.

What are clouds with large vertical extent that may reach through tropopause?

Cumulonimbus.

What are the defining features of stratus clouds?

Sheet-like layer, very low base, stable air, poor visibility, no turbulence.

What is stratocumulus?

Patchy layered cloud formed by mixing or lifting, white or grey, formed from cumulus collapse or inversion.

What is turbulent mixing and how does it form cloud?

Warm air mixes with cool air, reaching dew point, forming stratocumulus.

What is anticyclonic gloom?

Persistent winter cloud caused by temperature inversion under high-pressure systems.

What is a key operational risk of precipitation on a wet grass runway?

It significantly lengthens the takeoff and landing distance.