Precipitation

Question 1

6 key threats of precipitation?

Answer 1

1. Airframe icing
2. Engine flame out
3. Structural damage
4. Reduced visibility
5. Instrument impairment (blocked sensors)
6. Contaminated runway

Question 2

What are the 2 precipitation processes?

Answer 2

• Ice crystal process (Bergeron-Findeisen)

- Coalescence Process

Question 3

What happens in the ice crystal process?

Answer 3

• Ice crystals form at the expense of liquid droplets
• Clouds colder than 0 degrees
• Water vapour sublimates onto ice crystals
• Supercooled water droplets will also freeze on collision with ice crystals

Question 4

What is the coalescence theory?

Answer 4

• Clouds warmer than 0 degrees

- Tiny droplets 0.02mm diameter ascend and grow by collision with other cloud droplets

Question 5

What is the definition of hydrometeor?

Answer 5

An atmospheric phenomenon or entity involving water or water vapour, such as a cloud or rain

Question 6

What are the 5 types of hydrometeors?

Answer 6

1. Suspended particles
2. Falling particles (precipitation)
3. Particles raised by the wind from the earths surface
4. Deposits of particles
5. Spouts

Question 7

What is drizzle (DZ)?

Answer 7

Drops less than 0.5mm in diameter, falls from stratus cloud, usually low, sometimes touching the ground (fog)

Question 8

What is rain (RA)?

Answer 8

Precipitation of drops of water that falls from a cloud. Density and size varies with the intensity and nature of the precipitation

Question 9

What is freezing rain (FZRA)?

Answer 9

Rain or drizzle where the temperature drops below 0 degrees. Supercooled rain may freeze on impact with the ground or an in-flight aircraft

Question 10

What is snow (SN)?

Answer 10

Precipitation of ice crystals, singularly o stuck together. Temperatures warmer than -5 degrees where the crystals generally stick together

Question 11

What are snow grains (SG)?

Answer 11

Frozen drizzle. Very small opaque white particles of ice, diameter less than 1mm. Fall mostly from stratus or fog, never in the form of a shower

Question 12

What are snow pellets?

Answer 12

Frozen rain from low level. White and opaque ice particles, conical or rounded, diameter of 5mm. Fall from Cu or Cb

Question 13

What is hail (GR)?

Answer 13

Particles of ice. Can be transparent or opaque, spherical, conical or irregular, diameter between 5-50mm. Falls from Cb in showers

Question 14

What is small hail (GS)?

Answer 14

Precipitation of translucent ice particles, spherical and conical around 5mm in diameter. Halfway between snow pellet and hail, comes in showers from a Cb

Question 15

What are ice pellets (PL)?

Answer 15

Frozen rain from high level. Transparent ice particles usually spherical or irregular with a diameter less than 5mm. Fall from As or Ns

Question 16

What is ice crystals (IC)/diamond dust?

Answer 16

Falls from a clear sky in very small ice crystals, often appear to be suspended in the air. Typically found in rapidly cooling air masses less than -10 degrees

Question 17

What are Virga?

Answer 17

Precipitation that evaporates before it hits the ground

Question 18

What are the 2 characters of precipitation?

Answer 18

1. Intermittent

2. Continuous

Question 19

Visibility in moderate rain

Answer 19

3-10km

Question 20

Visibility in heavy rain

Answer 20

Less than 1km

Question 21

Visibility in drizzle

Answer 21

Less than 500m

Question 22

Visibility in moderate snow

Answer 22

Less than 1km

Question 23

Visibility in heavy snow

Answer 23

Less than 50m

Question 24

Effect of blowing snow

Answer 24

Can greatly reduce visibility