16 Visibility

Question 1

What are the three things which cause obscurity?

Answer 1

• Water droplets
• Ice
• Solid particles

Question 2

What are the thresholds of reporting visibility from the tower and when would multiple reports be given?

Answer 2

Thresholds are:

~ reported in 50m steps up to 800m
~ reported in 100m steps up to 5km
~ reported in 1km steps up to 10km

If visibility is below 50% or 1500m then multiple reports are given.

Question 3

Visibility in precipitation:

Answer 3

~ Moderate rain - 3 to 10km
~ Heavy rain - < 1000m
~ Moderate Snow - 1000m
~ Drizzle - < 500m
~ Heavy Snow - < 50m
~ Blowing Snow - Limited to no visbility

Question 4

Visibility in cloud levels

Answer 4

~ High cloud: 1000m+
~ Medium cloud: between 20 and 1000m
~ Low cloud: between 10 and 30m

Question 5

What are visibility ranges for fog and mist and what are they made of?

Answer 5

~ Fog: up to 999m
~ Mist: between 1000m and 5000m

~ Made from water droplets and solid particles

Question 6

What is the visibility range for Haze and what is it made of?

Answer 6

~ Up to 5000m

~ Made from solid particles only

Question 7

What is Radiation Fog and describe:

• Conditions needed
• What causes it to disipate
• How high it can sit

Answer 7

• Formed when the surface cools rapidly causing the layer of air in contact with the surface to cool as well.
• Conditions:
  
  • Clear sky
  • Light wind (2 to 8 kts)
  • Humidity
• Dissipates from insolation
• Sits up to 500 to 1000m high

Question 8

Describe Advection Fog and:

• Conditions required
• How it dissipates

Answer 8

• Caused by the horizontal movement of a warm air mass over a cold surface
• Conditions:
  
  • Moving, warm air mass
  • Cold surface
  • Humidity
• Dissipates when the air mass moves on

Question 9

Describe Evaporation Fog and:

• Aka
• Conditions required

Answer 9

• Aka Steam Fog or Arctic Sea Smoke
• Caused when a cold air mass moves over a warm sea or body of water
• Conditions:
  
  • Warm body of water
  • A moving cold air mass

Question 10

Frontal Fog

Answer 10

• Proceeds a moving warm front with rain clouds. The precipitation falls from the warm air into the cool air below which becomes saturated and creates fog.
• Conditions:
  
  • Moving warm front
  • Rain clouds and precipitation
• Fog can precede the warm front by 200nm

Question 11

Hill / Orographic Fog

Answer 11

• Caused when air is forced to rise up the side of a hill

Question 12

What are the Runway Visual Range (RVR) limits and thresholds for measurement?

Answer 12

• Measures between 50m and 1500m
• Between 50m and 400m in 25m steps
• Between 400m and 800m in 50m steps
• 800m+ in 100m steps

Question 13

What are the Runway Visual Range Codes?

Answer 13

• P: More than
• M: Less than
• U: Increasing
• D: Decreasing
• N: No change