Visibility Flashcards
What is fog
<999m
What is mist
1000> 5000 m
Relative humidity of over 95%
What is haze
Solid particles
0-5000m
What is radiation fog
When saturated air is cooled and condensed over a cold surface
What wind is required for radiation fog
2-8 knots
What height is radiation fog
Ho to 500 foot = isothermal layer
Can get an inversion ontop it layer of fog
How high is shallow fog
Up to 6ft off ground
What is valley fog
Basically the same as radiation for but in a valley
Once dispersed what clouds can valley / radiation fog rise to form
St/ Sc
What is orographic fog
Cloud formed ontop of hill
Where air cooled by adiabatic cooling
What is frontal fog
Where rain falls over wet ground
Cold air = condenses into fog
Moved with front
Forms ahead of warm front
Advection fog
Warm stable moist air moving over cold surface
Warm air cools
When cooled to due point = advection fog
What wind is needed for advection fog
10-15 knots
What is steam fog / evaporation fog / arctic sea smoke
Warm surface (sea or water)
Evaporation
Very cold air moves over
Air condenses
Usually in polar regions
What is ice fog
Temp -35°c / -40°c
Ice crystals suspended in air
Light wind to keep them there
What is freezing fog
SCWD
Rime ice
What is the visibility in High level cloud
1000 m +
What is the visibility in mid level cloud
20-1000m
What is the visibility in low level cloud
10-30 m
What precipitation has the worst visibility
Heavy snow
What precipitation had the best vis
Mod rain
what is the visibility in mod rain
3-10 km
What is the visibility in heavy rain
<1000m
What is the visibility in moderate snow
1000m
What is the visibility in drizzle
<500m
What is the visibility in heavy snow
<50m
Whay winds are required for dust or sand storms
15-30 knots
How high can dust or sand storms be
3000 ft
Can be 15,000 ft
What is the visibility in a heavy dust storm
<200m sky obscured
What is the visibility in moderate dust storm
200-600m Sky not obscured
When reporting vis should you quote an area of less vis
When it is more that 50% less than than the rest of the vis
Or less than 1500m
What is visibility or 1-5000m reported in
Metres
What increments is vis <800m reported in
50 m increments
What increments is vis 800-5km reported in
100m increments
What increments is vis 5km - 1 km reported in
1km increments
How high is a transmissometer
7.5fert above the ground
What will a rvr measure between distance wise
50 > 1500 m
What is the placement of the RVR in proximity to the runway
Not more that 120m to the side of the centre line
300m along from the threshold
What will the RVR read if the vis is less than 50m
M0050
What will the RVR read if vis is more than 1500m
P1500
What is the time range of reporting to get a RVR
10 mins before METAR then averaged
What is the time range for a ATC instant RVR report
2 mins
What distance must multiple RVR distances be quoted
When vis is less than 800m AND less than vis at threshold
Or if less than 400m
What increments is the RVR reported in when vis is below 400m
25m increments
What symbol is used when vertical vis is so bad you can’t give a vertical visibility
VV ///
What is the definition of meteorological visibility
The greatest distance at which a black object near the ground can be recognised when observed against a bright background
Or
The greatest distance at which a light of 1000 candles fam been seen and identified against an unlit background
How many points along a runway is RVR measured
3 points
How do you measure surface wind
Anemometer
