Aviation Meteorology Flashcards
TEMPO
Periods of not greater than 1 hr each.
Overall period not expected to exceed 50% of the TEMPO window.
Surface wind
Mag or True?
Mean period
Max possible from METAR?
Friction effects up to what height
True (ATC will give it to you in Mag)
mean over 10 mins prior to the observation. Also compare max speed to average over rolling 2 min window and report if exceeds by 10 kts.
ATIS wind is mean of last 2 mins. Gust reported if > 10 above any 2 min mean over the past 10 mins.
Only need to report gusts if >10kts above mean!
280/25 could see gusts up to 34kts without a change in METAR.
Measured 30ft from ground
Frictional effects negligible 2-3000ft become Gradient Wind
Stronger wind = greater Coriolis effect, more parallel to isobars.
High pressure system potential weather effects
Anti-Cyclones, CW winds in Northern Hemisphere
Greater inflow of air in upper atmosphere than outflow at surface
Subsidence of air = lowering relative humidity, warming up = stability
1) Stable atmosphere, sometimes inversion and haze layers, poor visibility.
2) Inversions and stability, coupled with stronger winds can lead to MTW
3) Generally longer lived, less intense than Low Pressure systems.
Low Pressure systems
Cyclonic. Depression. ACW winds in Northern Hemisphere
Faster outflow at altitude vs surface.
Rising air which cools and condenses, saturates, lower LR can result in instability.
Unstable, Poor weather, convective clouds
Stronger, shorter-lived than Highs.
Troughs of low pressure
Line of convergence at surface, pushing air up.
Long line of convective cloud, embedded Cbs.
ISA
15C
-1.98 C/1000ft
-56.5C @ 36,090ft
1.225kg/m3
Dry Adiabatic Lapse Rate
Saturated ALR
-3C per 1000ft
-1.5C per 1000ft
Celsius to Fahrenheit
F = (9/5)C + 32
UK works 9-5 relative to US long hours… extra 32 (3+2 = 5)
C = (5/9)(F-32)
Night weather effects
Less mixing of atmosphere as minimal convection
potential inversions
stronger wind gradient / wind shear
greater difference in surface vs winds aloft (veered and stronger)
Into moon vis better (into sun vis worse)
Fog
Mist
Fog <1km vis, Mist >=1km or 5/8sm
Light surface winds 5-7kts (if no wind, then only a very thin cold layer at surface = frost/shallow fog/dew)
need light wind to suspend condensation nuclei for water particles to form fog
Cloudless night = cold surface
high relative humidity
Frontal fog: 100s of nm ahead of warm front, rain falls and increases RH at surface.
Prevailing vis
Vis experienced at over 50% of the horizon.
Military: if vis in a certain direction falls into a lower Colour State, this will be reported
Civil: lowest vis will only be reported if <1500m or <50% of the prevailing vis.
0000 means less than 50m
Icing types
Supercooled droplets
Cloud associated
Supercooled Water. Can exist down to -40C. Lower temp = smaller droplets = lower hazard. Freeze when the surface tension is disrupted?
Cb, Cu, NS. Large water droplets, convective nature can support heavier droplets. Convection = mixing = wider icing band
Stratus. smaller droplets.
Cirrus. Ice crystals, not liquid water so no impact.
Clear. 0 to -20C, large droplets (Cb, Cu, NS), portion freezes, releases Latent heat (warms rest of droplet), flows over surfaces then continues to freeze.
Rime. 0 to -40C, small supercooled droplets (layer cloud, Cb, Cu, NS) freeze instantly on contact, opaque, brittle.
Hoar Frost. water vapour sublimates to ice. Air <0C being cooled below its saturation point.
Freezing rain. ahead of a warm front/inversion rain falling through colder layer onto a cold airframe (eg long time at ALT, then on approach). Rapid build up. Vacate rain immediately, use all de-ice kit available.
0 to -20C; super-cooled liquid, severe icing,
-20 to -40C; some super-cooled droplets, smaller, moderate icing
METAR issued when?
55-59 past hour
SPECI is an unscheduled observation if weather change meets criteria
TAF validity
Up to 30hrs but tells you
FM
BCM
TEMPO
FM- rapid change
BCM - gradual usually 2 hrs or more
TEMPO- periods of 1 hr or less, and less than half the specified period
