MET CONDENSED NOTES
Cloud Abbreviations:
Few = 1 – 2 Oktas
SCT = 3 to 4 Oktas
BKN = 5 to 7 Oktas
OVC = 8 Oktas
Vertical Vis reported in:
Expressed in FT = Steps of 100ft up to 2000ft
Expressed in M = Steps of 30m up to 600m
RVR reported when the visibility decreases below 1500m
U = Increasing
D = Decreasing
N = No change
Two dashed lines = The height of the jet stream axis changes by + / - 3000ft and / or the speed varies by + / - 20 kts.
Warm High = Intensifies with increasing altitude.
Ice Water Content: A measure of how much ice is present in a certain
volume of air. Measured in g/m³, and reaches max values in the upper
levels of the core of convective systems. (Ice Volume per unit volume of
air)
Grid Forecast: Looks at latitude / longitude and vertical data (height or
pressure).
Ahead of warm front = continuous light rain
from AS, then moderate to heavy
continuous rain from NS.
At the warm front = moderate or heavy
continuous rain / snow from NS
In the warm sector = Continuous
precipitation stops, only light rain / drizzle is
observed or no rain at all.
At the cold front: Heavy rain or snow,
thunderstorms or hail.
Behind the cold front: heavy rain or snow,
then no precipitation, and then later
occasional showers from CU and CB.
When – West Australia = 5
Human – Hurricane = 6
People – Pacific = 9
Buy – Bay of Bengal = 12
Jeans – Japan = 20
RH = 100 – 5 (Temp – DP)
Advection Fog: Formed by warm, moist air moving over a cold surface.
Air mass is cooled from below often causing an inversion.
Formed day or night
Advection = Across
Requires the following to form:
o
Wind of up to 15 kts
o
Cold surface
o
Humid air
o
Temperature difference between surface and air.
Thermal Depression: (Non-Frontal Depression) occur over land in summer,
as a result of strong surface heating.
In winter they occur over sea areas in cold polar or arctic air
masses.
Weather associated:
o
CU & CB
o
Heavy showers
o
Good vis
o
Mod / Sev turbulence
After the passage of a cold front:
Wind Direction: Sudden change, before the front winds are from the west / south west. When the front has passed the winds
veer to the north west.
Pressure: Increases slowly.
Precipitation: Same as the cold front then no precipitation, later occasion showers.
World Area Forecast: Prepare and issue significant weather forecasts and upper-air forecasts in digital form, on a global basis.
Upper wind
Upper air temp and humidity
Geopotential altitude of flight levels
Flight level and temp of tropopause
Direction, speed and flight level of max wind
Cumulonimbus cloud
Icing
Turbulence
DALR: 3° per 1000ft
SALR: 1.8° per 1000ft
ELR greater than DALR = absolutely unstable
ELR less than SALR = absolutely stable
Neutral Stability = ELR is qual to the DALR
ELR Between DALR and SALR = Conditionally unstable
Isothermal Layer = Absolutely stable
Flying below the jet core = slight increase in OAT when going from polar to tropical
air
Flying at the jet core level = no OAT change
Flying above the jet core = decrease in OAT when going from polar to tropical air
Latent heat released: Gas to liquid or solid.
Latent head absorbed: Liquid or solid to gas.
Vertical Visibility: Reported only whenever the sky is obscured by fog or heavy precipitation, and the height of the cloud base cannot be
measured.
Adiabatic: No heat transfer takes place (no heat added or taken away from the parcel of air).
Dew Point:
Increasing temperature has no effect on the dew point.
Decreasing temperature has no effect as well, UNTIL the dew point temperature is reached.
Transition Altitude = Climbing
Transition Level = Descending
Relative Humidity = When temperature increases, the relative humidity decreases due to the parcel of air expanding.
The dew point remains constant during this.
Trend Forecast: A landing forecast appended to METAR / SPECI which is valid for 2 hours.
CAT: Satellite sensors are unable to detect CAT, therefore precise forecasting of such a phenomenon is very difficult.
Gridded Forecasts: Help flight crews and dispatchers to visualise flight hazards better.