I'd been looking at forecasts for a while via AeroWeather and was familiar with the kind of information passed in TAFs and METARS but it was very useful to go though what I should actually get from them. I'm going to include a write up of what Tony said here for my own learning purposes.
METAR - Met Actual Report
Weather report from the Met office reporting current conditions.
The current report for Farnborough (the local service for Blackbushe) is as follows:-
EGLF 111250Z 21016KT 180V250 9999 SCT025 19/13 Q1005
EGLF - The ICAO airport code for the station.
111250Z - Date and Time. 11th, 12:50, ZULU time (GMT)
21016KT - Wind and direction. Bearing 210 16 knots. May include G for gusts and a speed.
180V250 - Wind direction variable between 180 and 250.
9999 - Visibility. 9999m or 10km. This is as good as they measure.
SCT025 - Scattered cloud at 2500ft. Just add two zeros as Tony said to Nicholas Lyndhurst. Sometimes two cloud entries when there are layers.
19/13 - Temperature and Dew Point. Tony's tip: difference x400 for visible moisture. Today 2400ft.
Q1005 - Qnh is 1005.
Other weather types that appear:-
VCXX - Vicinity XX
RA - Rain
SH - Showers
SHRA - Showers and rain, can include be + or -
DZ - Drizzle
RADZ - Rain and drizzle
MI - Mist
BR - Fog (Brume)
SN - Snow
GR - Hail (Tony says they say Granite Rain in the US - Grêle)
RERA - Recent rain
FU - Smoke (Fumée)
CB - Cumulo Nimbus
CU - Cumulus
TCU - Towering Cumulus
NSW - No significant weather
This guy has a nice article on the subject.
Cloud types are measured in 1/8ths of the sky so:-
FEW - Few clouds 1/8 to 2/8
SCT - Scattered clouds 3/8 to 4/8
BKN - Broken clouds 5/8 to 7/8
OVC - Overcast 8/8
TAF - Terminal Aerodrome Forecast
This is a weather forecast and has a stated valid time.
EGLF 111101Z 1112/1120 21016KT 9999 SCT020 TEMPO 1112/1120 20018G28KT
Station, date & time, wind, visibility, cloud are the same at the METAR
1112/1120 - valid time. In this case 11th 12:00 to 20:00.
TEMPO - Temporary condition which is no more than half of the forecast time
BECMG - Becoming, condition will change to.
PROB30 - Might happen
PROB40 - Probably happen.
Wind Check
How we calculate the cross wind component.
This is very important and based on the aircraft type we're flying. The ratings for familiar aircraft are:-
PA28 17-20 kts
C152 12 kts
We use the Clock Code to get the cross wind amount. Using runway 25 i.e. bearing of 250±10°
Wind 220 @ 40 kts. 30° difference. 30 is half clock face, so cross wind is half ∴ 20 kts.
Wind 210 @ 30 kts. 40° difference. 40 is 2/3 clock face, so 2/3 cross wind ∴ 20 kts.
Approach speed
If the wind is gusting we add 1/2 the difference in wind to the approach speed.
Thus 220 20 G30. Difference 10 means our approach speed needs 5 extra knots.
This is important on shorter runways. A PA28 has Vapp of 70kts and Vatt 65kts. 1 knot difference is about 100ft stopping space on the runway.
