Chapter 24
Observations
The pilot reports the weather conditions encountered as follows: flight visibility, when reported, is entered first in the /WX field. It is coded FV followed by a two-digit visibility value rounded down, if necessary, to the nearest whole statute mile and appended with SM (e.g., FV03SM). If visibility is reported as unrestricted, FV99SM is entered.
Flight weather types are entered using one or more of the surface weather reporting phenomena contained in Table 24-3.
Example:
/WX FV01SM +DS000-TOP083/SKC /RM DURC Flight visibility 1 SM, base heavy dust storm layer at the surface, top 8,300 ft MSL, clear above, remarks, during climb.
When more than one form of precipitation is combined in the report, the dominant type is reported first.
Examples:
/WX FV00SM +TSRAGR Flight visibility 0 SM, thunderstorm, heavy rain, hail.
/WX FV02SM BRHZ000-TOP083 Flight visibility 2 SM, base of a haze and mist layer at the surface, top 8,300 ft MSL.
If a funnel cloud is reported, it is coded FC following the /WX group and is spelled out as FUNNEL CLOUD after the /RM group. If a tornado or waterspout is reported, it is coded +FC following the /WX group, and TORNADO or WATERSPOUT is spelled out after the /RM group. If a dust/sand whirl (dust devil) is reported, it is coded FC following the /WX group, and DUST/SAND WHIRL (DUST DEVIL) is spelled out after the /RM group.
Examples:
/WX FC /RM FUNNEL CLOUD Funnel cloud, remarks, funnel cloud.
/WX +FC /RM TORNADO Tornado, remarks, tornado.
When more than one type of weather is reported, they are reported in the following order:
- TORNADO, WATERSPOUT, FUNNEL CLOUD, or DUST/SAND WHIRL (DUST DEVIL).
- Thunderstorm with or without associated precipitation.
- Weather phenomena in order of decreasing predominance.
- No more than three groups are used in a single PIREP.
- Weather layers are entered with the base and/or top of the layer when reported. The same format as in the sky condition (/SK) group is used.
Example:
/WX FU002-TOP030 Base of a smoke layer, 200 ft MSL, top 3,000 ft MSL.
24.5.1.8 Air Temperature (/TA)
Outside air temperature (/TA) is reported using two digits in degrees Celsius. Negative temperatures are prefixed with an M (e.g., /TA 08 or /TA M08).
24.5.1.9 Wind Direction and Speed (/WV)
Wind direction and speed are encoded using three digits to indicate wind direction, relative to magnetic north, and two or three digits to indicate reported wind speed. When the reported speed is less than 10 kt, a leading 0 is used. The wind group will always have KT appended to represent the units in knots.