Based on the following ICAO Annex 3 criteria for the use of the abbreviation VRB (not FAA, which is different and evident):
when the total variation is 60° or more and less than 180° and the wind speed is 3 kt or more, such directional variations shall be reported as the two extreme directions between which the surface wind has varied
when the total variation is 60° or more and less than 180° and the wind speed is less than 3 kt, the wind direction shall be reported as variable with no mean wind direction; or
when the total variation is 180° or more, the wind direction shall be reported as variable with no mean wind direction"
I bring up the following QUESTIONS
- Based on these criteria, is there a way to identify if a variable 2KT wind is varying less or more than 180° when the indication is just VRB02KT?
If it were varying less than 180° but at least 60° or more, would it be possible to measure its mean direction and direction range despite its low intensity of just 2KT? E.g. 15002KT 110V200.
If not, it brings me back to my first question, what is the actual variation of a VRB02KT, less or more than 180°? Could I just answer impossible to specifically tell, but it is surely 60° or higher, otherwise the mean direction would be possible to measured, even at only 2KT. E.g. 15002KT
- If the wind intensity following a VRB indication is 3KT or more, can I assume it is varying more than 180°? Since this excessive variation in direction (not the relatively low intensity of 3KT) is the reason why the station can't measure the mean direction precisely.
E.g. VRB03KT would mean varying by more than 180° (not 60° or more, and less than 180°) with an intensity of 3KT (which would be strong enough to provide feasible conditions for measuring the mean direction, if it wasn’t for its excessive variation in direction above 180°).