Max wind
ICAO Annex 3, Appendix 3
4.1.2.2 Recommendation.— The mean values of, and
significant variations in, the surface wind direction and speed
for each sensor should be derived and displayed by automated
equipment.
4.1.3 Averaging
4.1.3.1 The averaging period for surface wind obser-
vations shall be:
a) 2 minutes for local routine and special reports and for
wind displays in air traffic services units; and
b) 10 minutes for METAR and SPECI, except that when
the 10-minute period includes a marked discontinuity in
the wind direction and/or speed, only data occurring
since the discontinuity shall be used for obtaining mean
values, hence the time interval in these circumstances
should be correspondingly reduced.
4.1.4 Reporting
4.1.4.1 In local routine and special reports and in
METAR and SPECI, the surface wind direction and speed
shall be reported in steps of 10 degrees true and 1 kilometre
per hour (or 1 knot), respectively. Any observed value which
does not fit the reporting scale in use shall be rounded to the
nearest step in the scale.
c) variations from the mean wind speed (gusts) during the
past 10 minutes shall be reported when the maximum
wind speed exceeds the mean speed by 20 km/h (10 kt)
or more;
In ATTACHMENT D it says more precisely:
2min average wind for Local routine and special report and if wind exceeding the mean speed (2min) by 10kt as max value.
10min average wind for METAR/SPECI and if wind exceeding the mean speed (10min) by 10kt as max value.