The character of the wind refers to the increase and decrease or variability of speed in
gusts.
Gust
A gust is a change in speed of 10 knots or more between peaks and lulls. The speed of
the gust is the maximum instantaneous wind speed recorded during the most recent 10
minutes of the actual time of the METAR or SPECI. Gusts are encoded by suffixing the
letter G to the average speed followed by the peak speed in the gusts.
For example, if the wind is from 070, the average being 20 knots with gusts of 35
knots, this wind group would appear as "07020G35KT."
Visibility Group
Visibility is an extremely important factor in the decisions you will be making that involve
air traffic control. For this reason, your visibility reports must be timely and accurate.
Visibility is the greatest distance at which selected objects can be seen and identified.
Visibility is reported in statute miles (nautical miles onboard ships) and fractions thereof
up to 3 miles, the nearest whole mile from 3 to 15 miles, and the nearest 5 miles beyond
15 miles. Because of horizon limitations, 7 miles is considered unrestricted. Few
stations can see beyond 7 miles.
When you are assigned to a control tower, you are required to make tower prevailing
and sector prevailing visibility observations when the visibility is less than 4 miles.
NAVMETOCCOMINST 1500.3G provides procedures to certify control tower personnel
to take visibility observations. From the control tower, you are able to observe rapidly
changing conditions and inform weather personnel and pilots of deteriorating conditions
that may affect the safe operation of aircraft.
Prevailing visibility is reported in the hourly aviation weather report or METAR.
Prevailing visibility is the greatest distance that you can see throughout at least half of
the horizon circle. The half of the horizon circle need not necessarily be continuous.
Figure 1-12 indicates how to obtain prevailing visibility from the horizon circle.
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