Page 38 - AFMAN 15-111, 12 MAR 2019

38 AFMAN15-111 12 MARCH 2019

7.5. Manual Observing Methods.

7.5.1. Predominant wind direction, speed, gusts, and shifts are determined by the primary
active wind sensor; peak wind data is determined by all available runway sensors. Data
obtained from alternate equipment may be used as a guide for determining winds when the
primary sensor is considered unrepresentative or inoperative. Note: Winds will be reported as
estimated when obtained from any source other than the properly sited wind sensor for the
active runway (T-2). See Attachment 3 for remark format.

7.5.2. To determine wind direction manually using a compass (or digital measuring device),
face into the wind in an unobstructed area and take a 2-minute average reading of the wind
direction; convert this magnetic direction to true direction where applicable. While
determining the predominant direction, take note of the limits of variability for reporting when
applicable. Note: Do not use the movement of clouds, regardless of how low they are, in
determining the surface wind direction.
7.5.3. To determine wind speed manually, using an approved anemometer face into the wind
in an unobstructed area with the device held at eye-level and take a 2-minute average reading
of the wind speed. Use the same method over a 10-minute period to determine gusts when
applicable. If an instrument is not available, use the Beaufort scale (Table 7.2) to determine
the wind speed.

Table 7.2. Beaufort Scale of Winds.

Wind Equivalent -- Beaufort Scale
Beaufort # MPH KTS Terminology Description
0 <1 <1 Calm Calm. Smoke rises vertically.
1 1-3 1-3 Light Air Wind motion visible in smoke.
2 4-7 4-6 Light Breeze Wind felt on exposed skin. Leaves rustle.
3 8-12 7-10 Gentle Breeze Leaves and smaller twigs in constant motion.
Moderate Dust and loose paper are raised. Small branches
4 13-18 11-16
Breeze begin to move.
5 19-24 17-21 Fresh Breeze Smaller trees sway.
Large branches in motion. Whistling heard in
6 25-31 22-27 Strong Breeze
overhead wires. Umbrella use becomes difficult.
Whole trees in motion. Some difficulty when
7 32-38 28-33 Near Gale
walking into the wind.
8 39-46 34-40 Gale Twigs broken from trees. Cars veer on road.
9 47-54 41-47 Severe Gale Light structure damage.
10 55-63 48-55 Storm Trees uprooted. Considerable structural damage.
11 64-72 56-63 Violent Storm Widespread structural damage.
12 73-82 64-71 Hurricane Considerable and widespread damage to structures.