Page 36 - AFMAN 15-111, 12 MAR 2019

36 AFMAN15-111 12 MARCH 2019

Chapter 7

WIND

7.1. Introduction. This chapter describes the observing and reporting standards for wind data.
Wind is measured in terms of velocity, a vector that includes direction and speed. To the maximum
extent possible, wind is measured in an unobstructed area to minimize inconsistencies caused by
local obstructions that may result in an unrepresentative report of the general wind patterns.
7.2. Wind Group (dddff(f)Gfmfm(fm)KT_dndndnVdxdxdx).

7.2.1. Direction. The true direction (ddd) the wind is blowing from is encoded in tens of
degrees using three figures. Directions less than 100 degrees are preceded with a "0." For
example, a wind direction of 90 is encoded "090."

7.2.2. Speed. The wind speed, ff(f), is entered as a two- or three-digit group immediately
following the wind direction. The speed is encoded in whole knots using the tens and units
digits. The hundreds digit is only used when the wind speed exceeds 100 knots and is never
reported as a leading zero. Speeds of less than 10 knots are encoded using a leading zero in the
tens position. The group always ends with KT to indicate the wind speeds are reported in knots.
For example, a wind speed of 8 knots is encoded 08KT. A wind speed of 112 knots is encoded
112KT.

7.2.3. Gust. Wind gusts are encoded in the format, Gfmfm(fm). The wind gust is encoded in two
or three digits immediately following the wind speed. The wind gust is encoded in whole knots
using the units and tens digits and, if required, the hundreds digit. For example, a wind from
due west at 20 knots with gusts to 35 knots is encoded 27020G35KT.
7.2.4. Variable Wind Direction (speeds 6 knots or less). Variable wind direction with wind
speed 6 knots or less may be encoded as VRB in place of the ddd. For example, if the wind is
variable at three knots, it could be encoded VRB03KT.
7.2.5. Variable Wind Direction (speeds greater than 6 knots). Wind direction varying 60
degrees or more with wind speed greater than 6 knots is encoded in the format, dndndnVdxdxdx.
The variable wind direction group immediately follows the wind group. The directional
variability is encoded in a clockwise direction. For example, if the wind is variable from 180
to 240 at 10 knots, is encoded 21010KT 180V240.

7.2.6. Calm Wind. Calm wind is encoded as 00000KT.
7.3. Wind Algorithms. The wind algorithm uses 5-second average wind directions and speeds
to compute and report the 2-minute average in the observation. The 5-second speed is also used as
the instantaneous wind to determine gusts, squalls and peak wind data. The 2-minute direction is
used to determine wind shifts and the range of variability.
7.4. Standards and Reporting. FBWOS sensors determine the wind direction, speed, gusts,
wind shifts and peak wind at all automated observing locations. See Table 7.1 for a quick reference
of wind element reporting characteristics.