AVIATION ROUTING WEATHER REPORT (METAR)
 |
Wind Group
(dddff(f)Gfmfm(fm)Kt
_dndndnVdxdxdx) |
Index
Definitions, Criteria
Wind Direction.
- The direction, in tens of degrees, from which the wind is
blowing with reference to true north.
- The wind direction shall be determined
by averaging the direction over a 2-minute period.
- When the wind direction
sensor(s) is out of service, at designated stations, the direction may be
estimated by observing the wind cone or tee, movement of twigs, leaves, smoke,
etc., or by facing into the wind in an unsheltered area.
Variable Wind Direction.
- The wind direction may be considered variable if,
during the 2-minute evaluation period, the wind speed is 6 knots or less.
- Also, the wind direction shall be considered variable if, during the 2-minute
evaluation period, it varies by 60 degrees or more when the average wind speed
is greater than 6 knots.
Wind Speed.
- The rate, in knots, at which the wind passes a given point.
- The wind speed shall be determined by averaging the speed over a 2-minute
period.
- At designated stations, Table A-1 shall be used to
estimate wind speeds
when instruments are out of service or the wind speed is below the starting
speed of the anemometer in use.
- Note: WMO standards indicate the wind speed will be
determined from the average over the 10 minutes preceding the observation and
reported in meters per second.
Wind Gust.
- The wind speed data for the most recent 10 minutes shall be
examined to evaluate the occurrence of gusts.
- Gusts are indicated by rapid fluctuations in wind speed with a variation
of 10 knots or more between peaks and lulls.
- The speed of a gust shall be the maximum instantaneous wind speed.
- Note: WMO standard defines a gust as the maximum wind speed exceeding the
"mean speed" by 5 m/s (10 knots) during the 10-minute interval.
Peak Wind Speed.
- The maximum instantaneous wind speed measured.
- Peak wind data shall be determined with wind speed recorders.
- The peak wind speed shall be the maximum instantaneous speed measured
since the last routine METAR.
Wind Shifts.
- Wind data shall be examined to determine the occurrence of a wind
shift.
- A wind shift is indicated by a change in wind direction of 45 degrees
or more in less than 15 minutes with sustained winds of 10 knots or more
throughout the wind shift.
Calm Winds.
- When no motion of air is detected, the wind shall be reported as calm.
Table A-1 Estimating Wind Speed
| Table A-1 Estimating Wind Speed |
| Knots |
Specifications |
Knots |
Specifications |
| <1 |
Calm: smoke rises vertically. |
22-27 |
Large branches in motion; whistling heard in
overhead wires; umbrellas used with difficulty |
| 1-3 |
Direction of wind shown by smoke drift not by
wind vanes. |
28-33 |
Whole trees in motion; inconvenience felt
walking against wind. |
| 4-6 |
Wind felt on face; leaves rustle; vanes moved
by wind. |
34-40 |
Breaks twigs off trees; impedes progress. |
| 7-10 |
Leaves and small twigs in constant motion; wind
extends light flag. |
41-47 |
Slight structural damage occurs.
|
| 11-16 |
Raises dust, loose paper; small branches moved. |
48-55 |
Trees uprooted; considerable damage occurs.
|
| 17-21 |
Small trees in leaf begin to sway; crested
wavelets form on inland waters. |
56-71 |
Widespread damage. |
Wind observing and reporting standards are sumarized in Table A-2.
| Table A-2 Summary of Wind Observing
and Reporting Standards |
| Parameter |
Observing and Reporting Standard |
| Wind Direction | 2-minute
average in 10 degree increments with respect to true north is reported. |
| Wind Speed | 2-minute average
speed in knots is reported. |
| Wind Gust | The maximum
instantaneous speed in knows in the past 10 minutes is reported. |
| Peak Gust | The maximum
instantaneous speed in knots (since the last scheduled report) shall be
reported whenever the speed is greater than 25 knots. |
| Wind Shifts | Wind shift and
the time the shift occurred is reported. |
Coding and Interpreting the
Coded Wind Groups
| ddd |
Wind Direction |
The wind direction
ddd, shall be coded in tens of
degrees using three figures. Directions less than 100 degrees shall be preceded
with a "0". For example, a wind direction of 90o is coded as "090".
|
| ff(f) |
Wind Speed |
The wind speed, ff(f), shall be
coded in two or three
digits immediately following the wind direction. The wind speed shall be
coded, in whole knots, (for US stations) using the units and tens digits
and, if required, the hundreds digit. Speeds of less than 10 knots shall be
coded using a leading zero. The wind group shall always end with KT (for US
stations) to indicate that wind speeds are reported in knots. For example, a
wind speed of 8 knots shall be coded "08KT"; a wind speed of 112 knots shall
be coded "112KT". International stations may use meters per second (MPS) or
kilometers per hour (KMH) and code the wind speed accordingly. |
| Gfmfm
(fm) | Gust |
Wind gusts shall be coded in the format,
Gfmfm(fm). The
wind gust shall be coded in two or three digits immediately following the wind
speed. The wind gust shall be coded, 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 would be coded "27020G35KT". |
| VRB |
Variable Wind
Direction
(Speed
6 knots
or less) |
Variable wind direction with wind speed
6 knots or less may be
coded as VRB in place of the ddd. For example, if the wind is
variable at three knots, it would be coded VRB03KT. |
| dndndn
Vdxdxdx |
Variable Wind
Direction
(Speed
greater
than 6 knots) |
Variable wind direction with wind speed
greater than 6 knots shall be coded in the
format, dndndnVdx
dxdx. The variable wind direction group shall
immediately follow the wind group. The directional variability shall be coded
in a clockwise direction. For example, if the wind is variable from
180o to 240o at 10 knots, it would be coded
"21010KT 180V240". |
| 00000KT |
Calm Wind |
Calm Wind shall be coded as "00000KT".
|
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