Estimating wind without instruments
No wind-measuring equipment or ground indicator: read wind from what moving air disturbs (smoke, dust, flags, wind lines on water) (TC AIM MET 2.6).
Beaufort Wind Scale grades observed effects into a numbered force. Land effects are the pilot reference:
| Force | Term | Speed (kt) | Land effect |
|---|---|---|---|
| 0 | Calm | less than 1 | smoke rises vertically |
| 1 | Light Air | 1-3 | direction of wind shown by smoke |
| 2 | Light Breeze | 4-6 | wind felt on face, leaves rustle, ordinary vane moved |
| 3 | Gentle Breeze | 7-10 | leaves and small twigs in constant motion, extends a light flag |
| 4 | Moderate Breeze | 11-16 | raises dust and loose paper, moves small branches |
| 5 | Fresh Breeze | 17-21 | small trees in leaf sway, crested wavelets on inland water |
| 6 | Strong Breeze | 22-27 | large branches move, telephone wires whistle, umbrellas hard to use |
| 7 | Near Gale | 28-33 | whole trees in motion, inconvenience felt walking against the wind |
| 8 | Gale | 34-40 | breaks twigs off trees, generally impedes progress |
| 9 | Strong Gale | 41-47 | slight structural damage to roofing shingles, TV antennae |
| 10 | Storm | 48-55 | seldom felt inland, trees uprooted, considerable structural damage |
| 11 | Violent Storm | 56-63 | very rare, widespread damage |
| 12 | Hurricane | above 63 | air filled with foam and spray, visibility seriously affected |
Direction:
- Face the wind, standing in an open area clear of obstructions.
- Report only to nearest eight compass points (N, NE, E, etc.), never a precise heading.
Other cues:
- Low cloud drift hints at surface wind. Near-surface wind shear can make it a poor match.
- No surface indication: base estimate on wind at point of departure and forecast for destination (TP 1102).
- Label relayed wind estimate, not measured.
Trap: estimate to nearest degree or sixteen points overstates accuracy; TC AIM caps it at eight points.
References
- TC AIM MET 2.6