Reading the wind

How to read the wind’s direction, strength and gusts from windsocks, streamers, trees, water, smoke, birds and other wings — and how thermal cycles and student limits turn that reading into “go” or “wait”.

In this lesson you will

On your first morning at the training hill, nobody unpacks a wing straight away. Your instructor stands and looks — at the windsock, the trees, the clouds, a lake in the valley — and only then makes the plan for the day, or decides to wait.

That habit is worth copying from day one. The force of the wind on your wing grows with the square of its speed: twice the wind pulls about four times as hard¹. And one manufacturer’s manual puts it bluntly: most serious accidents come from pilots misjudging the weather, not from equipment failure².

Three questions

Every time you read the wind, you answer three questions. Where is it coming from: straight up the slope, from the side or from behind? How strong is it for you today? How steady is it: a smooth breeze, or gusts and lulls? No single indicator answers all three, so you build the picture from several.

The windsock

A windsock streams downwind: its open mouth faces into the wind and its tail points the way the air is going. The stronger the wind, the higher and fuller it flies.

Standard airport socks are built to a specification, so their angle gives a rough speed³⁴:

Airport sock	Wind
Hanging down the pole	Calm or very light
About 30° below horizontal	About 6 kt (11 km/h7 mph)
About 5° below horizontal	About 10 kt (19 km/h12 mph)
Horizontal	15 kt (28 km/h17 mph) or more

A horizontal airport sock therefore means at least about 28 km/h17 mph — already above the published student limits of USHPA and APPI³. Even a sock just below horizontal, about 19 km/h12 mph, is at or above those limits⁴.

Flying-site socks are usually smaller and lighter and are not built to any standard, so they can respond quite differently³⁴. Find out how yours behaves by comparing it with a hand-held wind meter, the anemometer; many instructors prefer a meter to judging the wind on your face⁵.

Figure: Slide the wind and watch the sock lift and fill; add gusts to see it swing up. The panel shows the same wind on land and water. Angles are for a standard airport sock.

Slide the wind and watch the sock lift and fill; add gusts to see it swing up. The panel shows the same wind on land and water. Angles are for a standard airport sock.

Remember where the sock is: near the ground, where friction slows the wind. Many schools warn that the wind your wing meets a few metres up can be up to about 10 km/h6 mph stronger than what you feel on launch⁶; that is the wind gradient (its lesson explains it).

Streamers on poles, bushes or a wing’s lines show the direction moment to moment; use them alongside the sock.

Nature’s wind indicators

Trees, water and smoke are wind indicators too. The Beaufort scale links what you see to the wind speed⁷⁸:

Force	Wind	On land	On water
1	1–5 km/h1–3 mph	Smoke drifts and shows the direction	Ripples like scales
2	6–11 km/h4–7 mph	Felt on the face; leaves rustle	Small, short wavelets
3	12–19 km/h7–12 mph	Leaves and twigs always moving; flags start to move	Larger wavelets; crests begin to break
4	20–28 km/h12–17 mph	Dust and loose paper lifted; small branches move	Small waves, frequent white horses
5	29–38 km/h18–24 mph	Small trees in leaf begin to sway	Moderate waves, many white horses

The speeds are averages at the standard height of 10 m35 ft over open land, so the wind where you stand is usually weaker⁷.

Smoke shows more than direction. In windy, overcast air the plume spreads up and sideways about equally; with thermals it loops up and down; in very stable air it drifts away in a flat ribbon⁹.

Birds and other wings show the air higher up. Circling birds, wings or sailplanes often mark a thermal; moving cloud shadows show the wind at cloud base¹⁰. Wings that must point well into wind to hold their line, and barely move over the ground, are in strong wind¹¹.

Compare these overall signs — cloud drift, water, bird drift, smoke — with the indicators on launch. USHPA teaches its P2 (Novice) students to do exactly this to spot possible rotor, and to expect the wind direction to differ between launch and landing¹².

Warning Danger signs

USHPA lists these weather danger signs for P2 (Novice) pilots: high wind, blowing dust, white caps, swaying trees, smoke blown flat along the ground, and lenticular clouds¹³. Any one of them means “not today” for a student.

Safety-critical Dust devils

A dust devil is a small, violent whirlwind over strongly heated ground in light wind. Three of the 48 paragliding deaths of German pilots in 2018–2022 were caused by dust devils, one during ground handling¹⁴. If you see one, keep your wing packed or held down and stay clear.

Gusts and the gust factor

A gust is a short burst of stronger wind; the quieter spells between are lulls. In aviation weather a wind only counts as gusty when it varies by about 10 kt (19 km/h12 mph) or more between peaks and lulls. The gust factor is the difference between the steady wind and the gusts¹⁵.

That matters when you read an airport report or weather station. Airport reports give a two-minute average and add a gust figure only when that large spread occurs, so a report with no gust figure can still hide gusts nearly 19 km/h12 mph stronger than the lulls: on a 12 km/h7 mph report, peaks near 30 km/h19 mph. Reports are also minutes old; the windsock shows the wind now¹⁵.

Gusts matter more than the average because of the square law: a gust from 15 km/h9 mph to 25 km/h16 mph nearly triples the pull on your wing¹. USHPA’s limits for new pilots include a maximum peak gust and a maximum rate of rise, not just an average¹⁶: the gusts set the hardest moments.

Thermal cycles on launch

On sunny days the wind on launch comes in waves as thermals form and pass, and after a spot has released a thermal the sun needs time to reheat it for the next one¹⁷. Pilots call each wave a cycle. The pattern varies from site to site, but often the wind builds, gets gusty and may swing in direction, then fades into a lull — sometimes with no wind at all, or a light breeze from behind.

Judging the cycles is part of a standard launch assessment: APPI’s first-level students analyse the wind’s strength, direction and thermal cycle, and a school wing’s manual lists thermal cycles among the conditions to assess before launch¹⁷. Cycle lengths vary with the site and the day: watch several, and listen to the site briefing.

Figure: An illustrative trace of the wind on a thermic launch. The windows are the steady stretches, within your limit and straight up the slope — not the strongest gusts, and not the lull.

An illustrative trace of the wind on a thermic launch. The windows are the steady stretches, within your limit and straight up the slope — not the strongest gusts, and not the lull.

You are waiting for a stretch of steady wind, within your limit and straight up the slope. SafePro, the international reference, warns students against taking off in cross, down, gusty or strong winds¹⁸. Exactly when in the cycle to go is your instructor’s call.

Student wind limits

Standards differ Student wind limits on site

Common ground: Every system limits the wind students fly in, but only some publish numbers, and they measure different things. Your instructor sets your limits for the day; when a published figure and your instructor’s differ, the lower one applies.

USHPA (USA): Recommended operating limits, not law. P1: steady wind of 19 km/h12 mph, foot launching on slopes of 3:1 to 4:1 with the wind within 15° of straight up¹⁹. P2: base wind 19 km/h12 mph, peak gusts 24 km/h15 mph, gusts building no faster than 8 km/h5 mph in 5 s, foot launches only on slopes steeper than 4:1 with the wind within 25° of straight up, and no flying in thermals with peak climbs above 1 m/s200 ft/min¹⁶. The Foot Launch skill every P2 needs includes no-wind launches in 0–8 km/h0–5 mph, high-wind launches in 16–24 km/h10–15 mph, and launches with the wind at least 15° off straight up the hill in winds up to 8 km/h5 mph²⁰.
BHPA (UK): No numeric paraglider student limits are published: your school sets them in its training records, which are not public, and the numeric limits in the BHPA’s Technical Manual are for hang-gliding training²¹. The post-Club Pilot Foundation exercises use wind bands — defined-area landings in winds under 8 km/h5 mph, reverse inflations under 19 km/h12 mph and reverse launching over 19 km/h12 mph — as training conditions, not limits²².
APPI (international): APPI 1–3 (Open Sky, Adventure and APPI Pilot): a maximum of 15 km/h9 mph for the ground-handling tasks, on the flat and on 5–20° training slopes. Crosswind comes step by step: an inflation with 30° of side wind at APPI 2 and a launch with at most 45° at APPI 3. The limit rises to 25 km/h16 mph only at the later Advanced Pilot level²³.
FAI/CIVL SafePro (international reference): Words only. Stage 1 students flying without direct supervision keep to light, smooth headwinds; Stage 2 students to light to moderate smooth winds, launching roughly into wind. Both stages warn against cross, down, strong or gusty wind, and a crosswind launch of up to 45° appears only at Stage 5²⁴.

Summarised from each body’s published material, which changes over time. Check the current official documents and follow your school.

The forecast lesson covers thermals and the wind higher up.

Reading the wind, step by step

Before you unpack

Look at the big picture first — clouds, smoke, trees, water and any wings already flying.
Cue Which way is everything moving, and how fast?
Why The overall signs show the wind the site is really sitting in¹².
Check the indicators on launch and in the landing field (LZ).
Cue Sock and streamers pointing up the slope; the landing-field sock may differ.
Why If launch disagrees with the overall signs, suspect rotor or a local effect¹².
Watch for several minutes, through more than one cycle, with a wind meter if you have one.
Cue The pattern of gusts, lulls and direction swings.
Why One glance can catch a lull or a gust¹⁷⁵.
Judge the strongest gusts, not the average.
Cue How high the sock swings in the gusts.
Why The pull on the wing grows with the square of the wind¹.
Compare with your limits, ask your instructor, and keep watching while you get ready.
Cue Inside your limits, straight up the slope, steady — and no dust devils.
Why Your instructor sets the limit for the day, and on thermic days the wind changes with every cycle¹⁷.

Common mistake Judging the wind on your face

Symptom: It feels light on launch, but the wing kicks hard as it rises.
Cause: The wind at head height is weaker than a few metres up, and your skin is a poor gauge.
Fix: Use the sock, streamers and a wind meter, and look at the trees and wings higher up⁵⁶.

Common mistake Deciding in a lull

Symptom: You lay out in calm air; a strong cycle arrives just as you inflate.
Cause: You read the wind once instead of watching the pattern.
Fix: Watch several cycles and plan for the strongest gusts you saw¹⁷.

Common mistake Trusting one indicator

Symptom: The sock looks gentle, but your wing behaves as if it is much windier — or the air is rough.
Cause: The sock was sheltered, sitting low in the wind gradient, or in rotor behind an obstacle.
Fix: Cross-check with water, trees, smoke and other wings, and ask why indicators disagree¹².

Instructor's note When the signs disagree

Disagreement is information, not noise. A sock pointing the “wrong” way, or swinging around while the trees nearby bend steadily one way, often means rotor or a sheltered spot. When the picture does not add up, wait and ask.

Questions students ask

What if I can’t see a windsock?

Use everything else — streamers, trees, water, smoke and other wings — and ask your instructor. No clear picture means wait.

The forecast said light wind, but the sock is flying high. Which do I believe?

What you see on site. Station reports are averages and can be minutes old¹⁵, and the terrain can speed the wind up locally²⁵²⁶. See Rotor, venturi and compression.

The sock is hanging limp. Does that mean there is no wind?

Only at the sock. The wind usually gets stronger with height, so your wing may meet a breeze the sock does not show²⁷⁶.

Why are the USHPA and APPI numbers different?

They measure different things. APPI’s 15 km/h9 mph is for its ground-handling tasks; USHPA’s figures are recommended operating limits for rated pilots, with gust limits too. Your instructor’s limit for the day comes first.

Key points

Read direction, strength and steadiness; no single indicator gives all three.
An airport sock at or near horizontal is too windy for a student; site socks differ, so check yours against a wind meter.
Cross-check with trees, water, smoke, birds and other wings; disagreement can mean rotor.
Gusts decide, not the average: the pull grows with the square of the wind.
On thermic days, wait for a steady window: not the gusts, not the lull.
Published limits differ by body; your instructor’s limit for the day comes first.

Ground to Solo is a study aid. Paragliding is learned in person with a qualified instructor at a recognised school; nothing here certifies you to fly.