Winds Aloft

Wind barbs — build one

Direction (from, °True): Speed: kt

The shaft points to where the wind comes from (true north). Feathers sit on the low-pressure side of the flow: for a westerly they point poleward — towards the north in the NH, towards the south in the SH (mirror image).

WAFS wind / temperature charts

Producers: WAFC London and WAFC Washington, from the same global model data used by flight-planning systems (GRIB2).
Levels (charts): FL050, 100, 140, 180, 240, 270, 300, 320, 340, 360, 390, 410, 450 and 530 (varies by provider). The gridded data behind them is what your flight plan uses.
Validity: fixed-time forecasts — 00, 06, 12, 18 UTC. Use the chart closest to the time you will be at that point.
Grid: one barb per point of a regular lat/long grid (spacing depends on the chart scale). Direction is true; speed in knots.
Temperature: whole °C, negative unless marked “+” (e.g. 56 = −56 °C). Compare with ISA to get the ISA deviation for performance.
Isotachs / shading (on some versions) show speed bands — the jet core is the band with the highest speeds.

Pressure level ↔ flight level

Pressure	≈ Flight level	ISA temp	Typical bizjet use
300 hPa	FL300	−44.4 °C	Step-down / descent planning
250 hPa	FL340	−52.4 °C	Initial cruise when heavy
200 hPa	FL390	−56.5 °C	Typical long-range cruise band (FL390–430)
150 hPa	FL450	−56.5 °C	Upper cruise (FL450–510 when light)
100 hPa	FL530	−56.5 °C	Above most bizjet ceilings

ISA: −2 °C per 1,000 ft (−1.98) up to the ISA tropopause at 36,089 ft, then −56.5 °C constant.

FB coded forecast (US “winds and temps aloft”)

Tap a group to decode it. Heights are in feet (MSL); from 18,000 ft up they are flight levels.

Tap a group above.

Rules

DDss(±TT): direction in tens of degrees true, speed in knots, temperature °C.
9900 = light and variable (less than 5 kt).
Speed 100–199 kt: 50 is added to the direction and 100 subtracted from the speed. Direction digits 51–86 therefore mean 100 kt+: 7319 → 230° / 119 kt.
7799 (direction +50, speed “99”) = 199 kt or more.
Above 24,000 ft the minus sign is omitted — all temperatures there are negative.
No wind is forecast within 1,500 ft of station elevation, and no temperature at 3,000 ft or within 2,500 ft of station elevation.

Mean winds aloft — Americas & Atlantic1991–2020 climatology

Tap the map for the mean wind and temperature at that point.

Arrows point downwind (the way the air moves) — length ∝ speed. Seasonal means are much smoother and weaker than any single day: daily jet cores are typically 1.5–2× the mean shown. Data: NCEP/NCAR Reanalysis long-term monthly means (NOAA PSL), 2.5° grid, 250/200/150 hPa.

Why the winds blow that way

Geostrophic wind: away from the equator, the pressure-gradient force is balanced by Coriolis — the wind blows parallel to the isobars/contours, faster where they are packed.
Buys Ballot: back to the wind, low pressure is on the left in the NH and on the right in the SH. Lows turn anticlockwise in the NH and clockwise in the SH; highs the opposite.
Thermal wind: the air is colder towards the poles, so pressure surfaces slope down poleward more and more with height → westerlies increase with height up to the tropopause (jet cores), then decrease above.
Three-cell circulation: surface trade winds blow from the subtropical highs to the ITCZ (NE trades in the NH, SE trades in the SH). Aloft the flow returns poleward and is turned by Coriolis into the subtropical westerly jet at the edge of the Hadley cell (~25–35°).
Near the equator Coriolis vanishes: winds aloft are light and mostly easterly, strongest in the summer hemisphere (monsoon anticyclones aloft) — except the westerly ducts over the equatorial Atlantic and E Pacific in Dec–Mar.
The winter hemisphere has the larger pole–equator temperature contrast → stronger jets, closer to the equator. The whole pattern follows the sun: north in July, south in January.

Seasons × hemispheres at cruise levels

Feature	Dec–Feb (NH winter · SH summer)	Jun–Aug (NH summer · SH winter)
NH subtropical jet	Strong, ~25–30°N: Mexico – Gulf – Florida – Canaries – N Africa. Mean 60–100 kt, days of 150 kt+	Weak/broken, ~40°N
NH polar front jet	Strong, meandering; USA and N Atlantic (35–50°N)	Weak, ~45–55°N (Canada, N Atlantic)
SH subtropical jet	Weaker, ~35–45°S	Strong, ~25–35°S: S Brazil, N Argentina, S Atlantic. Mean 70–80 kt at FL390, days of 120–150 kt
Tropics over S America	Bolivian High (~15–20°S, 60–65°W) and Nordeste trough aloft; SE–S winds over central Brazil	Westerlies reach central Brazil; high moves to N South America
Equatorial Atlantic	Westerly duct — light-to-moderate westerlies aloft, ~5°S–15°N	Easterlies aloft; Tropical Easterly Jet over Africa (~FL450, 5–15°N) tailing into the Atlantic
ITCZ (surface)	Atlantic ~0–5°N; southernmost in Mar–Apr (~2°S–2°N off NE Brazil — NE Brazil rainy season)	Moving to its northernmost (~8–12°N, peak Aug–Sep)

Transition seasons (Mar–May, Sep–Nov) sit in between; the SH jet over southern Brazil already strengthens in Apr–May, the NH jet is still present in Apr — so late autumn (SH) is often the worst time for northbound headwinds to the USA.

Route winds — SBGR ↔ USA / Europemean component, great circle

Route coloured by mean component (blue = tailwind, orange = headwind) over the season's mean wind field.

Mean component by month

Tailwind (+)Headwind (−)

Along the route —

Climatological means for study and seasonal planning only. On a given day the component along these routes can be 3–5× larger (e.g. a 150 kt winter jet over S Brazil or the US East Coast). Plan with the actual forecast winds.

Practice chart — wind/temp FL390invented, not a forecast

Tap any barb to decode it.

Built from the Jun–Aug mean field with a typical daily subtropical jet added over southern Brazil. Temperatures shown every 10°; tap for all.

Wind triangle

True course °

TAS kt

Wind from °T

Wind speed kt

Distance NM

Mach → TAS · ISA deviation

Mach

Flight level

OAT (SAT) °C

TAS = 661.47 × M × √(T / 288.15), T in kelvin (static air temperature). Use the TAS result in the wind triangle above.

Equal-time point (ETP)

Total distance NM

TAS kt

Component to continue (±)

Component to return (±)

ETP from departure = D × GS_return / (GS_continue + GS_return). Enter + for tailwind, − for headwind (for engine-out / depressurisation ETPs use the TAS and level of that scenario). A tailwind towards the destination moves the ETP back towards departure.

Quiz

Progress by area

Sources: ICAO Annex 3; WAFC wind/temperature chart conventions (BoM); NWS/FAA FB format (AC 00-45); NOAA PSL NCEP/NCAR Reanalysis 1991–2020 LTM.