Winds Aloft Chart
A winds aloft forecast reports wind direction and speed at specific altitudes using a 4-digit code, separate from the surface wind used for runway crosswind.
Decoding the Four-Digit Wind Group
Standard case: 2735
27 → 270° true | 35 → 35 knots
The first pair is direction in tens of degrees, the second pair is speed in knots. Multiply the first pair by ten and read the second directly. This group means the wind at that level is forecast from 270 degrees true at 35 knots.
Above 100 knots: 7521
75 − 50 = 25 → 250° true | 21 + 100 = 121 knots
Four digits cannot hold a three-digit speed, so speeds of 100 knots or more are signalled by adding 50 to the direction pair. Any direction figure above 36 is impossible in reality, which makes the overflow unambiguous: subtract 50 from the direction and add 100 to the speed. A group of 9900 is the other special case and means light and variable, under 5 knots.
A Sample Forecast Read Level by Level
Reading a station's levels in sequence shows the pattern that matters most for planning: wind speed climbs and direction veers steadily with altitude.
| Level | Coded group | Direction | Speed | Temp | Reading |
|---|---|---|---|---|---|
| 3,000 ft | 2512 | 250° | 12 kt | – | No temperature below 2,500 ft above station |
| 6,000 ft | 2620+04 | 260° | 20 kt | +4°C | Speed picking up with height |
| 9,000 ft | 2732-02 | 270° | 32 kt | −2°C | Typical cruise level for a light single |
| 12,000 ft | 2843-08 | 280° | 43 kt | −8°C | Wind has veered and nearly doubled since 3,000 ft |
Between 3,000 and 12,000 feet this wind veers 30 degrees clockwise and more than triples in speed. That is ordinary: surface friction slows and backs the lowest layer, and the effect disappears with height. It is also why a surface report tells you nothing about cruise, and why climbing 3,000 feet to find a better wind is a real planning option on a long leg.
Upper Winds Against Surface Reports
The two products answer different questions and are not interchangeable: one plans the cruise, the other decides the runway.
Winds aloft (FB)
Forecast, upper airA forecast of wind and temperature at fixed altitudes above named stations, issued a few times daily and valid for stated periods. It answers what the wind will do to your groundspeed and heading en route. It says nothing useful about the runway, because the lowest level is usually 3,000 ft.
Surface observation
METAR, right nowA measurement of what the wind is doing at one airport right now, taken about ten metres above the ground. It answers what crosswind the runway faces. It says nothing about cruise, because surface wind and wind at 9,000 ft frequently differ by 40 degrees and 30 knots.
Both express direction in degrees true, which is the one thing they share and the one thing most often forgotten. The surface product is decoded on the observation wind reader, and the crosswind it produces on your runway comes from the surface crosswind calculator.
Applying Upper Winds En Route
Upper winds feed two numbers in the flight plan: the heading needed to hold each leg's course and the groundspeed that determines time and fuel.
Take the forecast for the level nearest your cruising altitude, interpolating between levels where your altitude sits between them, and use it with the true course for the leg. The wind gives a correction angle to hold and a groundspeed to plan against, and both change at every turn because the angle between course and wind changes even when the wind does not.
Two habits make forecast winds more useful than they first appear. Compare your achieved groundspeed on the first leg with what was planned, and apply the same proportional error to the remaining legs, forecasts tend to be wrong consistently rather than randomly. And check whether a different altitude offers a materially better wind before departure, since the gradient shown in the table above can make 3,000 feet of climb worth ten knots of groundspeed. Both numbers come out of the wind correction angle calculator, and the flight computer page shows the same triangle solved mechanically.
Winds Aloft Questions
How often are winds aloft forecasts updated?
Winds aloft forecasts are issued four times a day in the United States, based on the 00Z, 06Z, 12Z, and 18Z model runs, with each issue carrying several valid periods for different parts of the day. A forecast can therefore be several hours old and still be the current one. Check the valid period rather than the issue time, because a product issued recently may be forecasting a window that has already passed.
Why do wind speeds over 100 knots use a different code?
The group has only four digits, so speeds of 100 knots or more will not fit alongside a three-digit direction. The convention adds 50 to the two-digit direction pair to signal the overflow: a direction figure between 51 and 86 means subtract 50 from it and add 100 to the speed. Since real directions only run to 36, anything above that is unambiguous. This only appears at high altitudes where jet stream winds live.
Is winds aloft data the same as what ForeFlight shows on a route?
It comes from the same underlying model but is presented very differently. The text FB product gives fixed altitudes at named stations, so a route between two stations needs interpolation in both position and height. Electronic flight bag applications interpolate the model grid directly along your actual route and altitude, which is why their numbers differ slightly from what the coded text implies.
Do winds aloft forecasts include temperature?
Yes, at every level except the lowest. The two digits following the wind group are the temperature in Celsius, negative unless a plus sign appears, and above 24,000 feet the sign is dropped entirely because temperatures there are always negative. Temperature is omitted for levels within 2,500 feet of the station elevation, which is why the 3,000 ft line often carries a bare four-digit group.
How accurate are winds aloft forecasts close to departure time?
Reasonably good for direction, less so for speed. A forecast a few hours old typically has direction within 20 degrees and speed within 10 knots at mid altitudes, which is enough for flight planning. Accuracy degrades near terrain, in unstable air, and around frontal boundaries. The practical check is comparing forecast groundspeed against what you actually achieve on the first leg, then adjusting the remaining legs.