Winds aloft decoder
The winds and temperatures aloft forecast, decoded. Direction, speed and temperature at every altitude level.
Region
Valid in
Levels
Direction is degrees TRUE, not magnetic. A dash means the level is within 1,500 ft of the station and not forecast. Amber marks the over-100-knot encoding. The group as it arrived is under each cell.
The issuance cycle
The Aviation Weather Center issues the bulletin four times per day, based on 0000Z, 0600Z, 1200Z, and 1800Z model runs. Each bulletin contains a 6-hour, 12-hour, and 24-hour forecast. The 6-hour forecast includes temperatures; the 12- and 24-hour forecasts cover the same altitude levels but are less precise because they predict further ahead.
Bulletins are regional. The contiguous US is split into several sections (SLC, MKC, DFW, etc.), each covering a set of reporting stations. This tool handles the bulletin format — paste the data block for your region and it decodes every station row at once.
How this works
- Three rules that carry no marker
- The encoding hides three transformations inside an otherwise plain six-digit number. Above 100 knots the direction digits have 50 added (so 73 means 230°), but nothing in the text says "this is an encoded value." Above FL240 the temperature sign disappears — the value is always negative, but again there is no marker. And 9900 does not mean 990° at 0 knots — it means light and variable. Each one turns a plausible-looking number into a wrong reading if you miss it.
- A blank row is the 1,500-foot rule
- The NWS does not forecast winds within 1,500 ft of the station elevation. A station at 5,000 ft MSL has no entry at 3,000 or 6,000 ft, because both levels are within that buffer. The blank is structural, not a data gap — the forecast model does not produce reliable wind data that close to the surface. This tool keeps the blank and labels it, because whitespace-splitting the row would shift every later group to the wrong altitude column.
- True north, and why it matters here
- Winds aloft directions are true, matching METAR wind. Runway headings are magnetic. The difference matters when you apply the wind to a runway: Denver's magnetic variation is about 8°, and in the far north it can exceed 15°. Using the wind direction against a runway number without correcting for variation adds that error straight into the crosswind calculation.
Worked example
2714+06 2725+00 2735-08 2739-18 731960
- 2714+06
- Wind from 270 degrees at 14 knots, temperature +6°C.
- 2725+00
- Wind from 270 degrees at 25 knots, temperature 0°C.
- 2735-08
- Wind from 270 degrees at 35 knots, temperature −8°C.
- 2739-18
- Wind from 270 degrees at 39 knots, temperature −18°C.
- 731960
- Direction digits 73 minus 50 = 23, which stands for 230 degrees. Speed 19 plus 100 = 119 knots. Temperature is 60°C, and above FL240 the sign is always negative.
Standard altitude levels
The forecast covers ten altitude levels. Below 18,000 ft the levels are MSL altitudes. At and above 18,000 ft they are flight levels (pressure altitude).
| Level | Altitude | Note |
|---|---|---|
| 3,000 | 3,000 ft MSL | Blank if station elevation is above 1,500 ft |
| 6,000 | 6,000 ft MSL | Lowest level for most western stations |
| 9,000 | 9,000 ft MSL | |
| 12,000 | 12,000 ft MSL | |
| 18,000 | FL180 | Above this level, altitudes are flight levels (pressure altitude) |
| 24,000 | FL240 | Last level where temperature sign is given explicitly |
| 30,000 | FL300 | Temperature is always negative above FL240 |
| 34,000 | FL340 | |
| 39,000 | FL390 | |
| 45,000 | FL450 | Highest forecast level |
Frequently asked questions
- What is a winds aloft forecast?
- A winds aloft forecast (also called an FB or FD forecast) predicts wind direction, wind speed, and temperature at standard altitude levels. The NWS issues it for reporting stations across the US. Pilots use it for flight planning: choosing an altitude, estimating groundspeed, and calculating fuel burn.
- How do I read a 6-digit winds aloft group?
- The first two digits are the wind direction in tens of degrees (27 = 270°). The next two are wind speed in knots (14 = 14 kt). The last two are temperature in Celsius (+06 = +6°C). When the direction digits exceed 36, the wind speed is above 100 knots: subtract 50 from the direction and add 100 to the speed.
- What does 9900 mean in a winds aloft forecast?
- The code 9900 means light and variable. The wind has no steady direction and the speed is below a threshold (typically under 5 knots). It replaces the normal direction and speed digits.
- Why is the 3,000-ft row blank?
- The NWS does not forecast winds within 1,500 ft of the station elevation. A station at 5,000 ft MSL will have no data at the 3,000 or 6,000-ft levels because both are within 1,500 ft of the surface.
- Are winds aloft directions true or magnetic?
- Winds aloft directions are in degrees true, the same reference as a METAR wind. Runway headings, by contrast, are magnetic. The difference matters in areas with large magnetic variation.
- How often is the winds aloft forecast updated?
- The NWS issues the forecast four times per day. The 6-hour forecast covers the near term. The 12- and 24-hour forecasts cover the same altitude levels but are less precise because they predict further ahead.
- How do I interpolate winds between two altitudes?
- If you plan to cruise between two forecast levels, interpolate the direction and speed independently. For a cruise at 7,500 ft between the 6,000 and 9,000 ft forecasts, you are halfway, so average both direction and speed. For direction, average the two values (accounting for the 360/0 wraparound). For speed, take the arithmetic mean. The same method works between two stations at the same altitude. This is a Private Pilot written exam topic.
- What does 7799 mean in a winds aloft forecast?
- The code 7799 represents the upper limit of the encoding: a direction of 270 degrees and a speed of 199 knots or more. Winds above 199 knots cannot be individually coded because the two-digit speed field (after adding 100) maxes out at 99 + 100 = 199. At jet stream altitudes the actual speed may be well above 200 knots, but the bulletin can only report 199+.
7799 → 77−50 = 270°, 99+100 = 199+ kt
- How do I use winds aloft to plan a flight?
- After decoding the wind at your planned altitude, use an E6B flight computer or an EFB app to find the wind correction angle and groundspeed. The wind correction angle is the number of degrees you turn into the wind to maintain your desired ground track. The groundspeed is your true airspeed adjusted for the headwind or tailwind component. Both come from the triangle of velocities: wind, true airspeed, and ground track.
This bulletin splits the sky into altitude bands.
A SkyPath print reads altitude the same way — real flight paths over a single airport, each colored by the height it flew, then printed on aluminum.
Not a substitute for an official pre-flight weather briefing.