12.winds-and-temperatures-aloft. Winds and Temperatures Aloft Forecast (FB)
The Winds and Temperatures Aloft Forecast (FB) is a computer-prepared forecast of wind direction, wind speed, and temperature at specified altitudes for selected locations across the United States. Originally produced by the National Weather Service (NWS) and now generated from the Global Forecast System (GFS) numerical weather model, the FB is one of the most heavily used products in flight planning. It supports decisions about cruise altitude selection, fuel burn, time en route, drift correction, and icing/turbulence risk.
Issuance and Valid Times. The FB is issued four times daily based on 0000Z and 1200Z model runs. Each issuance contains a valid time and a 'for use' window. Pilots should always check the header to confirm the forecast covers the time of the planned flight.
Forecast Levels. The FB provides values at the following standard altitudes, expressed in feet MSL:
- 3,000
- 6,000
- 9,000
- 12,000
- 18,000
- 24,000
- 30,000
- 34,000
- 39,000
- 45,000
- 53,000
Important rules:
- No wind data is forecast for any level within 1,500 feet of the station elevation.
- No temperature data is forecast for the 3,000-foot level or for any level within 2,500 feet of the station elevation.
- Temperatures are always negative above 24,000 feet, so the minus sign is omitted at and above FL300.
Decoding the Format. Each entry is a 4-digit or 6-digit group: DDff or DDffTT.
- DD = true wind direction in tens of degrees (e.g., 27 = 270°).
- ff = wind speed in knots.
- TT = temperature in degrees Celsius.
Example: 2635-08 at 9,000 ft means wind from 260° true at 35 knots, temperature -8°C.
Light and Variable Winds. When the forecast wind speed is less than 5 knots, the group is coded 9900, meaning 'light and variable.'
High-Speed Winds. When forecast wind speed is 100 knots or greater, 50 is added to the direction code and 100 is subtracted from the speed. For example, 7799-58 decodes as: subtract 50 from 77 to get direction 270°, add 100 to 99 to get 199 knots, temperature -58°C. The maximum encoded speed is 199 knots; any forecast 200 knots or greater is encoded as 199.
Worked Example.
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 DEN 2714 2725+00 2640-08 2655-18 2672-30 731147 731856 731960
- 6,000 ft: wind 270° at 14 kt (no temperature given because DEN elevation makes 6,000 ft within 2,500 ft of station).
- 9,000 ft: 270° at 25 kt, temperature 0°C.
- 18,000 ft: 260° at 55 kt, -18°C.
- 30,000 ft: direction 73-50 = 230° at 11 kt; temperature is implicitly negative, so -47°C.
- 39,000 ft: 230° at 19 kt, -60°C.
Practical Use in Flight Planning.
- Altitude selection. Compare wind components at adjacent FB levels to find the most favorable cruise altitude. A 20-knot tailwind versus a 10-knot headwind is a 30-knot ground speed difference.
- Wind correction angle and ground speed. Use the forecast wind to compute heading and ETA on the navigation log.
- Temperature. Required for true airspeed computation, density altitude estimation, and assessing structural icing potential (visible moisture combined with temperatures between roughly +2°C and -20°C).
- Turbulence clues. Large changes in wind direction or speed between adjacent levels (vertical wind shear) suggest turbulence, even when no AIRMET Tango is in effect.
- Jet stream identification. Speeds of 50 knots or more, especially with rapid increases at higher levels, indicate jet stream proximity and possible clear air turbulence.
Limitations. The FB is a forecast, not an observation. Accuracy decreases with forecast age and is reduced in rapidly changing synoptic patterns. It interpolates between standard levels, so actual winds at intermediate altitudes may differ. For the most reliable inflight winds, cross-check with PIREPs, onboard winds-aloft displays, and actual ground speed observed in cruise.
Related Products. The Graphical Forecasts for Aviation (GFA) on aviationweather.gov provide a visual, time-stepped depiction of winds and temperatures aloft and are now the FAA-preferred companion to the alphanumeric FB.