Definition
A forecast product that predicts wind direction, wind speed, and air temperature at specific altitudes above mean sea level for selected reporting locations. Winds are given as a three-digit direction (true north reference) and a two-digit speed in knots, followed by temperature in degrees Celsius. Forecasts are issued for standard altitudes such as 3,000, 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet, with wind direction and temperature omitted at altitudes within 1,500 feet of station elevation, and temperature omitted at 3,000 feet.
Plain English
A forecast that tells pilots which way the wind will be blowing, how fast it will be, and how cold the air will be at different altitudes along their route.
Context Anchor
You encounter this during preflight weather planning when choosing an altitude, estimating groundspeed, checking likely headwinds or tailwinds, and considering temperature effects on aircraft performance.
Derivation
The product was historically called 'FD' (Forecast, winds aloft - D for the data type code). It was renamed 'FB' when the format was updated to align with international (WMO) coding standards, where 'FB' designates a wind and temperature aloft forecast.
Why Pilots Care
Pilots consult this forecast to select the most favorable cruising altitude for fuel efficiency, performance, and to avoid unfavorable winds or icing conditions.
Intuition Check
Do not read this as a report of current surface wind. It is a forecast for wind and temperature at selected altitudes above the ground along an area or route.
Example Sentence 1
Before her cross-country flight, she checked the FB to see whether 6,000 or 9,000 feet would give her a better tailwind.
Example Sentence 2
According to the FB, winds at 12,000 feet were expected from the west at 30 knots with a temperature of minus 5 Celsius.