Definition
An FB is a National Weather Service forecast product that gives predicted wind direction, wind speed, and air temperature at specified altitudes above sea level for selected locations across the United States. Winds are forecast in true direction (degrees from true north) and speed in knots; temperatures are given 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, though winds are not forecast within 1,500 feet of a station's elevation, and temperatures are not forecast for the 3,000 ft level or for any level within 2,500 feet of station elevation.
Plain English
A weather forecast that tells you which way the wind will be blowing, how fast, and how cold or warm the air will be at different altitudes you might fly through.
Context Anchor
Seen in preflight weather planning, especially when choosing a cruising altitude or estimating time and fuel for a cross-country flight.
Derivation
The product was historically called the FD (Forecast Winds and Temperatures Aloft). The identifier was changed to FB when the format was updated to align with international (ICAO) standards. The 'B' has no special meaning on its own — it simply distinguishes the current product from the older FD.
Why Pilots Care
This forecast helps pilots choose the most efficient and safe altitude by showing expected winds and temperatures aloft.
Intuition Check
Do not read this as a surface wind forecast. An FB is about conditions above the ground at specific altitudes.
Example Sentence 1
Before departure, she pulled up the FB and saw a 50-knot headwind at 9,000 feet, so she filed for 6,000 instead.
Example Sentence 2
Winds and temperatures from the FB indicated a strong jet stream at flight level 180.