Winds Aloft Decoder
Paste an FB Winds and Temperatures Aloft forecast to decode the forecast wind direction, wind speed and temperature at each altitude.
How to decode winds aloft
The coded FB Winds and Temperatures Aloft product provides forecast wind direction, wind speed and temperature for specified altitudes and locations. Wind direction is referenced to true north and wind speed is reported in knots.
FB winds aloft code format
The basic coded form is DDff+TT. DD represents wind direction in tens of degrees, ff represents wind speed in knots, and TT represents temperature in degrees Celsius.
For example, 1709+06 represents wind from 170 degrees true at 9 knots with a temperature of +6 degrees Celsius.
What does 9900 mean in winds aloft?
The code 9900 indicates light and variable wind or a forecast wind speed of less than 5 knots. It should not be interpreted as a literal wind direction of 990 degrees.
Winds of 100 to 199 knots
High wind speeds use a special encoding rule. For forecast speeds from 100 through 199 knots, 50 is added to the encoded wind-direction value and 100 is subtracted from the wind speed.
For example, 7545 represents 250 degrees true at 145 knots: subtract 50 from 75 to recover direction code 25, then add 100 to the encoded speed of 45 knots.
Winds of 200 knots or greater
Forecast wind speeds of 200 knots or greater are coded as 199 knots. The decoder identifies this as 199 knots or greater rather than reporting an exact 199-knot forecast.
Temperature codes
From 6,000 through 24,000 feet, forecast temperature includes an explicit plus or minus sign. Above 24,000 feet the sign is omitted because temperatures are represented as negative.
Thus 247242 at 30,000 feet represents wind from 240 degrees true at 72 knots and a temperature of -42 degrees Celsius.
Forecast header
The FB text product identifies when the forecast data were based on, the forecast valid time and the period during which the forecast is intended for use.
Altitude columns
The FT line lists forecast altitudes. Each coded group in the station row corresponds positionally to one of those altitude columns. A station row is invalid when the number of forecast groups does not match the altitude header.
About the FB product
Modern flight-planning systems generally use more detailed gridded numerical weather-model data. The traditional coded FB Winds and Temperatures Aloft product is an older text format, but it remains useful for interpreting legacy and published winds-aloft forecasts.
For observed aerodrome weather, use the METAR Decoder. Terminal aerodrome forecasts can be decoded with the TAF Decoder.