Winds and temperatures Aloft Forecasts (FB) are computer prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations. They are produced 4 times daily for certain stations in the continental United states, Hawaii, Alaska and coastal waters, and the western Pacific Ocean. Wind forecasts are not issued for altitudes within 1500 feet of a location's elevation and no temperatures are forecast for the 3,000 foot level or for any level within 2,500 feet of station elevation. The first two digits in each listing represent the wind direction with reference to true north, coded to the nearest 10 degrees and omitting the final 0. The next two digits represent the wind speed in knots. Wind speeds less than 5 knots are coded 9900 and considered to be “light and variable.”

Forecast wind speeds of 100 through 199 knots are indicated by adding 50 to the coded direction and subtracting 100 from the speed. For example, a forecast of 250 degrees, 145 knots, is encoded as 7545. Forecast wind speeds of 200 knots or greater are indicated as a forecast speed of 199 knots.  Thus, 7799 is decoded as 270 degrees at 199 knots or greater. The two digits following the wind speed and direction show the temperature in degrees Celsius. Temperatures are assumed to be negative above 24,000 feet. Altitudes up to 15,000 ft are referenced to MSL  and altitudes at or above 18,000 ft are referenced to flight levels (FL). Forecasts for intermediate levels should be determined by interpolation.

A Winds and Temperatures Aloft Forecast can help pilots determine the most favorable altitude (based on winds and direction of flight); areas of possible icing (by noting air temperatures of +2 degrees C to -20 degrees C); temperature inversions; and turbulence (by observing abrupt changes in wind direction and speed at different altitudes).

The FB picture above is translated as follows:

DATA BASED ON 041200Z (the date and time observations were collected—4th day of the month at 1200 Zulu)

VALID 041800Z (the beginning date and time when the forecast becomes valid—the 4th day of the month at 1800 Zulu), 

FOR USE (the time period during which the forecast is to be used—1400 thru 2100 Zulu)

TEMPS NEG ABV 24,000 (a reminder that temperatures are negative above 24,000 feet; no minus sign is included in the data columns from 30,000 feet and above)

BIH (reporting station identifier, KBIH—Bishop Airport)

9900 (at 3000 and 6000 ft, winds are less than 5 knots—light and variable

2510+01 (at 9000 ft, winds are 250 degrees at 10 knots; temperature is 1 degree Celsius)

2626-04 (at 12,000 ft, winds are 260 degrees at 26 knots; temperature is minus 4 degrees Celsius)

2646-16 (at 18,000 ft, winds are 260 degrees at 46 knots; temperature is minus 16 degrees Celsius)

2653-28 (at 24,000 ft, winds are 260 degrees at 53 knots; temperature is minus 28 degrees Celsius)

266444 (at 30,000 ft, winds are 260 degrees at 64 knots; temperature is minus 44 degrees Celsius)

266954 (at 34,000 ft, winds are 260 degrees at 69 knots; temperature is minus 54 degrees Celsius)

267265 at 39,000 ft, winds are 260 degrees at 72 knots; temperature is minus 65 degrees Celsius)