Chapter 27
Forecasts
FB Wind and Temperature Aloft Forecasts are computer-prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations.
27.2.1.1 FB Wind and Temperature Aloft Forecast Issuance
The NWS NCEP produces scheduled FB Wind and Temperature Aloft Forecasts four times daily for specified locations in the CONUS, the Hawaiian Islands, Alaska and coastal waters, and the western Pacific Ocean.
Amendments are not issued to the forecasts. Wind forecasts are not issued for altitudes within 1,500 ft of a location’s elevation. Temperature forecasts are not issued for altitudes within 2,500 ft of a location’s elevation.
27.2.1.1.1 FB Wind and Temperature Aloft Forecast Text Format
The text format for the FB Wind and Temperature Aloft Forecast uses the symbolic form DDff+TT in which DD is the wind direction (true), ff is the wind speed, and TT is the temperature.
Wind direction is indicated in tens of degrees (two digits) with reference to true north and wind speed is given in knots (two digits). Light and variable wind or wind speeds of less than 5 kt are expressed by 9900. Forecast wind speeds of 100 through 199 kt are indicated by adding 50 to the first two digits of the wind direction and subtracting 100 from the speed. For example, a forecast of 250°, 145 kt, is encoded as 7545. Forecast wind speeds of 200 kt or greater are indicated as a forecast speed of 199 kt. For example, 7799 is decoded as 270° at 199 kt or greater.
Temperature is indicated in degrees Celsius (two digits) and is preceded by the appropriate algebraic sign for the levels from 6,000 through 24,000 ft. Above 24,000 ft, the sign is omitted since temperatures are always negative at those altitudes.
The product header includes the date and time observations were collected, the forecast valid date and time, and the time period during which the forecast is to be used.
27.2.1.1.2 FB Wind and Temperature Aloft Forecast Coding Example
Sample winds aloft text message:
DATA BASED ON 010000Z VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000 FT 3000 6000 9000 12000 18000 24000 30000 34000 39000 MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 750252
Sample message decoded:
DATA BASED ON 010000Z
Forecast data is based on computer forecasts generated the 1st day of the month at 0000 UTC.
VALID 010600Z FOR USE 0500-0900Z. TEMPS NEG ABV 24000
The valid time of the forecast is the 1st day of the month at 0600 UTC. The forecast winds and temperatures are to be used between 0500 and 0900 UTC. Temperatures are negative above 24,000 ft.
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
FT indicates the altitude of the forecast.
MKC 9900 1709+06 2018+00 2130-06 2242-18 2361-30 247242 258848 750252