Winds and Temperatures Aloft (FBs) are computer prepared forecasts for specific locations in the contiguous U.S. and a network of locations in Alaska and Hawaii based on the North American Mesoscale (NAM) forecast model run [Figure 1 ]
"FDWinds," now "FBwinds," are produced in both a textual and graphical format
This information aids the pilot in:
Determining the most favorable altitude based on winds and direction of flight
Identifying areas of possible aircraft icing , by noting air temperature of +2°C to -20°C, and temperature inversions
Predicting turbulence by observing abrupt changes in wind direction and speed at different altitudes
Wind and Temperature Aloft Forecast (FB) Periods
Winds and Temperatures Aloft Forecast Header
FBs are produced by the NWS National Centers for Environmental Prediction (NCEP)
Issued 4 times daily, valid for the time stated on the chart [Figure 2 ]
If the scheduled forecast is delayed, the existing valid forecast based on the earlier 6-hourly data can be used until a new forecast is transmitted
FB data is always forecasted, vice observed
Amendments are not issued to winds aloft forecasts
Issued for 9 regions: (6 CONUS and 3 OCONUS)
Wind and Temperature Aloft Forecast (FB) Periods
Winds and Temperatures Aloft Forecast Stations
Winds and Temperatures Aloft Forecast Header
There are two main elements to a winds and temperatures aloft forecast:
Forecast Levels
Issued for a variety of altitudes based on location [Figure 4 ]
"FT" indicates the levels of the wind and temperatures data
A four-digit group shows wind direction in tens of degrees, the second two are wind speed in knots
Altitudes up to 15,000' the levels are true altitude (references to MSL)
Altitudes at or above 18,000' the levels are pressure altitudes (references to FL)
The symbolic form of the forecasts is DDff+TT in which:
DD is the wind direction
ff the wind speed, and
TT the temperature
Forecast Levels
Winds and Temperatures Aloft Forecast Data
No winds are forecasted within 1,500' of station elevation
Winds are forecasted true, indicated in tens of degrees (two digits) with reference to true north and wind speed is given in knots (two digits)
If forecast speed is less than 5 knots, the coded group is 9900 which means, "light and variable"
990012: winds are light and variable, temperature 12°C
If forecast speed is greater than 100 knots, 100 is subtracted from the wind speed and 50 is added to the wind direction
731960:
Step 1: 73-50 = 23 or 230
Step 2: 19 + 100 = 119
Result: 230@119 (temperature -60°C)
If the wind speed forecast to be 200 knots or greater, the wind group is coded as 99 knots
189960: 180@200+ (temperature -60°C)
No temperatures are forecasted within 2,500' AGL of station elevation
No temperatures are forecasted in the 3,000' column
A six-digit group includes forecast temperatures in degrees Celsius
192832: the last two digits show 32°C for the temperature but remember above 24,000' the negative sign is excluded
Winds and Temperatures Aloft Forecast Data
