Winds & Temperatures Aloft

Winds & Temperatures Aloft

Introduction:

  • 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

 

Winds and Temperatures Aloft Forecast
Figure 1: Winds and Temperatures Aloft Forecast

Issuance & Validity:

    • 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
Wind and Temperature Aloft Forecast (FB) Periods
Figure 2: Wind and Temperature Aloft Forecast (FB) Periods
Winds and Temperatures Aloft Forecast
Figure 3: Winds and Temperatures Aloft Forecast Header

Elements:

Header:

  • “FD” indicates a Winds and Temperatures Aloft
  • “FD1US1” is a standard line regardless of reported region
  • Data is collected at the date time group (DTG) listed
    • “DATA BASED ON: 121800Z:” Data is based on the 12th day of the month, 1800Z
  • Valid at the “FOR USE” times listed
    • “FOR USE: 2000-0300Z:” for use between 2000Z and 0300Z
  • “TEMPS NEG ABOVE 24000” is a standard line
    • Since temperatures above 24,000′ are always negative, the minus sign is omitted

Forecasted Data:

    • 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
Winds and Temperatures Aloft Forecast Altitudes
Figure 4: Forecast Levels
    • 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
  • Winds:
    • 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)
      • 2022: 200@22 knots
    • 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 a wind direction is coded between 51 and 86, the wind speed is 100 knots or greater
      • Subtract 50 from the wind and add 100 to the wind
      • 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: 230@200+ (temperature 60°C)
  • Temperatures:
    • 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 Altitudes
Figure 5: Winds and Temperatures Aloft Forecast Data

Example:

  • The following is a typed out version of the example pictured above
  • Move your mouse over the numbers to show what they mean decoded
  • The numbers in red were changed for the purpose of citing a wider range of examples
  • Additional explanation can be found at AviationWeather.gov

FD1US1
DATA BASED ON 131800Z
VALID 140000Z FOR USE 2000-0300Z. TEMPS NEG ABV 24000
FT 3000 6000 9000 12000 18000 24000 30000 34000 39000
EYW 2022 2028+16 2023+12 2122+06 2027-05 2126-16 212830 232340 233153
JAX 2136 2237+15 2237+10 2239+05 2334-06 2238-15 234130 245141 246153
MIA 2212 2221+16 2019+10 2125+06 2126-05 2227-15 242631 242540 242653
MLB 2221 2133+15 2036+09 2131+05 2239-06 2233-16 243230 243641 244553
PFN 3105 9900+15 3012+09 2514+04 3109-05 2612-17 231833 223743 236453
PIE 2219 2317+16 2218+10 2118+05 2321-05 2321-16 243731 234541 235152
TLH 3212 2822+15 2921+10 2913+06 3016-06 2616-17 252132 234342 246753
ATL 0733 0925+14 0717+09 0714+04 0510-07 0409-18 200934 201544 212654
CSG 0724 0611+14 0412+09 0512+05 3511-07 3312-18 231133 221243 232954
SAV 1730 1829+14 1831+10 1732+05 1930-07 2037-17 223231 244042 255853
HAT 9900 2607+13 2514+09 2616+04 2413-08 2515-19 263234 245143 256556
ILM 1708 1907+14 2214+09 2319+04 2320-08 1920-18 202833 223843 235156
RDU 1309 9900+13 2309+08 2417+04 2314-08 2415-19 242734 234144 235656
CAE 1323 1320+14 1417+09 1513+04 1717-08 1920-18 192832 203043 212956
CHS 1624 1825+14 1926+09 1827+05 1923-07 1928-18 214032 223742 234154
FLO 1418 1315+14 1716+09 1916+04 2017-08 1922-18 203033 213743 224056
GSP 0618 1014+14 1209+09 1408+03 1306-07 9900-19 191934 203444 213456
2XG 1921 2024+15 2028+09 2130+05 2240-06 2237-16 223631 731960 779941

Conclusion:

  • The FAA’s Advisory Circular (AC), Aviation Weather Services: Advisory Circular, AC 00-45G, Change 1, can be downloaded for free on their website here or a paper copy may be ordered from Amazon here

References: