Winds Aloft Forecast (FD) Notes
updated October 2004
obsolete and superseded, retained for archive

The reporting stations can be viewed on an interactive map at
http://aviationweather.gov/products/nws/fdwinds/

The forecast are published by http://aviationweather.gov/
which I think is a subdivision of http://www.noaa.gov/

• The forecast are a guess about what might be happening in the future.  The weather is not an exact science due a multitude of variables, so even the best guessers are somewhat wrong to varying degrees most of the time.
   
• The forecast are for a broad area so you need to do some interpolation for your local based on perceived fudge factors.  All the forecast are centered around an airport with a 3 letter identifier.  The ones for our local are Santa Barbara (SBA) and Fox Field (WJF) near Lancaster (WJF stands for Willy J Fox).
   
• Forecast are issued twice a day 12 hours apart.  To create a forecast, I suspect they use balloon data as well as other information sources like pilot reports.  The balloons go up twice a day at 4 PST or 5 PDT (12Z = 4 am PST & 00Z = 4 pm PST).  The forecast are usually available about 2 hours after the balloons, or by 6 or 7 o'clock depending daylight savings time, but sometimes later or not at all on holidays.
   
• Each forecast issuance covers 3 forecast periods (6, 12, & 24 hours).  Which periods you look at depend on weather it is the morning or evening forecast issuance.
  • Z time (Zulu) is international time using a 24 hour clock referenced to Greenwich England.  The earth spins toward the east, so we need to subtract from Z time to get local time
    • Subtract 8 hours from Z time for local PST
    • Subtract 7 hours from Z time for local PDT
  • For the morning issuance, we look at the
    • 06 hour forecast (17-21Z ~ 9 am to 1 pm PST) for early conditions
    • 12 hour forecast (21-18Z ~1 pm to 10 pm PST) to see the afternoon trend
    • 24 hour forecast (18-17Z ~ 10 pm to 9 am PST) is a reflection of early next morning
  • If you look a the evening issuance, the
    • 06 hour forecast period (05-09Z ~ 9 pm to 1 pm) isn't of much concern to us because we don't fly in the middle of the night
    • 12 hour forecast period (09-18Z ~ 1 am to 10 am) is indicative of early next morning
    • 24 hour forecast period (18-05Z ~ 10 am to 9 pm) covers the next days flying window.
  • It is of vital importance to determine weather you are looking at a morning or evening forecast issuance.  If you're checking in the morning, look to see if the 6 hour forecast says 17-21Z.  If not, the  forecast is for a period that has already elapsed.  If it's not available, you can still use the 12 and 24 hour forecast from last night, but it will be less accurate than the current updated morning guess.
     
• To use a forecast, locate the station you want.
  • Altitude (in 3,000 foot increments) is listed across the top, and the airports are listed vertically on the left.  After confirming the time you are looking at, find the airports on the left that you want (usually SBA and WJF).  If you're flying Ojai or Pine Mountain, your in between, so...
  • 3 data items are coded; Wind direction, Wind Speed, and Temperature in degrees Centigrade
    • The first 2 digits are the direction the wind is coming from rounded to the nearest 10 degrees
      • 9900 / If there is no velocity, then there is no direction, so light and variable is coded as 9900
    • The 3rd and 4th digit represent velocity.  Don't concern yourself too much with the difference between mph and knots because it's all a crude guess with plenty of local variation so the 15% conversion won't make much difference because...
      • If the velocity is over 100 knots, they drop the leading one from the velocity and and add 50 to the direction, so 136 knots from 320 degrees and would be represented as 8236 (first 4 digits)
    • The last 2 digits are temperature in Centigrade.  At 30,000 feet and above, it is assumed to be negative.
  • Wind and temperature are not reported near the surface, so some stations are missing lower wind and or temperature readings.
     
  • Example:  2412-03 would indicate the wind is from 240 degrees at 12 mph and the temperature is minus 3 degrees Celsius.