IRFP-01
Metro Review
F. Winds Aloft Forecast (FD) 21.1.1.5.2
Fig 30: Winds Aloft
Forecast (FD)
1. Teletype report, based on observed (balloon) information
transmitted twice a day
a. Teletype identifier is “FD”
b. The total forecast is usable for 15 hours
c.
Broken into two segments with the forecast periods given at
the beginning of each segment
(1) Valid time indicates that these conditions should exist
specifically at this time
(2) “For use” times mean that these conditions should exist
through this period as the average conditions
2. Wind and Temperature coding/decoding rules
a. Wind normally given with a series of 4 digits
(1) First 2 digits indicate direction wind is from (true)
(2) Second 2 digits depict the wind speed in knots
b. Temperature follows wind information in degrees Celsius
(1) Above or below 0 degrees indicated with a + or -
(2) All temperatures above 24,000 ft MSL are below zero so
the minus sign is dropped
c.
Exceptions
(1) Variable winds indicated by “99” for direction
(2) Forecast winds less than 5 kts indicated by “9900” and
read as “light and variable”
(3) If wind speeds exceed 100 kts, 100 is subtracted from the
wind speed and 50 is added to the direction, e.g., a wind
from 230 at 145 kts would be encoded as 7345
(4) Wind speeds in excess of 200 kts would be encoded at
199 kts, e.g., 7399 would be 230 degrees at 199 kts
3. Temperature decoding/encoding rules
a. Temperature and wind are sometimes omitted from the
forecast
(8-97) Original
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