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Pilot's Handbook of Aeronautical Knowledge
Aviation Weather Services

Aviation Forecasts

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Pilot's Handbook of Aeronautical Knowledge

Preface

Acknowledgements

Table of Contents

Chapter 1, Introduction To Flying
Chapter 2, Aircraft Structure
Chapter 3, Principles of Flight
Chapter 4, Aerodynamics of Flight
Chapter 5, Flight Controls
Chapter 6, Aircraft Systems
Chapter 7, Flight Instruments
Chapter 8, Flight Manuals and Other Documents
Chapter 9, Weight and Balance
Chapter 10, Aircraft Performance
Chapter 11, Weather Theory
Chapter 12, Aviation Weather Services
Chapter 13, Airport Operation
Chapter 14, Airspace
Chapter 15, Navigation
Chapter 16, Aeromedical Factors
Chapter 17, Aeronautical Decision Making

Appendix

Glossary

Index

5. Forecast wind—the wind direction and speed forecast
are given in a five digit number group. The first three
indicate the direction of the wind in reference to true
north. The last two digits state the windspeed in knots
as denoted by the letters "KT." Like the METAR,
winds greater than 99 knots are given in three digits.
6. Forecast visibility—given in statute miles and may
be in whole numbers or fractions. If the forecast is
greater than six miles, it will be coded as "P6SM."

7. Forecast significant weather—weather phenomena are
coded in the TAF reports in the same format as the
METAR. If no significant weather is expected during
the forecast time period, the denotation "NSW" is
included in the "becoming" or "temporary" weather
groups.

8. Forecast sky condition—given in the same manner
as the METAR. Only cumulonimbus (CB) clouds are
forecast in this portion of the TAF report as opposed
to CBs and towering cumulus in the METAR.

9. Forecast change group—for any significant weather
change forecast to occur during the TAF time period,
the expected conditions and time period are included
in this group. This information may be shown as from
(FM), becoming (BECMG), and temporary (TEMPO).
"FM" is used when a rapid and significant change,
usually within an hour, is expected. "BECMG" is used
when a gradual change in the weather is expected over
a period of no more than 2 hours. "TEMPO" is used
for temporary fluctuations of weather, expected to last
less than one hour.

10. Probability forecast—a given percentage that describes
the probability of thunderstorms and precipitation
occurring in the coming hours. This forecast is not
used for the first 6 hours of the 24-hour forecast.

Example:
TAF
KPIR 111130Z 1112/1212
TEMPO 1112/1114
FM1500 16015G25KT P6SM SCT040 BKN250
FM0000 14012KT P6SM BKN080 OVC150 PROB40 0004
3SM TSRA BKN030CB
FM0400 1408KT P6SM SCT040 OVC080
TEMPO 0408 3SM TSRA OVC030CB
BECMG 0810 32007KT=

Explanation:
Routine TAF for Pierre, South Dakota…on the 11th day
of the month, at 1130Z…valid for 24 hours from 1200Z
on the 11th to 1200Z on the 12th…wind from 150° at 12
knots…visibility greater than 6 sm…broken clouds at 9,000
feet…temporarily, between 1200Z and 1400Z, visibility 5 sm
in mist…from 1500Z winds from 160° at 15 knots, gusting
to 25 knots visibility greater than 6 sm…clouds scattered
at 4,000 feet and broken at 25,000 feet…from 0000Z wind
from 140° at 12 knots…visibility greater than 6 sm…clouds
broken at 8,000 feet, overcast at 15,000 feet…between 0000Z
and 0400Z, there is 40 percent probability of visibility 3
sm…thunderstorm with moderate rain showers…clouds
broken at 3,000 feet with cumulonimbus clouds…from
0400Z…winds from 140° at 8 knots…visibility greater
than 6 miles…clouds at 4,000 scattered and overcast at
8,000…temporarily between 0400Z and 0800Z…visibility 3
miles…thunderstorms with moderate rain showers…clouds
overcast at 3,000 feet with cumulonimbus clouds…becoming
between 0800Z and 1000Z…wind from 320° at 7 knots…end
of report (=).

Area Forecasts (FA)

The FA gives a picture of clouds, general weather conditions,
and visual meteorological conditions (VMC) expected over
a large area encompassing several states. There are six areas
for which area forecasts are published in the contiguous 48
states. Area forecasts are issued three times a day and are
valid for 18 hours. This type of forecast gives information
vital to en route operations, as well as forecast information
for smaller airports that do not have terminal forecasts.

Area forecasts are typically disseminated in four sections and
include the following information:
1. Header—gives the location identifier of the source of
the FA, the date and time of issuance, the valid forecast
time, and the area of coverage.
Example:
DFWC FA 120945
SYNOPSIS AND VFR CLDS/WX
SYNOPSIS VALID UNTIL 130400
CLDS/WX VALID UNTIL 122200…OTLK VALID
122200-130400
OK TX AR LA MS AL AND CSTL WTRS

Explanation:
The area forecast shows information given by Dallas Fort
Worth, for the region of Oklahoma, Texas, Arkansas,
Louisiana, Mississippi, and Alabama, as well as a portion of the
Gulf coastal waters. It was issued on the 12th day of the month
at 0945. The synopsis is valid from the time of issuance until
0400 hours on the 13th. VFR clouds and weather information
on this area forecast are valid until 2200 hours on the 12th and
the outlook is valid until 0400 hours on the 13th.

 

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