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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

2. Precautionary statements—IFR conditions, mountain
obscurations, and thunderstorm hazards are described
in this section. Statements made here regarding height
are given in MSL, and if given otherwise, AGL or
ceiling (CIG) will be noted.

Example:
SEE AIRMET SIERRA FOR IFR CONDS AND MTN
OBSCN.
TS IMPLY SEV OR GTR TURB SEV ICE LLWS AND
IFR CONDS.
NON MSL HGTS DENOTED BYAGL OR CIG.

Explanation:
The area forecast covers VFR clouds and weather, so the
precautionary statement warns that AIRMET Sierra should
be referenced for IFR conditions and mountain obscuration.
The code TS indicates the possibility of thunderstorms
and implies there may be occurrences of severe or greater
turbulence, severe icing, low-level wind shear, and IFR
conditions. The final line of the precautionary statement alerts
the user that heights, for the most part, are MSL. Those that
are not MSL will be AGL or CIG.

3. Synopsis—gives a brief summary identifying the
location and movement of pressure systems, fronts,
and circulation patterns.

Example:
SYNOPSIS…LOW PRES TROF 10Z OK/TX PNHDL
AREA FCST MOV EWD INTO CNTRL-SWRN OK BY
04Z. WRMFNT 10Z CNTRL OK-SRN AR-NRN MS FCST
LIFT NWD INTO NERN OK-NRN AR EXTRM NRN MS
BY 04Z.

Explanation:
As of 1000Z, there is a low pressure trough over the
Oklahoma and Texas panhandle area, which is forecast
to move eastward into central southwestern Oklahoma
by 0400Z. A warm front located over central Oklahoma,
southern Arkansas, and northern Mississippi at 1000Z is
forecast to lift northwestward into northeastern Oklahoma,
northern Arkansas, and extreme northern Mississippi by
0400Z.

4. VFR Clouds and Weather—This section lists expected
sky conditions, visibility, and weather for the next 12
hours and an outlook for the following 6 hours.

Example:
S CNTRL AND SERN TX
AGL SCT-BKN010. TOPS 030. VIS 3-5SM BR. 14-16Z
BECMG AGL SCT030. 19Z AGL SCT050.
OTLK…VFR

OK
PNDLAND NW…AGL SCT030 SCT-BKN100.
TOPS FL200.
15Z AGL SCT040 SCT100. AFT 20Z SCT TSRA DVLPG..
FEW POSS SEV. CB TOPS FL450.
OTLK…VFR

Explanation:
In south central and southeastern Texas, there is a scattered
to broken layer of clouds from 1,000 feet AGL with tops at
3,000 feet, visibility is 3 to 5 sm in mist. Between 1400Z and
1600Z, the cloud bases are expected to increase to 3,000 feet
AGL. After 1900Z, the cloud bases are expected to continue
to increase to 5,000 feet AGL and the outlook is VFR.

In northwestern Oklahoma and panhandle, the clouds are
scattered at 3,000 feet with another scattered to broken layer
at 10,000 feet AGL, with the tops at 20,000 feet. At 1500
Z, the lowest cloud base is expected to increase to 4,000
feet AGL with a scattered layer at 10,000 feet AGL. After
2000Z, the forecast calls for scattered thunderstorms with
rain developing and a few becoming severe; the CB clouds
will have tops at flight level 450 or 45,000 feet MSL.

It should be noted that when information is given in the area
forecast, locations may be given by states, regions, or specific
geological features such as mountain ranges. Figure 12-12
shows an area forecast chart with six regions of forecast,
states, regional areas, and common geographical features.

Inflight Weather Advisories
Inflight weather advisories, which are provided to en route
aircraft, are forecasts that detail potentially hazardous
weather. These advisories are also available to pilots prior to
departure for flight planning purposes. An inflight weather
advisory is issued in the form of either an AIRMET, SIGMET,
or convective SIGMET.

AIRMET
AIRMETs (WAs) are examples of inflight weather advisories
that are issued every 6 hours with intermediate updates
issued as needed for a particular area forecast region. The
information contained in an AIRMET is of operational
interest to all aircraft, but the weather section concerns
phenomena considered potentially hazardous to light aircraft
and aircraft with limited operational capabilities.

An AIRMET includes forecast of moderate icing, moderate
turbulence, sustained surface winds of 30 knots or greater,
widespread areas of ceilings less than 1,000 feet and/or
visibilities less than three miles, and extensive mountain
obscurement.

 

12-12