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Chapter 7. Safety of Flight

Section 1. Meteorology



1. National Weather Service Aviation



Weather service to aviation is a joint effort of the

National Weather Service (NWS), the Federal

Aviation Administration (FAA), the military weather

services, and other aviation oriented groups and

individuals. The NWS maintains an extensive

surface, upper air, and radar weather observing

program; a nationwide aviation weather forecasting

service; and provides limited pilot briefing service

(interpretational). Pilot weather briefings are pro-

vided by personnel at Flight Service Stations

operated by FAA (in Alaska) or by federal contract

facilities (elsewhere in the U.S.). Aviation routine

weather reports (METAR) are taken manually by

NWS, FAA, contractors, or supplemental observers.

METAR reports are also provided by Automated

Weather Observing System (AWOS), Automated

Surface Observing System (ASOS), and Automated

Weather Sensor System (AWSS).


AIM, Para 7

−1−12, Weather Observing Programs.


Aerodrome forecasts are prepared by 122

Weather Forecast Offices (WFOs). These offices

prepare and distribute 625 aerodrome forecasts 4

times daily for specific airports in the 50 States,

Puerto Rico, the Caribbean and Pacific Islands. These

forecasts are valid for 24 or 30 hours and amended as

required. A centralized aviation forecast program

originating from the Aviation Weather Center (AWC)

in Kansas City was implemented in October 1995. In

the conterminous U.S., all inflight advisories,

Significant Meteorological Information (SIGMETs),

Convective SIGMETs, and Airmen’s Meteorological

Information (AIRMET−text bulletins [WA] and

graphics [G−AIRMETs]), and all Area Forecasts

(FAs) (6 areas) are now issued by AWC. FAs are

prepared 3 times a day in the conterminous U.S. and

Alaska (4 times in Hawaii), and amended as required.

Inflight advisories are issued only when conditions

warrant. Winds aloft forecasts are provided for

176 locations in the 48 contiguous States and

21 locations in Alaska for flight planning purposes.

(Winds aloft forecasts for Hawaii are prepared

locally.) All the aviation weather forecasts are given

wide distribution through the Weather Message

Switching Center Replacement (WMSCR) in

Atlanta, Georgia, and Salt Lake City, Utah.


AIM, Para 7

−1−6, Inflight Aviation Weather Advisories.


Weather element values may be expressed by

using different measurement systems depending on

several factors, such as whether the weather products

will be used by the general public, aviation interests,

international services, or a combination of these

users. FIG 7−1−1 provides conversion tables for the

most used weather elements that will be encountered

by pilots.



2. FAA Weather Services


The FAA maintains a nationwide network of

Flight Service Stations (FSSs) to serve the weather

needs of pilots. In addition, NWS meteorologists are

assigned to most ARTCCs as part of the Center

Weather Service Unit (CWSU). They provide Center

Weather Advisories (CWAs) and gather weather

information to support the needs of the FAA and other

users of the system.


The primary source of preflight weather

briefings is an individual briefing obtained from a

briefer at the FSS. These briefings, which are tailored

to your specific flight, are available 24 hours a day

through the use of the toll free number (1−800−WX

BRIEF). Numbers for these services can be found in

the Airport/Facility Directory (A/FD) under “FAA

and NWS Telephone Numbers” section. They may

also be listed in the U.S. Government section of your

local telephone directory under Department of

Transportation, Federal Aviation Administration.


AIM, Para 7

−1−4, Preflight Briefing, explains the types of preflight

briefings available and the information contained in each.

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