Chapter 3, Overview of Aviation Weather Information 3-1
3 Overview of Aviation Weather
Information
3.1 Introduction
Title 14 of the Code of Federal Regulations (14 CFR) § 91.103 states the requirements for preflight action
for 14 CFR part 91 operations. According to 14 CFR § 91.103, each pilot-in-command (PIC) shall, before
beginning a flight, become familiar with all available information concerning the flight, including weather
reports and forecasts.
This handbook describes the weather products primarily produced by the NWS. There is an ever-expanding
suite of weather products available on the internet, weather applications (apps) for phones and tablets, as
well as commercial Electronic Flight Bags (EFB) . Pilots and operators should consult with their Principal
Operations Inspector (POI) or their service provider when in doubt about the content and use of new weather
products. Note that the FAA does not certify internet providers of aviation weather services.
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3.2 Use of Aviation Weather Information
3.2.1 Understanding Weather Forecasts
To forecast means to make a prediction about the future state of something. In weather forecasting, the
meteorologist is trying to predict the future state of the atmosphere. There are many different types of
weather forecasts that exist, and we want to cover a basic distinction between deterministic and probabilistic
forecasts.
• A deterministic forecast is one in which forecasters provide only a single solution. For example,
“tonight’s low will be 31 degrees Fahrenheit (°F),” “0.30 inches of rain will fall tomorrow,” or
“thunderstorms will happen at 3 pm tomorrow.”
• A probabilistic forecast is one in which forecasters convey uncertainties by expressing forecasts
as probabilities of various outcomes. For example, “the probability that tonight’s low will be
below 32 °F is 40 percent,” “the probability of receiving at least 0.25 inches of rain tomorrow is
60 percent,” or “the probability of thunderstorms for tomorrow afternoon is 70 percent.”
Probabilistic forecasts allow meteorologists to acknowledge and express the fact that weather forecasts
contain uncertainty, especially as you go out further in time. However, it is important that a probabilistic
forecast has reliability (e.g., if the forecast of thunderstorms for a particular day, time, and location is
70 percent, then thunderstorms do in fact occur seven times out of ten).
3.2.2 Product Latency
With few exceptions, all weather information and products have latency. Latency is the element of data
age. The total latency of weather information and products includes the total time between the actual
occurrence of the phenomenon, the data collection, processing, transmittal, and the display or application
of the information in the cockpit, on the pilot’s EFB, or other publication for use. It is important to be aware
of the product time or “valid until” time on the particular data link information displayed in the cockpit or
EFB. The amount of latency may limit the use or application of the information or product.
An example of weather information without latency is the wind direction when looking at the windsock
along the runway. However, the wind reported in the Automated Weather Observing System ( AWOS) or
Automated Surface Observing System (ASOS) broadcast has a latency of up to 3 minutes. Why? While the
AWOS and ASOS wind (direction and speed) is continuously being recorded by the AWOS/ASOS system
processor, the reported wind is the most recent average of the direction and speed over the past two minutes.
That 2-minute average is then updated once a minute for the radio or telephone broadcast.
Onboard aircraft radar has minimal latency, while NEXRAD data has a latency of 5 to 15 minutes or more
with weather apps and data uplink services. This is why NEXRAD data is used for broad strategic avoidance
of thunderstorms and never used to navigate through thunderstorms.
3.2.3 Additional Use Information
Details on the use of both government and commercial aviation weather information are discussed in the
AIM, Chapter 7, Section 1, Paragraph 7-1-3, Use of Aviation Weather Products. Items discussed include:
• Approved sources for aviation weather information,
• The development of new products through the FAA’s Next Generation Air Transportation System
(NextGen) Aviation Weather Research Program (AWRP),
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• The use of new products to meet regulatory requirements, and
• The use of weather services and products provided by entities other than the FAA, the NWS, or
their contractors.
3.3 Obtaining Weather Information
3.3.1 Weather Briefings
Prior to every flight, pilots should gather all information vital to the nature of the flight. This includes a
weather briefing obtained by the pilot using online weather resources, a dispatcher, or Flight Service.
Historically, Flight Service has been the primary source for obtaining preflight briefings. Today, increasing
numbers of pilots are using online weather resources to obtain weather information through government or
commercial providers. Pilots may receive a regulatory compliant briefing without contacting Flight Service.
Pilots who prefer to contact Flight Service are encouraged to conduct a self -briefing prior to calling.
Conducting a self -briefing before contacting Flight Service provides familia rity of w eather conditions
applicable to the route of flight and promotes a better understanding of weather information.
To obtain an appropriate weather briefing, pilots need to know which of the three types of briefings is
needed for the flight—standard, abbreviated, or outlook. Other necessary information includes whether the
flight will be conducted under VFR or IFR, aircraft identification and type, departure point, and the
estimated time of departure, desired flight altitude, route of flight, destination, and estimated time en route.
If the briefing updates previously received information, the time of the last briefing is also important.
The information is entered into a flight plan form. When using the route brief feature in the Flight Service
Pilot Web Portal (see Appendix G) or speaking to an FSS specialist, the type of weather briefing is recorded.
If necessary, the information can be referenced later to file or amend a flight plan. It can also be used when
an aircraft is overdue or is reported missing. All briefings provided by Flight Service (online or voice) are
time-stamped and archived for 45 days.
Pilots can make a final weather check immediately before departure using online weather apps, when
possible.
3.3.1.1 Standard Briefing
A standard briefing provides a complete weather picture and is the most detailed of all briefings. It includes
conditions and significant weather information that may influence the pilot in planning, altering, or
cancelling a proposed route or flight. A standard briefing provides the following information (if applicable
to the route of flight) in sequential order . However, the adverse conditions, VNR, and synopsis elements
may be combined and presented in any order when it helps to better describe the conditions:
• Adverse Conditions. This includes significant weather and/or aeronautical information about
adverse conditions that may influence a decision to cancel or alter the route of flight (e.g., hazardous
weather conditions, airport closures, or air traffic delays). Pilots should also be alert for any reported
or forecast icing if the aircraft is not certified for operating in icing conditions. Flying into areas of
icing or weather below minimums could have disastrous results.
• VFR Flight Not Recommended (VNR). When VFR flight is proposed and sky conditions or
visibilities are present or forecast, surface or aloft, that, in the briefer’s judgment, would make flight
under VFR doubtful, the briefer will describe the conditions, describe the affected locations, and
use the phrase “VFR flight not recommended.” This recommendation is advisory in nature. The
final decision as to whether the flight can be conducted safely rests solely with the pilot. Upon
receiving a “VFR flight not recommended” statement, the non-IFR rated pilot will need to make a
“go or no go” decision. This decision should be based on weighing the current and forecast weather
Chapter 3, Overview of Aviation Weather Information 3-4
conditions against the pilot ’s experience and ratings. The aircraft ’s equipment, capabilities , and
limitations should also be considered. This advisory is not provided via the internet.
• Synopsis. A brief statement describing the type, location, and movement of weather systems and/or
air masses that might affect the proposed flight.
• Current (Latest) Conditions. This portion of the briefing contains the current (latest reported or
received) surface weather summarized from all available resources , including observations,
PIREPs, and satellite and radar data along the route of flight. If the departure time is more than two
hours away, current conditions will not be included in the briefing unless the pilot specifically
requests the information.
• En Route Forecast. Forecast en route conditions for the proposed route are summarized in logical
order (i.e., departure/climb out, en route, and descent ). Heights are above mean sea level (MSL),
unless the contractions “AGL” or “CIG” are denoted, indicating that heights are above ground.
• Destination Forecast. The destination forecast for the planned estimated time of arrival (ETA).
Any significant changes within 1 hour before and after the planned arrival are included.
• Winds and Temperatures Aloft. Forecast winds aloft will be provided in knots and tens of degrees
and referenced to true north. The briefer will interpolate wind directions and speeds between levels
and stations as necessary to provide expected conditions at planned altitudes. (Heights are MSL.)
Temperature information will be provided on request.
• Notice to Airmen (NOTAM), ATC Delays, and Other Information. Refer to the AIM Chapter 7,
Section 1, Paragraph 7-1-5, Preflight Briefing, subparagraphs b8 through b10 for a complete
description of this part of the briefing. Also refer to the AIM Chapter 5, Section 1, Paragraph 5-1-
3, Notice to Airmen System, for a complete description of all NOTAM types.
3.3.1.2 Abbreviated Briefing
An abbreviated briefing is a shortened version of the standard briefing. It can be requested when a departure
has been delayed or when specific weather information is needed to update a previous standard briefing.
Pilots who prefer to contact Flight Service are encouraged to conduct a self -briefing prior to calling.
Conducting a self -briefing before contacting Flight Service provides familiarity of weather conditions
applicable to the route of flight and promotes a better understanding of weather informatio n. When
contacting Flight Service by phone, the FSS specialist will ask for the time and source of the previous
briefing, so the specialist does not inadvertently omit the necessary weather information.
3.3.1.3 Outlook Briefing
An outlook briefing may be requested when a planned departure is six or more hours away. It provides
initial forecast information that is limited in scope due to the timeframe of the planned flight. This type of
briefing is a good source of flight planning information that can influence decisions regarding route of
flight, altitude, and ultimately the “go, no-go” decision. A follow-up standard or abbreviated briefing prior
to departure is advisable, since an outlook briefing generally only contains information based on weather
trends and existing weather in geographical areas at or near the departure airport.
3.3.2 Telephone
3.3.2.1 Flight Service
For flights within the CONUS, Hawaii, and Puerto Rico, call 1 -800-WX-BRIEF (1-800-992-7433). For
flights in Alaska, call 1-833-AK-BRIEF (1-833-252-7433).
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Additionally, f or flights within Alaska , individual FSS telephone numbers are listed in the FAA Chart
Supplement for Alaska, Section 4, Associated Data.
FSS specialists are qualified and certified as Pilot Weather Briefers by the FAA. They are not authorized
to make original forecasts but are certified to translate and interpret available weather information directly
into terms describing the weather conditions that can be expected at the departure, along the route of flight,
and at the destination.
The FSS’ purpose is to serve the aviation community. Pilots can ask questions and discuss factors they do
not fully understand. The briefing is considered complete when the pilot has a clear picture of what weather
to expect.
3.3.2.2 Airport Weather
The latest weather reports from airport automated observing systems (e.g., AWOS and ASOS ) may be
accessed from the phone. Phone numbers can be found in FAA Chart Supplements.
3.3.3 Self-Briefing
Preflight decision making using online weather information continues to offer more options for the pilot.
The advent of interactive online aviation weather has allowed pilots to assemble aviation weather
information into a better decision-making process.
Pilots may receive a regulatory compliant briefing through online weather resources. Pilots that prefer to
contact an FSS are encouraged to use the online weather resources prior to calling. Some online weather
sources do not provide Flight Information Services (FIS), such as NOTAMs and temporary flight
restrictions (TFR). However, this information may also be found online through other websites. Another
example is the Alaska Aviation Weather Unit (AAWU) briefing tool for pilots in Alaska. This can be found
at https://www.weather.gov/aawu.
3.3.3.1 Flight Service 1800wxbrief.com
The FAA contract provider for flight services provides a website (https://www.1800wxbrief.com) that
allows pilots to review weather information, receive online preflight briefings, file flight plans, and receive
automatic notifications and alerts. The website also offers an interactive map to allow pilots to view a
variety of weather products and access to a variety of aeronautical information that can be tailored to their
planned flight route. See Chapter 28, Aviation Weather Tools, for additional information.
3.3.3.2 Aviation Weather Cameras
The FAA’s Aviation Weather Cameras website provides access to current weather camera images from the
FAA’s Aviation Weather Camera Network . On the website, pilots may compare the images to clear day
views or play back a loop of past images to establish weather trends. Weather camera images are a
supplementary product and may only be used to improve situational awareness.
The website also delivers a variety of safety of flight information including adverse conditions
(e.g., AIRMETs and SIGMETs), current conditions (e.g., Aviation Routine Weather Reports ( METAR),
radar, satellite imagery , and weather trends ), TAF s, PIREP s, and other aeronautical information
(e.g., remote communications outlets (RCO), TFRs, and charts).
The FAA’s Aviation Weather Cameras website can be found in Appendix G. The website uses a set of
progressive web application standards that enables an application -level experience on certain mobile
devices. See Section 24.9 for additional information.
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3.3.3.3 AviationWeather.gov
The website https://aviationweather.gov is operated by the NWS AWC in Kansas City, MO. It is a major
aviation weather website for obtaining text and graphical preflight weather information and products.
3.3.3.3.1 Graphical Forecasts for Aviation (GFA) Tool
The Graphical Forecasts for Aviation (GFA) Tool is a set of web-based displays that provide the necessary
aviation weather information to give users a complete picture of the weather that may impact flights in the
CONUS, Gulf of America, the Caribbean, portions of the Atlantic Ocean, and portions of the Pacific Ocean,
including the Hawaiian Islands and Alaska. See Chapter 28 for additional information.
3.3.3.4 Weather.gov
The National Digital Forecast Database (NDFD) is a suite of gridded forecasts of sensible weather elements
(e.g., cloud cover, maximum temperature). NWS field offices working in collaboration with the National
Centers for Environmental Prediction (NCEP) ar e combined in the NDFD to create a seamless mosaic of
digital forecasts. Weather elements necessary for aviation are included in the NDFD . However, be aware
that the NDFD may provide different forecast information for the same location and time than the GFA.
For further information about NDFD, please contact National Weather Service - Graphical Forecast
3.3.3.5 Flight Information Service-Broadcast (FIS-B)
Pilots can receive a regulatory compliant briefing through online weather resources that can be used in
conjunction with the Flight Information Service -Broadcast ( FIS-B) products. See Section 3.3.4.1 for
information on FIS-B.
3.3.3.6 Commercial Services
There are several commercial aviation weather providers that offer aviation weather and flight information
suitable for tablets and EFBs. These have a subscription fee for the service.
3.3.3.7 Weather Applications (Apps)
There are an increasing number of weather apps that allow pilots to access a wide range of weather reports
and forecasts from their phone, tablet, and computer. Some apps include flight planning services, in -flight
updates, NOTAMs, and TFRs. Details on these weather apps and other online weather services can be
found in the information from the service provider.
3.3.4 In-Flight Updates
3.3.4.1 Flight Information Service-Broadcast (FIS-B)
FIS-B over Universal Access Transceiver (UAT) datalink service provides aeronautical information and
meteorological i nformation to the flight deck for aircraft operating in the NAS. These products are
broadcast over the Automatic Dependent Surveillance -Broadcast (ADS-B) UAT link so that pilots have
timely information of regional weather and NAS status/changes that might affect flight. FIS-B aeronautical
information and meteorological information products provide strategic information to the flight deck that
enhances a preflight briefing. FIS-B products do not include all NOTAMs.
Advisory Circular ( AC) 00-63, Use of Flight Deck Displays of Digital Weather and Aeronautical
Information, contains detailed information concerning FIS-B meteorological products. The AIM Chapter 3,
Airspace; Chapter 4, Air Traffic Control; and Chapter 5, Air Traffic Procedures , contain information on
Special Use Airspace (SUA), TFR, and NOTAM products.
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FIS-B update intervals are defined as the rate at which the product data is available from the source.
Transmission intervals are defined as the amount of time within which a new or updated product
transmission must be completed and the rate or repetition interval at which the product is rebroadcast. Refer
to the AIM, Chapter 7, Section 1, Table 7 -1-3, FIS -B Over UAT Product Update and Transmission
Intervals, for update and transmission intervals for each FIS-B product.
Where applicable, FIS-B products include a look-ahead range expressed in nautical miles for three service
domains: Airport Surface, Terminal Airspace, and En Route/Gulf of America. The AIM, Chapter 7,
Section 1, Table 7-1-4, Product Parameters for Low/Medium/High Altitude Tier Radios , provides service
domain availability and look-ahead ranging for each FIS-B product.
Details on the content, format, and symbology of individual FIS -B products can be obtained from the
manufacturer of the avionics equipment used to receive and display them.
3.3.4.2 Automated Surface Observing System (ASOS) and Automated Weather Observing
System (AWOS)
ASOS and AWOS information can be retrieved in flight. Typically, the range of an ASOS/AWOS broadcast
is 25 NM. ASOS and AWOS frequencies are printed on Sectional Charts and listed in FAA Chart
Supplements. The majority of ASOS and AWOS are on airports, but there are a few located off -airport,
such as in a mountain pass. See Section 24.3 for more information on ASOS and AWOS.
3.3.4.3 Automatic Terminal Information Service (ATIS)
The Automatic Terminal Information Service ( ATIS) is a continuous broadcast on an assigned frequency
of recorded information in selected terminal areas to provide pilots with necessary airport and local area
information prior to arrival or departure.
ATIS frequencies can be found on Sectional Charts and Chart Supplement s, as well as on instrument
approach charts.
The ATIS broadcast is updated upon the receipt of new hourly weather, special weather, or when there is a
change in other pertinent data, such as runway change, instrument approach in use, etc.
3.3.4.4 Flight Service
FSS specialists provide in-flight weather updates as well as collect PIREPs. FSS frequencies are listed on
Sectional Charts and Chart Supplements.
3.3.4.5 Automatic Flight Information Service (AFIS) – Alaska Only
The Automatic Flight Information Service (AFIS) provides a continuous broadcast of recorded non-control
information at airports in Alaska where Flight Service provides local airport advisory (LAA) service. The
AFIS broadcast automates the repetitive transmission of essential but routine information, such as weather,
wind, altimeter, favored runway, b raking action, airport NOTAMs, and other applicable information. The
information is continuously broadcast over a discrete very high frequency (VHF) radio frequency (usually
the ASOS frequency). When rapidly changing conditions exist, the ceiling, visibility, altimeter, wind, or
other conditions may be omitted from the AFIS and will be issued by the FSS specialist on the appropriate
radio frequency. AFIS frequencies can be found on Sectional Charts and the Alaska Chart Supplement.
3.4 Overview of Aviation Weather Products
There are many aviation weather products available to the pilot through the internet and mobile phone apps.
Each product has a specific purpose that provides the user with reported or forecast weather conditions
either at an airport or aloft. Table 3-1 and Table 3-2 are matrices of aviation weather products versus the
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weather elements and the weather phenomena applicable to aviation. These tables are a high-level overview
and do not attempt to capture all products and elements.
A brief summary of the weather products that contain information pertaining to each weather element and
weather phenomen on is provided in individual tables in the next section. Technical specifications
(e.g., codes and contents) pertaining to the products in Table 3-1 and Table 3-2, as well as others, are
provided in Chapters 24, 25, 26, 27, and 28.
3.4.1 Weather Products versus Weather Elements and Phenomena
Table 3-1. High-Level Overview of Select Weather Products and Select Weather Elements and Phenomena that are
of Interest to Aviation Users (See Table 3-3 for acronyms and abbreviations.)
An ‘X’ indicates that the weather product contains information pertaining to the weather element or phenomenon.
Product T-
Storm Wind Wind
Shear Visibility Precip Fog In-Flight
Icing
Freezing
Level Turb Ash TC SS/
DS