Exam 4 – Review
**Exam 4 will be a multiple choice exam consisting of 35 questions
**Focus on definitions - (blue highlighted concepts in text)
**Focus on blue boxes - (important information given in these boxes)
Chapter 16 – Aviation Weather Resources
Section A: The Weather Forecasting Process
-
There are three important steps in the forecasting process: data collection, data
processing and forecasting
Collecting Weather Data
-
The World Meteorological Organization (WMO), a United Nations agency is
responsible for the standardization of observations and the international exchange
of weather data
Processing Weather Data
-
-
-
The National Weather Service (NWS), a part of the National Oceanic and
Atmospheric Administration (NOAA), is the U.S. government agency that is
primarily responsible for gathering and processing meteorological data and for
providing weather forecasts and warnings
These continuing and complicated tasks are conducted by several NWS offices
including the National Centers for Environmental Protection (NCEP) and local
Weather Forecast Offices (WFO)
One of the components of the NCEP is the Aviation Weather Center (AWC)
which specializes in the preparation of aviation weather information
Forecasting Methods
-
The most comprehensive forecast technique today is numerical weather prediction
(NWP) which solves a set of mathematical equations (a numerical model) to
predict the weather
Forecasting Accuracy
-
In comparison to persistence forecasts, the accuracy of meteorological forecasts,
which are based on scientific knowledge as used by NWP and weather
forecasters, is much better and decreases much more slowly as the forecast period
increases
-
-
-
However, for the longest forecast periods, the accuracy of meteorological
forecasts is no better than that of climatological forecasts, which are based purely
on past averages and are typically not very accurate at all
Forecasting the weather is somewhat chaotic, which is not too far from the mark.
As applied to weather forecasting, chaos theory describes the potential difficulty
in making forecasts for long periods of time
The science of chaos began in the early 1960s with a mathematician and
atmospheric scientist named Edward Lorenz and his exploration of computer
forecasts
Section B: Aviation Weather Forecast Products
-
Decoding keys for aviation weather forecast products are included in Appendix D
In addition, FAA Advisory Circular 00-45 Aviation Weather Services contains
further information
Selectivity – requires that you know exactly what you need, what is available and
where and when it is available
Visualization – forming a mental image of current and forecast weather
conditions
Forecast Products in Text Format
-
Forecast products in text format include:
Terminal Aerodrome Forecasts (TAF) – describes weather conditions
that are expected to occur within a 5 nm radius of an airport over a 24 hour
period. In the US routine TAFs are issued 4 times daily at 0000Z, 0600Z,
1200Z, and 1800Z. The TAF is one of the most valuable sources for the
predicted weather at a specific airport. Predicted sky condition, visibility,
weather and obstructions to vision, wind direction and speed, and expected
changes during the forecast period can be derived from TAFs.
Area Forecasts (FA) – expected VMC, clouds and general weather
conditions over an area the size of several states are described in an Area
Forecast (FA). An FA is used to determine enroute weather, including
conditions at airports that do not have terminal forecasts. An FA should
always be used in conjunction with the most recent inflight weather
advisories. Area forecasts are normally issued three times daily and are
valid for 18 hours. An FA has four sections:
1.
2.
Header – describes the source of the FA, the date and time of issue,
the valid times and the areas the FA covers
Precautionary Statements – describe IFR and mountain
obscurations, thunderstorm hazards, and states that all heights are
MSL unless otherwise noted
3.
4.
Synopsis – a brief summary identifying the location and movement
of pressure systems, fronts, and circulation patterns for the 18 hour
forecast period.
VFR Clouds and Weather – this section lists expected sky
condition, visibility and weather for the next 12 hours and an
outlook for the following 6 hours
- Area forecasts are issued by the Aviation Weather Center (AWC) for the six regions in
the contiguous US. The Alaskan Aviation Weather Unit issues an FA for the state of
Alaska while the Honolulu WFO handles Hawaii. Special FAs are also issued for the
Gulf of Mexico and international airspace
- Within its prescribed area, an FA describes weather features and conditions relative to
common geographical regions and features
- The contiguous US is divided into 6 forecast areas (SFO – San Francisco, SLC – Salt
Lake City, DFW – Dallas / Fort Worth, CHI – Chicago, BOS – Boston, MIA – Miami)
***The area forecast covers an area of several states and can be used to determine
en-route weather and conditions at your destination if no TAF has been issued
In-flight Weather Advisories (WS, WST, WA)
-
consist of either an observation and a forecast, or just a forecast for the
development of potentially hazardous weather
SIGMET (WS) – describes conditions which can pose hazards to all aircraft.
SIGMETs are valid for up to four hours.
If the following phenomena are observed or expected to occur, a SIGMET is
issued
1. Severe icing not associated with thunderstorms
2. Severe or extreme turbulence or clear air turbulence not associated with
thunderstorms
3. Dust storms or sandstorms lowering surface or inflight visibilities to below
three miles
4. Volcanic ash
***SIGMETs are issued as warnings of hazardous weather, such as severe icing,
which is of operational interest to all aircraft
-
Convective SIGMETs (WST) – describes convective activity that is potentially
hazardous to all categories of aircraft
Bulletins are issued hourly with special advisories issued as required
The forecast period for a WST is two hours or less
Criteria for issuance are any of the following conditions
1. Severe thunderstorms (surface winds greater than or equal to 50 knots and/or
hail at the surface greater than or equal to ¾ inches in diameter and/or
tornadoes)
-
-
-
2. Embedded thunderstorms
3. A line of thunderstorms
4. Thunderstorms producing precipitation with an intensity greater than or equal
to heavy and affecting 40% or more of an area at least 3,000 square miles
Convective SIGMET bulletins are issued for the Eastern (E), Central (C), and
Western (W) United States
Convective SIGMET text is presented in figure 16-7
AIRMET (WA) – issued for significant weather at intensities lower than those
required for the issuance of a SIGMET
Although AIRMETs are of operational interest to all aircraft, the weather
conditions specified are particularly hazardous to light aircraft having limited
capability or minimal equipment and instrumentation
There are three different AIRMETs
AIRMET Sierra – describes IFR conditions and/or extensive mountain
obscurations
AIRMET Tango – describes areas of moderate turbulence, sustained surface
winds in excess of 30 knots and areas of non-convective low-level wind shear
AIRMET Zulu – describes moderate icing and provides freezing level heights
Pilots with limited experience or qualifications should pay special attention to
these advisories
AIRMETs are issued every six hours with unscheduled updates and corrections
issued as necessary
Each bulletin contains any current AIRMETs that are in effect, an outlook for
weather that is expected after the AIRMET valid period and any significant
conditions that do not meet AIRMET criteria
Examples of AIRMETs Sierra, Tango and Zulu are given in figure 16-8
***Weather conditions that are particularly hazardous to small, single-engine
aircraft are contained in an AIRMET
-
AIRMETs and SIGMETs are issued for the 6 regions corresponding to the FA
areas
These widespread advisories must be either affecting or forecasted to affect at
least 3,000 square miles at any one time
International SIGMETs are issued worldwide by ICAO Meteorological Watch
Offices (MWOs); see figure 16-9
The criteria for International SIGMETs are broader than the criteria for either WS
or WST for the US
1.
Thunderstorms in lines, embedded in clouds, or in large areas
producing tornadoes or large hail
2.
Tropical cyclones
3.
Severe icing
4.
Severe or extreme turbulence
5.
Dust storms or sand storms lowering visibility to less than 3 miles
(5 km)
6.
Volcanic Ash
Transcribed Weather Broadcasts (TWEB)
-
A Transcribed Weather Broadcasts (TWEB) is a synopsis and forecast for a 50mile-wide corridor along a specific flight route or within 50 nm of the FSS
TWEBs are prepared for more than 200 flight routes and local vicinities around
the US
TWEB forecasts are valid for 12 hours
They are updated 4 times daily
TWEBs do not include areas of icing and turbulence
TWEB example given in figure 16-10
Winds and Temperatures Aloft Forecasts (FD)
-
-
FDs furnish a prediction of wind speed (knots), wind direction (degrees True),
and temperature (degrees C) for selected altitudes at specific locations across the
US, including Alaska, Hawaii and over some US coastal waters
Figure 16-11 gives the distribution of forecast stations
Winds and temperatures aloft contain wind direction in relation to true north,
wind speed in knots and temperature in degrees Celsius for a range of altitudes
FDs wind speeds between 100 and 199 knots are encoded so direction and speed
can be represented by four digits
These winds are decoded by subtracting 50 from the two digit wind direction and
adding 100 to the wind speed
The negative sign for temperatures above 24,000 feet MSL is not included
A wind code of 9900 is interpreted as light and variable
Forecast winds greater than or equal to 199 knots are reported as 199 knots
Other Advisories, Watches, and Warnings
-
-
Center Weather Service Unit (CWSU) – operated by NWS meteorologists within
the confines of each ARTCC
Meteorological impact statements (MIS) / center weather advisories (CWA) –
produced by the CWSU of each ARTCC
Hurricane advisories (WH) – issued to alert the aviation community to the
presence of a hurricane located at least 300 nm offshore and threatening the
coastline
Severe watch bulletin (WW) – an unscheduled message that defines areas of
possible severe thunderstorms or tornado activity
Severe watch alert (AWW) – a preliminary notice to alert forecasters, briefers and
pilots that WW is being issued
Severe thunderstorm warnings / tornado warnings – public notifications that those
phenomena have been sighted visually or by radar
Convective outlook (AC) – SPC also produces a convective outlook (AC) for the
occurrence of thunderstorms (non-severe and severe) five times a day for the next
24 hours (day 1 convective outlook) and twice a day for the following 24 hours
(day 2 convective outlook)
Forecast Products in Graphic Format
-
Descriptions of examples of all common forecast and analysis graphics are given
in Appendix D
Significant Weather Prognostic Chart
-
-
-
The significant weather prognostic chart can be used to determine areas to
avoid, such as forecast locations of low visibilities or turbulence
See figure 16-13
Lower left hand corner of each panel gives the valid times for the forecast
The surface prog in the lower panel uses standard symbols to depict fronts,
isobars, pressure centers and areas of forecast precipitation
Regions of continuous precipitation and unstable showery precipitation are within
a solid green line with hatching
Intermittent precipitation is only enclosed with a solid green line
The upper panel portrays forecast areas of IFR (solid red lines)
MVFR (scalloped green lines)
VFR conditions
Areas and layers of expected moderate or greater turbulence are enclosed with
dashed yellow lines
The highest freezing level (dashed green lines) and the intersection of the freezing
level with the surface are also shown
High-level significant weather prog chart – covers the airspace from 25,000
feet to 60,000 feet pressure altitude
Charts from some world area forecast centers (WAFC) cover the layer from
FL240 to FL630
A wide range of information can be interpreted from this chart including forecast
of thunderstorm areas, tropical cyclones, surface positions of well-defined
convergence zones, movement of frontal systems and the locations and speeds of
jetstreams; see figure 16-14
The positions of jet streams with speeds greater than 80 knots are indicated by
long, heavy lines with arrowheads showing the direction of flow
Each jet is labeled with altitude; speed and direction of the maximum wind in the
jet core is shown with conventional wind barbs
Heights of the tropopause are indicated in boxes; relatively high and low
tropopause heights are indicated with H and L respectively
Areas of significant CB (thunderstorm) activity are enclosed in scallooed lines
with heights of tops and bases indicated
If the base of the layer is below 25,000 feet it is indicated by xxx
These areas include CB embedded in clouds, haze, or dust
Areas of moderate and greater turbulence are enclosed in dashed lines
-
Predicted intensities and heights of bases and tops of the turbulent layers are also
given
The high-level significant weather prog chart also includes positions of surface
fronts, squall lines and the location of volcanic eruptions; see Appendix D for
more details
Forecast Winds and Temperatures Aloft Chart
-
The third forecast graphic that is useful for flight planning is the forecast winds
and temperatures aloft chart
This is simply a graphical presentation of the information given in FD forecast
bulletins
See figure 16-15 for a sample FD chart for international flights
Wind and temperature predictions are produced at regularly spaced latitude and
longitude positions on international charts
Other useful forecast charts include the convective outlook chart and the volcanic
ash forecast transport and dispersion (VAFTAD) chart
Section C: Aviation Weather Information Sources
FAA Flight Service Stations (FSS)
-
-
The flight service station (FSS) is one of the most common sources of weather
information for pilots
Automated flight service stations (AFSS) – about one per state; these are the
result of consolidating older, manual stations
More aviation weather briefing services are provided by FAA flight service
stations than any other government service
The most common method of obtaining weather information from an FSS is a
briefing over the telephone
You can obtain one of three types of briefings: standard, abbreviated and outlook
An FSS briefing can be obtained by dialing 1-800-WX-BRIEF
A standard briefing – provides you with the most complete weather picture
tailored to your specific flight; figure 16-16 lists the items included in a standard
briefing
For a telephone briefing it is helpful to have examined these data ahead of time
An abbreviated briefing – enables you to supplement mass disseminated data,
update a previous briefing, or request specific information
If your proposed departure time is six or more hours in the future an outlook
briefing provides a general overview of forecasted weather
***You should request a standard briefing if you have received no preliminary
weather information and are departing within the hour. To supplement mass
disseminated data, an abbreviated briefing should be requested. The FSS provides
an outlook briefing 6 or more hours in advance of your proposed departure time
-
-
Transcribed information briefing service (TIBS) – an AFSS service that provides
continuous telephone recordings of meteorological and/or aeronautical
information 24 hours a day
TIBS provides route briefings and depending on user demand aviation weather
observations, forecasts and wind and temperature aloft forecasts
TIBS information is frequently updated to ensure current and accurate weather
data
Local numbers for TIBS are available in the AFD (Airport Facility Directory)
En route flight advisory service (EFAS) – probably the most familiar inflight
service to pilots
To use this service contact the specific EFAS by using the words “Flight Watch”
The frequency for flight watch below 18,000 feet MSL is 122.0 MHz
Upon your request, the flight watch specialist can provide aviation weather
information and time-critical enroute assistance
If you are facing hazardous or unknown weather conditions, EFAS may
recommend alternate or diversionary routes
The receipt and rapid dissemination of pilot weather reports is a primary
responsibility of EFAS
***At altitudes below 18,000 feet, you can contact Flight Watch on 122.0 MHz for
information regarding current weather along your proposed route of flight
Continuous Broadcasts of Weather Information (TWEB, HIWAS)
-
TWEB is aired continuously over selected low and medium frequency NDBs
(nondirectional beacons), on 190 – 535 kHz and over VORs (very high frequency
omni-directional ranges) on 108.0 – 117.95 MHz
***TWEBs contain in-flight cross-country weather information including winds
and temperatures aloft forecasts
-
Hazardous inflight weather advisory service (HIWAS) – another in-flight service
that provides a continuous broadcast over selected VORs to inform you of
hazardous flying conditions such as turbulence, icing, IFR conditions and high
winds
Other Weather Information Sources
-
Automatic terminal information service (ATIS) – available at most major airports
that have operational control towers
ATIS is a pre-recorded report, broadcast on a dedicated frequency which includes
information regarding current weather and pertinent local airport conditions
ATIS is normally recorded every hour but may be updated any time
ATIS frequencies are listed in the AFD (Airport Facility Directory)
Direct user access terminal service (DUATS) – The FAA supports the DUATS
service
-
This computer-based program provides NWS and FAA products that are normally
used in pilot weather briefings
By using a personal computer and modem you can access weather information
prior to flight
Flight plans can also be filed and amended through DUATS
Other weather sources include weather forecasts by local news broadcasts, the
Weather Channel, airing on cable television and Jeppesen DataPlan
Weather on the Internet
-
The internet is probably one of the fastest growing sources of aviation weather
Appendix F gives a large number of US and international agencies that provide
both aviation weather information and general weather information
Chapter 17 – Weather Evaluation for Flight
Section A: Self – Briefing Procedure
-
To improve your proficiency in weather evaluation, the development of a system
for processing information during flight planning is valuable
A flow diagram outlining this process is shown in figure 17-1
1. Weather Awareness
2. Knowledge of available and relevant weather products
3. Self evaluation
4. Aircraft Capability
5. Flight description
6. Weather Overview
7. Preflight Weather Evaluation (cancel, go, delay)
8. In-flight Weather Evaluation
9. No change – proceed to destination
10. Divert – Alternate
-
Is your meteorological training adequate?
Are you familiar with relevant weather products and their sources?
Self Evaluation
-
Are you current to flying in the weather conditions of the proposed flight?
Is your weather knowledge current
Are you up-to-date on the latest weather resources?
Aircraft Capability
-
A complete understanding of your aircraft’s performance capability and
limitations is essential in evaluating the weather’s impact
The equipment onboard your aircraft is another factor to consider when assessing
aircraft capabilities
Based on a complete assessment of yourself and your aircraft you can set specific
weather restrictions for your flights
Flight Description
-
The next step in the self-briefing process is to establish a complete flight
description
Figure 17-2; a flight plan form can be used as a reference for the flight description
items supplied to a briefer
***When you request a briefing, identify yourself as a pilot and supply the briefer
with the following information: type of flight planned (VFR or IFR), aircraft
number or pilot’s name, aircraft type, departure airport, route of flight, destination,
flight altitude(s), estimated time of departure and estimated time en-route or
estimated time of arrival
Section B: Weather Evaluation Process
-
Once the initial steps of the self-briefing procedure are complete, the analysis of
weather for a specific flight can begin
Your misinterpretation of a critical piece of weather information is a pilot error
Misinterpretations of weather observations and forecasts are usually due to not
knowing one or more of the following:
1.
2.
3.
4.
What is available
What the information means
Where you can get it
When it is available
Overview
-
-
It is worthwhile to begin assessing the general weather situation a day or two
before the flight
Pay attention to weather reports and forecasts on radio and television
As time goes on, details should be added to the general patterns
The Internet or an FSS outlook briefing is helpful at this point
About 24 hours in advance of your departure, ask yourself these questions:
1. Where are the areas of potentially adverse weather currently located?
2. How have those areas been moving/developing in the last 24 hours or so?
3. Where will those areas be at the time of your flight?
4. What are the specific flight hazards?
Refer to the surface analysis charts
In many weather situations, the intensity and organization of the weather system
becomes clearer when you examine upper air conditions
Refer to constant pressure analysis charts
Refer to low-level significant weather prognostic charts
Your efficient use of weather information requires that you determine all of the
weather hazards significant to your flight
An outlook briefing from flight service furnishes additional information at this
stage
Preflight Evaluation
-
-
The preflight weather evaluation is usually accomplished within a few hours of
the proposed departure time due to the importance of procuring the latest
information prior to the flight
Graphic weather material makes it much easier and faster to visualize the weather
situation
-
-
This includes satellite images and maps of various weather phenomena
Plotted in-flight weather advisories and maps showing recent PIREPs are
particularly useful
One of your important tasks at this stage is to make use of all advisories or
warnings issued for the area at the time of your flight; look at area forecast,
AIRMETS - Sierra, Tango, Zulu, SIGMETS, CONVECTIVE SIGMETS, surface
analysis charts, weather depiction charts
To conclude the weather evaluation, you must make a decision based on your
analysis
An important component of the self-briefing procedure is your own weather
observation
In-Flight Evaluation
-
Your evaluation of the weather does not end if a go decision is made
The dynamic nature of weather makes in-flight weather evaluation essential to
safety
While en-route you should also use in-flight weather services such as recorded
surface observations and forecasts (TWEB, HIWAS)
Figure 17-16; Flight Watch is a valuable weather service provided by flight
service stations
Section C: Developments in Aviation Weather Resources
-
The worldwide aviation community is making major changes in the way weather
data are gathered, processed and disseminated
In the US, the FAA and the National Weather Service are implementing plans
leading to an advanced and improved aviation weather system
This system will integrate present and pending technologies to develop higher
resolution and more accurate observations of atmospheric variables
Increased computer power and modeling capabilities will significantly enhance
weather analyses and forecasts
Weather information will be transformed into aviation decision aids based on
weather variables impacting flight
Observation Systems
-
The focus of modernized weather observation is the production of high-quality
data in nearly real time
It is expected that there will be 1,500 automated surface-observation stations such
as ASOS and AWOS
The Doppler weather radar (WSR-88D) was deployed initially as NEXRAD and
is now the primary tool of the US weather radar network
Terminal Doppler weather radar (TDWR) has been installed at numerous large
airports in the US where thunderstorms and microbursts are most common
-
-
-
-
Low-level wind shear alert systems (LLWAS) have been installed at 110 airports
in the US
The radiosonde network has been the primary upper-air data source for weather
forecasting for many years
The wind profiler is a vertically pointing microwave radar that measures
horizontal wind speed and direction at 72 levels between about 1,500 feet AGL
and 53,000 feet MSL
Another on-going development in upper-air observations has been the
development of the international aircraft meteorological data reporting (AMDAR)
system using commercial aircraft as observational platforms
There are two primary data-gathering systems by AMDAR
The first is the aircraft-to-satellite data relay (ASDAR) system which uses
specially designed hardware that must be fitted to and certified for the aircraft on
which it is installed
The second method for the gathering of meteorological information from aircraft
is the aircraft communications, addressing and reporting system (ACARS)
The AMDAR (ASDAR/ACARS) system has been highly successful
The modern weather satellite has developed far beyond the acquisition of images
of cloud patterns
Satellites such as the geostationary operational environmental satellite (GOES)
provide simultaneous imaging as well as temperature and moisture profiles
Weather Forecasting
-
-
-
-
In addition to more and better meteorological observations, a better understanding
of atmospheric processes, faster computers, and better numerical techniques are
leading to significant improvements in weather forecasting
A strong US government initiative in support of aviation has resulted in the
development of the aviation gridded forecast system (AGFS)
The purpose of AGFS is to use the output from NCEP models, such as RUC and
other specialized computer code to generate high resolution Aviation Impact
Variables (AIV)
The Aviation Division of the NOAA Forecast Systems Laboratory works
cooperatively with the Aviation Weather Center (AWC) to integrate AIVs into the
aviation forecast process
Other on-going efforts to improve aviation weather forecasts are aimed at
thunderstorms, ceiling and visibility predictions, ground deicing, and the
prediction of wake vortex behavior at air terminals
Weather Information Systems
-
Effective aviation weather information systems must meet two important
requirements
The world area forecast system (WAFS) is a satellite communications system to
provide the worldwide aviation community with weather information for flight
planning and to support the en-route phase of flight
-
-
-
In the US, the FAA’s Aviation Weather Research (AWR) program supports a
research project that is addressing the need for improved weather presentation
Two other significant components of the AWR program are the aviation weather
products generator (AWPG) and the integrated terminal weather system (ITWS)
The purpose of the AWPG is to provide analysis and forecast products tailored for
the en-route phase of flight
ITWS is designed to enhance the FAA’s ability to monitor and predict weather
that impacts aircraft in the vicinity of the terminal
Input into ITWS includes LLWAS, weather radar, automated weather
observations, aircraft observations and forecast model output
By 1999, ITWS had been deployed to 34 locations serving 45 of the busiest
airports in the US
In the future, the weather requirements for free flight and other planned
improvements to the national and global air navigation systems will make rapid
delivery of better weather information to the cockpit a priority
Beyond TWIP, the FAA is developing standards and procedures for the
transmission of enhanced weather information directly to the cockpits of aircraft
in all phases of flight
As these cockpit request/display systems become a reality, concern for simplicity
in operation and interpretation will be critical in order to reap the maximum safety
benefits in an already busy cockpit