NAME: __________________________
Date Due: ________________________
Chapter 2-4 Checkpoints: Weather Forecasting
Which service has provided weather forecasts to aviators since 1918?
The National Weather Service (p. 170)
What was the name of the act that Congress passed on 20 May 1926 and what did it do?
The Air Commerce Act
It directed the US Weather Bureau to make air travel safer. (p. 171)
List the four types of weather observations that meteorologists make.
1.
2.
3.
4.
Surface
Upper air
Radar
Satellite (p. 173)
The standard uniform altimeter setting is 29.92. At what altitude is this setting used and why?
Altimeters work by measuring the air pressure. When pilots take off and land, or pass over
mountains, they need to know the air pressure at that surface location. They then set their
altimeter to that pressure so that if the aircraft were on the ground, the altimeter would read
zero feet (this setting is called indicated altitude). This ensures the aircraft will have safe
distance above tall structures, hills, mountains, etc, and also where the ground is at take-off and
landing.
At cruising altitudes above 18,000 feet, all pilots set their altimeters with the standard uniform
altimeter setting of 29.92 (the “mean sea level” air pressure). Depending on the direction an
aircraft is cruising, they need to be at specific altitudes (for example, north flying aircraft may
be at 19,000 feet whereas south flying aircraft may be at 20,000 feet). The 29.92 altimeter
setting ensures all aircraft are using the same reference so they can fly at the correct altitudes
and avoid mid-air collisions.
What does each of the following weather devices measure?
Thermometer
Barometer
Altimeter
Psychrometer
Anemometer
------
Temperature
Air Pressure
Altitude
Relative Humidity
Wind Speed
What is ASOS? What are its limitations?
The Automated Surface Observing System (ASOS) is a weather reporting system that provides
surfaceobservations every minute via digitized voice broadcasts to aircraft using ground-to-air
radio. The system is a federally funded, joint program of the National Weather Service,
Federal Aviation Administration (FAA), and the Department of Defense. It serves as the
country’s main surface weather observing network. It works nonstop, 24 hours a day, every
day of the year. It’s particularly helpful to pilots when they are about to land. Besides the
computer-generated voice broadcasts, ASOS reports are also available in print and over the
phone.
ASOS has limitations. It can’t report any weather that takes place over the horizon. The
system’s sensors can only detect what’s directly overhead. It also isn’t able to report on any
event above 12,000 feet or phenomena such as tornadoes, freezing drizzle, or snow depth.
What are radiosondes and what data do they transmit?
Small instruments suspended from inflated weather balloons. They collect data such as air
temperature, pressure, wind speed, and wind direction as they rise to tens of thousands of feet.
They relay the data to ground stations via radio transmitters. When they reach more than
100,000 feet or so, the elastic balloons expand to their limits and pop. A parachute opens to
safely return the radiosondes to the ground.
How does a radar determine distance?
By measuring the time it takes—at the constant speed of light—for the radio wave to reach
an object and then return to the radar antenna. (p. 179)
List four types of radar. What is the role of each?
Doppler: Provides weather reports to local communities, forecasters, the military, and
airport weather observers, among others. Doppler radar rotates its antenna at different speeds
depending on the weather. Its two modes of operation are clear air and precipitation. Clear air
is air that contains small objects such as dust and other particulate matter. However, snow
doesn’t reflect radio waves very well, so the clear air mode is used to determine the presence of
light snow. When Doppler radar reads precipitation, such as rain, the antenna speeds
up to provide new images every four to six minutes.
FAA terminal Doppler: Found at major airports in the U.S. It also helps provide severe
weather alerts and warnings to air traffic controllers. It warns pilots about the presence of
wind shear, gust fronts, and heavy precipitation.
FAA airport surveillance: Main purpose is to detect aircraft. But air traffic controllers also
of precipitation so they can route air traffic around severe weather.
Aircraft airborne radar: Aircraft fly with airborne radar to find bad weather. This type of
radar can spot a big thunderstorm as well as detect light rainfall. It can also tell how big a
storm is.
What is the NEXRAD WSR-88D? How does it work?
It is the technical term for the Doppler radar network which is one of the most important
weather-tracking systems in the U. S. More than 160 Doppler radars scattered throughout the
US and overseas make up system. The maximum range of each radar is 250 nautical miles.
NEXRAD converts what the radars can read about a storm or other target—distance, strength,
and velocity—into images. These are the brightly colored maps you might see during
a TV weather report. The US departments of Commerce, Defense, and Transportation are
responsible for this massive system. The individual agencies within those departments that
oversee NEXRAD are the National Weather Service, Air Force, Navy, and the FAA. The heart
of the operation is the Radar Operations Center in Norman, Oklahoma.
What is the Geostationary Operational Environmental Satellite?
Several geostationary satellites orbit at a speed and altitude that keeps satellites in the same place
above the Earth at all times. They orbit about 22,300 miles above the equator. NOAA uses the
data collected by the GOES to forecast as well as observe ongoing weather such as
thunderstorms, tornadoes, fog, and flash floods, hurricanes, etc. The GOES can also spot
major events, including dust storms, volcanic eruptions, and forest fires. Each satellite can
observe a huge area. For instance, two satellites can cover North, Central, and South America
as well as the oceans surrounding them. Two types of satellite weather products are of
particular interest to pilots. They are Significant Meteorological Information (SIGMET) and
Airmen’s Meteorological Information (AIRMET) advisories.
Describe the following weather outlets for aviators.
Automated Flight Service Station: AFSS is the main source for preflight weather reports.
Pilots can get a preflight weather briefing from one of these stations 24 hours a day by
telephone. The service also offers in-flight weather data. The pilot will talk to a briefer at one of
these stations, who then tailors weather and other data depending on the pilot’s route, type of
aircraft, type of flight (visual flight rules or instrument flight rules), destination, and altitude.
Transcribed Information Briefing Service: Some, but not all, AFSSs offer this shortened
report called a TIBS. These briefings are prerecorded. They include special announcements.
They do not replace the fuller preflight briefings. They are simply meant to be a quick
rundown of weather and more.
En Route Flight Advisory Service: The EFAS is helpful once you’re in the air. This service
also goes by the name Flight Watch. Pilots must request this service to get timely in-fl ight
weather data tailored to their route, type of fl ight, and cruising altitude. An En Route
specialist can be one of the best sources for current weather along a route. This service is not
available 24 hours a day, however.
Hazardous Inflight Weather Advisory Service: HIWAS is a national program that broadcasts
bad weather alerts 24 hours a day. The broadcasts include reports such as SIGMETs and
AIRMETs. These broadcasts are only a summary. For a more in-depth report, pilots should
call an Automated Flight Service Station or En Route Flight Advisory Service specialist.
List and Describe the three types of weather briefings a pilot may ask for.
1. Standard Briefing. The most complete report. It provides an overall weather picture.
Pilots should get this type of briefi ng before departure and use it to plan a flight. It supplies
the following facts and more:
• Adverse conditions, including severe weather and airport closings
• A recommendation as to whether a pilot should fl y under visual flight rules
• An overview of the larger weather picture, such as fronts and major weather systems
• Current conditions, such as ceilings, visibility, winds, and temperatures
• En route weather forecast for the proposed fl ight route
• Destination forecast for the estimated time of arrival
• Winds and temperatures aloft for specifi c altitudes along the fl ight route
• Notices to Airmen, called NOTAMs, which include such things as airport closings and
restricted fl ight space (for example, Washington, DC); NOTAMs are published every 28 days.
2. Abbreviated Briefing. A shortened version of the standard briefing. Pilots should request
one when they’ve delayed their departure or need to update a previous briefing.
3. Outlook Briefing. Best when a departure isn’t planned for at least six hours. It helps
pilots plan a flight and can influence route, altitude, or even whether to scrap a flight altogether
if the weather promises to be bad enough.
Three typical current weather reports are: METARS, PIREPS, and RAREPs or SDs. What does each
acronym stand for and what does the report provide?
METARs: Aviation routine weather reports are hourly reports of current surface weather.
They include wind direction and speed, visibility, and the strength and location of weather from
precipitation to funnel clouds.
PIREPs: Pilot weather reports are reports on current upper air conditions that only pilots
can make. They include such things as icing.
RAREPs: Radar weather reports or storm detections (SDs). Provide current readings of
precipitation and thunderstorms by radar issued 35 minutes past the hour every hour.
Printed weather forecasts that pilots can read include TAFs, FAs, in-flight weather advisories, and
FDs. What does each acronym stand for and what does the report provide?
TAFs: Terminal aerodrome forecasts that cover a five-mile radius around airports.
FAs: Area forecasts give a picture of clouds, general weather, and visual conditions
expected over an area as large as several states.
In-Flight Weather Advisories SIGMETS: Significant Meteorological Information advisories
can cover areas of at least 3,000 square miles. They provide data about severe and extreme
turbulence, severe icing, and widespread dust or sandstorms that reduce what you can see to
less than three miles. These reports are useful to all kinds of aircraft.
In-Flight Weather Advisories AIRMETs: Airmen’s Meteorological Information advisories are
issued to modify earlier forecasts and reports. These are also useful to all aircraft. But they can
be especially vital to smaller aircraft with limited capabilities or to pilots with limited
experience. AIRMETs don’t cover severe weather events as SIGMETs do. Instead, they report
on less-severe weather such as moderate icing and moderate turbulence. They also look at
sustained surface winds of 30 knots or more, widespread areas of ceilings less than 1,000 feet,
and visibility of less than three miles.
FDs: Winds and temperatures aloft forecasts predict winds and temperatures for specific
spots based on upper air readings by radiosondes.
What types of data are provided on the following printed weather charts?
Surface Analysis Chart: A surface analysis chart assesses current surface weather
every three hours. These charts show areas of high and low pressure, fronts, temperatures,
dew points, wind directions and speeds, local weather, and visual obstructions. Symbols on the
chart indicate everything from the type of cloud to who made a particular weather observation.
Weather Depiction Chart: Another chart that lays out current surface conditions every three
hours. It updates the overall weather picture across the United States. It points out major
fronts, areas of high and low pressure, and visual flight rules versus instrument flight rules
weather.
Radar Summary Chart: Also looks at current weather (but not surface conditions). It’s a
collection of radar weather reports published every hour. It uses symbols to label type,
strength, and movement of a precipitation cell. It marks areas that are on severe weather
watch for tornadoes and severe thunderstorms with heavy dashed lines. If the radars aren’t
reading any kind of action, the chart will indicate this with an NA for not available. These
charts are for precipitation only. They do not show such things as clouds or fog.
Significant Weather Prognostic Chart: These charts forecast weather. They don’t report
current weather. They predict turbulence, freezing levels, and instrument flight rules weather.
They divide their forecasts into two readings. The first is for weather that could be found
between Earth’s surface and 24,000 feet, and the second for weather between 25,000 feet
and 60,000 feet.