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67 Cards in this Set

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A. Nature of the Atmosphere
1. State the general characteristics in regard to the flow of air around high and low pressure systems in the Northern Hemisphere.
Low Pressure - inward, upward, and counterclockwise

High Pressure - outward, downward, and clockwise
AC 00-6A
A. Nature of the Atmosphere
2. What is a "trough"?
A trough (also called a trough line) is an elongated area of relatively low atmospheric pressure. At the surface when air converges into a low, it cannot go outward against the pressure gradient, nor can it go downward into the ground; it must go upward. Therefore, a low or trough is an area of rising air. Rising air is conducive to cloudiness and precipitation; hence the general association of low pressure and bad weather.
AC 00-6A
A. Nature of the Atmosphere
3. What is a "ridge"?
A ridge (also called a ridge line) is an elongated area of relatively high atmospheric pressure. Air moving out of a high or ridge depletes the quantity of air; therefore, these are areas of descending air. Descending air favors dissipation of cloudiness; hence the association of high pressure and good weather.
AC 00-6A
A. Nature of the Atmosphere
4. What are the standard temperature and pressure values for sea level?
15 degrees C and 29.92" Hg
AC 00-6A
A. Nature of the Atmosphere
5. What are "isobars"?
An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure.
AC 00-6A
A. Nature of the Atmosphere
6. If the isobars are relatively close together on a surface weather chart or a constant pressure chart, what information will this provide?
The spacing of isobars on these charts defines how steep or shallow a pressure gradient is. When isobars are spaced very close together, a steep pressure gradient exists which indicates higher wind speeds. A shallow pressure gradient (isobars not so close together) usually means wind speeds will be less.
AC 00-6A
A. Nature of the Atmosphere
7. What causes the winds aloft to flow parallel to the isobars?
The Coriolis force.
AC 00-6A
A. Nature of the Atmosphere
8. Why do surface winds generally flow across the isobars at an angle?
Surface friction.
AC 00-6A
A. Nature of the Atmosphere
9. At what rate does atmospheric pressure decrease with an increase in altitude?
1" Hg per 1000 feet.
AC 00-6A
A. Nature of the Atmosphere
10. What does "dew point" mean?
Dew point is the temperature to which a sample of air must be cooled to attain a state of saturation.
AC 00-6A
A. Nature of the Atmosphere
11. When temperature and dew point are close together (within 5 degrees), what type of weather is likely?
Visible moisture in the form of clouds, dew, or fog. Also, these are ideal conditions for carburetor icing.
AC 00-6A
A. Nature of the Atmosphere
12. What factor primarily determines the type and vertical extent of clouds?
The stability of the atmosphere.
AC 00-6A
A. Nature of the Atmosphere
13. How do you determine the stability of the atmosphere?
By observing the actual lapse rate and comparing it to the standard lapse rate of 3.5 F per 1,000 feet. The "K" index of a stability chart is the primary means of determining stability. In general, stable air cools at a rate less that the standard lapse rate with altitude, and unstable air cools at a rate that is greater than the standard lapse rate.
AC 00-6A
A. Nature of the Atmosphere
14. List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility.
Category: Stable / Unstable
Clouds: Stratiform / Cumuliform
Turbulence: Smooth / Rough
Precipitation: Steady / Showery
Visibility: Fair to Poor / Good
AC 00-6A
A. Nature of the Atmosphere
15. At what altitude above the surface would the pilot expect the bases of cumuliform clouds if the surface temperature is 82 and the dewpoint is 62?
You can estimate the height of cumuliform cloud bases using surface temperature/dewpoint spread. Unsaturated air in a convective current cools at about 5.4F (3.0C) per 1,000 feet; dew point decreases at about 1F (5/9C). Thus, in a convective current, temperature and dew point converge at about 4.4F (2.5C) per 1,000 feet. You can get a quick estimate of a convetive cloud base in thousands of feet by rounding the values and dividing into the spread. When using Fahrenheit, divide by 4 and multiply by 1,000. This method of estimating is reliable only with instability, clouds and during the warmer part of the day.

((Temp-DewPoint)/4)*1,000 = Base of Clouds

((82-62)/4)*1000 = 5,000 AGL
AC 00-6A
A. Nature of the Atmosphere
16. What will the freezing level be if the field elevation is 1,000 feet and the temperature at the surface is 15C?
The freezing level (0C) can be estimated by subtracting 2C per 1,000 feet (average lapse rate) from 15C and then adding the result to the field elevation. For this example the freezing level will be at 8,500 MSL.
AC 00-6A
A. Nature of the Atmosphere
17. What conditions are necessary for structural icing to occur?
Visible moisture and below freezing temperatures at the point moisture strikes the aircraft.
AC 00-6A
A. Nature of the Atmosphere
18. What are the two main types of icing?
Structural and induction.
AC 00-6A
A. Nature of the Atmosphere
19. Name four types of structural ice.
Clear ice - forms when large drops strike the aircraft surface and slowly freeze.

Rime ice - small drops strike the aircraft and freeze rapidly.

Mixed ice - combination of above; supercooled water drops varying in size.

Frost - ice crystal deposits formed by sublimation when temperature and dew point are below freezing.
AC 00-6A
A. Nature of the Atmosphere
20. What action is recommended if you inadvertently encounter icing conditions?
Change course and/or altitude; usually, climb to a higher, if possible.
AC 00-6A
A. Nature of the Atmosphere
21. Is frost considered to be hazardous to flight? Why?
Yes, because while frost does not change the basic aerodynamic shape of the wing, the roughness of its surface spoils the smooth flow of air, thus causing a slowing of the airflow. This slowing of the air causes early airflow separation, resulting in a loss of lift. Even a small amount of frost on airfoils may prevent an aircraft from becoming airborne at normal takeoff speed. It is also possible that, once airborne, an aircraft could have insufficient margin of airspeed above stall so that moderate gusts or turning flight could produce incipient or complete stalling.
AC 00-6A
A. Nature of the Atmosphere
22. What factors must be present for a thunderstorm to form?
a. A source of lift (heating, fast-moving front)
b. Unstable air (nonstandard lapse rate)
c. High moisture content (temperature/dew point close)
AC 00-6A
A. Nature of the Atmosphere
23. What are the three stages of a thunderstorm?
Cumulus stage - Updrafts cause raindrops to increase in size.

Mature stage - Rain at earth's surface; it falls through or immediately beside the updrafts; lightning; perhaps roll clouds.

Dissipating stage - Downdrafts and rain begin to dissipate.
AC 00-6A
A. Nature of the Atmosphere
24. What is a "temperature inversion"?
An inversion is an increase in temperature with height - a reversal of the normal decrease with height. An inversion aloft permits warm air to fall through cold air below. Temperature in the cold air can be critical to icing. A ground-based inversion favors poor visibility by trapping fog, smoke, and other restrictions into low levels of the atmosphere. The ais is stable, with little or no turbulance.
AC 00-6A
A. Nature of the Atmosphere
25. State two basic ways that fog may form.
a. Cool air to the dew point.
b. Adding moisture to the air.
AC 00-6A
A. Nature of the Atmosphere
26. Name several types of fog.
a. Radiation fog
b. Advection fog
c. Upslope fog
d. Precipitation-induced fog
e. Ice fog
AC 00-6A
A. Nature of the Atmosphere
27. What causes radiation fog?
The ground cools the adjacent air to the dew point on calm, clear nights.
AC 00-6A
A. Nature of the Atmosphere
28. What is advection fog, and where is it most likely to form?
Advection fog results from the transport of warm humid air over a cold surface. A pilot can expect advection fog to form primarily along coastal areas during the winter. Unlike radiation fog, it may occur with winds, cloudy skies, over a wide geographic area, and at any time of the day or night.
AC 00-6A
A. Nature of the Atmosphere
29. What is upslope fog?
Upslope fog forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. Once the upslope wind ceases, the fog dissapates. Upslope fog is often quite dense and extends to high altitudes.
AC 00-6A
A. Nature of the Atmosphere
30. Define the term "wind shear," and state the areas in which it is likely to occur.
Wind shear is defined as the rate of change of wind velocity (direction and/or speed) per unit distance; conventionally expressed as vertical or horizontal wind shear. It may occur at any level in the atmosphere but three areas are of special concern:
a. Wind shear with a low-level temperature inversion.
b. WInd shear wiin a frontal zone or thunderstorm.
c. Clear air turbulance (CAT) at high levels associated with a jet stream or strong circulation.
AC 00-6A
A. Nature of the Atmosphere
31. Why is wind shear an operational concern to pilots?
Wind shear is an operational concern because unexpected changes in wind speed and direction can be potentially very hazardous to aircraft operations at low altitudes on approach to and departing from airports.
AC 00-6A
B. Obtaining Weather Information
1. What is the primary means of obtaining a weather briefing?
The primary source is an individual briefing obtained from a briefer at the AFSS/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).
AIM 7-1-2
B. Obtaining Weather Information
2. What are some examples of other sources of weather information?
a. Telephone Information Briefing Service (TIBS) (AFSS)
b. Transcribed Weather Broadcasts (TWEB)
c. Telephone Access to TWEB (TEL-TWEB)
d. Weather and aeronautical information from numerours private industry sources
e. The direct User Access System (DUATS)
AIM 7-1-2
B. Obtaining Weather Information
3. Where can you find a listing of FSS and weather information numbers?
Numbers for these services can be found in the Airport/Facility Directory under the "FAA and NWS Telephone Numbers" section. They are also listed in the U.S. Government section of the local telephone directory.
AIM 7-1-2
B. Obtaining Weather Information
4. What types of weather briefings are available from an FSS briefer?
Standard Briefing - Request when you are planning a flight and you have not received a previous briefing or have not received preliminary information through mass dissemination media (TIBS, TWEB, etc.).

Abbreviated Briefing - Request when you need information to supplement mass disseminated data, update a previous briefing, or when you need only one or two items.

Outlook Briefing - Request whenever your proposed time of departure is six or more hours from the time of the briefing; for planning purposes only.

Inflight Briefing - Request when needed to update a preflight briefing.
AIM 7-1-4
B. Obtaining Weather Information
5. What pertinent information should a weather briefing include?
a. Adverse Conditions
b. VFR Floght Not Recommended
c. Synopsis
d. Current Conditions
e. Enroute Forecast
f. Destination Forecast
g. Winds Aloft
h. Notices to Airmen (NOTAMs)
i. ATC Delay
j. Pilots may obtain the following from AFSS/FSS briefers upon request: Information on MTRs and MOAs, a review of printed NOTAM publications, approximate density altitude information, information on air traffic services and rules, customs/immigration procedures, ADIZ rules, search and rescue, LORAN, NOTAM, GPS RAIM availability, and other assistance as required.
AIM 7-1-4
B. Obtaining Weather Information
6. What is EFAS?
En route Flight Advisory Service (EFAS) is a service specifically designed to provide enroute aircraft with timely and meaningful weather advisories pertinent to the type of flight intended, route of flight, and altitude. In conjunction with this service, EFAS is also a central collection and distribution point for pilot reported weather information (PIREPs). EFAS provides communications capabilities for aircraft flying at 5,000 feet AGL to 17,500 feet MSL on a common frequency of 122.0 MHz. It is also known as "Flight Watch."
AIM 7-1-5
B. Obtaining Weather Information
7. What is HIWAS?
Hazardous In-flight Weather Advisory Service (HIWAS) is a continuous broadcast of in-flight weather advisories including summarized Aviation Weather Warnings, SIGMETs, Convective SIGMETs, Center Weather Advisories, AIRMETs, and urgent PIREPs. HIWAS is an additional source of hazardous weather information which makes this data available on a continuous basis.
AIM 7-1-10
C. Aviation Weather Reports and Observations
1. What is a METAR?
METAR, or Aviation Routine Weather Report: An hourly surface observation of conditions observed at an airport.
AC 00-45E
C. Aviation Weather Reports and Observations
2. Describe the basic elements of a METAR?
A METAR report contains the following elements in order as presented:
a. Type of report - the METAR, and the SPECI (aviation special weather report).
b. ICAO station identifier - 4-letter station identifiers; in the conterminous U.S., the 3-letter identifier is prefixed with a K.
c. Date and time of report - a 6-digit date/time group appended with Z (UTC). First two digits are the date, then two for the hour, and two for the minutes.
d. Modifier (as required) - if used, the modifier AUTO identifies the report as an automated weather report with no human intervention. If AUTO is shown in the body of the report, A01 or A02 will be encoded in the remarks section to indicate the type of precipitation sensor used at the station.
e. Wind - 5-digit group (5 digits if speed is over 99 knots); first three digits = wind direction, in tens of degrees referenced to true north. Directions less than 100 degrees are preceded with a zero; next two digits are the average speed in knots, measured or estimated (or, if over 99 knots, the next three digits).
f. Visibility: prevailing visibility - statue miles, space, fractions of statue miles (as needed), and the letters SM.
g. Runway visual range (RVR), as required.
h. Weather phenomena - broken into two categories: qualifies, and weather phenomena.
i. Sky conditions - amount/height/type (as required) or indefinite ceiling/height (vertical visibility).
j. Temperature/dew point group - 2-digit format in whole degrees Celsius, separated by a solidus (/). Temperatures below zero are prefixed with M.
k. Altimeter - 4-digit format representing tens, units, tenths, and hundredths of inches of mercury prefixed with A. The decimal point is not reported or stated.
l. Remarks (RMK), as required - operational significant weather phenomena, location of phenomena, beginning and ending times, direction of movement.

Example:
METAR KLAX 140651Z AUTO 00000KT 1SM R35L/4500V6000FT -RA BR BKN030 10/10 A2990 RMK A02
AC 00-45E
C. Aviation Weather Reports and Observations
3. Describe several types of weather observing programs available.
a. Manual Observations - reports made from airport locations staffed by FAA or NWS personnel.
b. AWOS - Automated Weather Observing System; consists of various sensors, a processor, a computer-generated voice subsystem, and a transmitter to broadcast local, minute by minute weather data directly to the pilot. Observations will include the prefix AUTO in the data.
c. AWOS Broadcasts - computer-generated voice is used to automate the broadcast of minute-by-minute weather observations.
d. ASOS - Automated Surface Observing System; the primary U.S. surface weather observing system. Up to 993 systems installed throughout the U.S. providing minute-by-minute observations generating METARs and other aviation weather information. Transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID. ASOS includes the prefix "AUTO" in the reported data.
AIM 7-1-12
C. Aviation Weather Reports and Observations
4. What are PIREPs (UA), and where are they usually found?
These reports contain information concerning weather observed by pilots en route. Required elements for all PIREPs are message type, location, time (in UTC), flight level (altitudes are MSL), type of aircraft, and a least one weather element encountered (visibility in SM, distance in NM). A PIREP (abbreviation for "pilot reports") is usually transmitted as an individual report but can be appended to a surface aviation weather report or placed into collectives. Also referred to in coded reports as "UA."
AC 00-45E
C. Aviation Weather Reports and Observations
5. What are Radar Weather Reports (SD)?
General areas of precipitation, including rain, snow, and thunderstorms, can be observed by radar. The radar weather report (SD) includes the type, intensity, and location of the echo top of the precipitation. All heights are reported above MSL. Radar stations report each hour at H+35. SDs should be used along with METARs, satellite photos, and forecasts when planning a flight, to help in thunderstorm area avoidance. Once airborne, depend on Flight Watch, which has the capability to display current radar images, airborne radar, or visual sighting to evade individual storms.
AC 00-45E
D. Aviation Weather Forecasts
1. What are Terminal Aerodrome Forecasts (TAFs)?
An Aviation Terminal Forecast (TAF) is a concise statement of the expected meteorological conditions within a 5-SM radius from the center of an airport's runway complex during a 24-hour time period. The TAFs use the same weather code found in METAR weather reports, in the following format:
a. Type of report - a routine forecast (TAF); and an amended forecast (TAF AMD).
b. ICAO station identifier - 4-letter station identifiers.
c. Date and time of origin - the date and UTC the forecast actually prepared; 2-digit date, and 4-digit time, (no space), followed by the letter Z.
d. Valid period date and time - valid forecast period is a 2-digit date followed by the 2-digit beginning and 2-digit ending hours in UTC. Routine TAFs are valid for 24 hours and are issued four time daily at 0000Z, 0600Z, 1200Z, and 1800Z.
e. Forecasts - wind, significant weather, sky conditions, non-convective low-level wind shear, change indicators, probability.
AC 00-45E
D. Aviation Weather Forecasts
2. What is an Aviation Area Forecast (FA)?
A forecast of visual meteorological conditions (VMC), clouds, and general weather conditions over an area the size of several states. To understand the complete weather picture, the FA must be used along with inflight weather advisories to determine forecast enroute weather and to interpolate conditions at airports where no TAFs are issued. FAs are issued 3 times a day by the Aviation Weather Center (AWC) for each of the 6 areas in the contiguous 48 states. The weather forecast office (WFO) in Honolulu issues FAs for Hawaii. The Alaska Aviation Weather Unit (AAWU) in Anchorage, Alaska produces the FA for the entire state of Alaska. There are also two specialized FAs, one for the Gulf of Mexico, and one for international airspace.
AC 00-45E
D. Aviation Weather Forecasts
3. What information is provided by an Aviation Area Forecast (FA)?
The FA is comprised of four sections:
a. Communications and product header section - identifies the office from which the FA is issued, the date and time of issue, the product name, the valid times and the states and/or areas covered by the FA.
b. Precautionary statement section - between the communications/product headers and the body of the forecast are three precautionary statements which are in all Area Forecasts: IFR/MTN OBSC, TSTMS, and NON MSL HGTS.
c. Synopsis section - a brief summary of the location and movement of fronts, pressure systems, and circulation patterns for an 18-hour period. References to low ceilings and/or visibilities, strong winds, or any other phenomena the forecaster considers useful, may also be included.
d. VFR Clouds and Weather section - contains a 12-hour specific forecast, followed by a six-hour (18-hour in Alaska) categorical outlook giving a total forecast period of 18 hours (30 hours in Alaska). The VFR CLDS/WX section is usually several paragraphs long. The breakdown may be by states or by well-known geographical areas. The specific forecast section gives a general description of clouds and weather which cover an area greater than 3,000 square miles and is significant to VFR flight operations.
AC 00-45E
D. Aviation Weather Forecasts
4. What are in-flight Aviation Weather Advisories (WST, WS, WA)?
Inflight aviation weather advisories are forecasts to advise en-route aircraft of development of potentially hazardous weather, in 3 types: the SIGMET, AIRMET and Convective SIGMET. All heights are referenced MSL, except in the case of ceilings CIG, which indicate AGL.
AC 00-45E
D. Aviation Weather Forecasts
5. What is a Convective SIGMET?
Convective SIGMETs (WST) implies severe or greater turbulence, severe icing and low-level wind shear. They may be issued for any convective situation which the forecaster feels is hazardous to all categories of aircraft. Convective SIGMET bulletins are issued for the Eastern (E), Central (C) and Western (W) United States (Convective SIGMETs are not issued for Alaska or Hawaii). Bulletins are issued hourly at H+55. The text of the bulletin consists of either an observation and a forecast, or just a forecast. The forecast is valid for up to 2 hours.
a. Severe thunderstorm due to:
*Surface winds greater than or equal to 50 knots.
*Hail at the surface greater than or equal to 3/4 inches in diameter.
*Tornadoes
b. Embedded thunderstorms
c. A line of thunderstorms
d. Thunderstorms producing greater than or equal to heavy precipitation that affects 40% or more of an area at least 3,000 square miles.
AC 00-45E
D. Aviation Weather Forecasts
6. What is a SIGMET (WS)?
A SIGMET advises of non-convective weather that is potentially hazardous to all aircraft. SIGMETs are issued for the six areas corresponding to the FA areas. The maximum forecast period is four hours. In the conterminous U.S., SIGMETs are issued when the following phenomena occur or are expected to occur:
a. Severe icing not associated with a thunderstorm;
b. Severe or extreme turbulence or clear air turbulence (CAT) not associated with a thunderstorm;
c. Dust-storms or sandstorms lowering surface or in-flight visibilities to below 3 miles;
d. Volcanic ash.
AC 00-45E
D. Aviation Weather Forecasts
7. What is an AIRMET (WA)?
Advisories of significant weather phenomena that describe conditions at intensities lower than those which require the issuance of SIGMETs, intended for use by all pilots in the pre-flight and en-route phase of flight to enhance safety. AIRMET Bulletins are issued every 6 hours beginning at 0145 UTC during Central Daylight Time and at 0245 UTC during Central Standard Time. Unscheduled updates and corrections are issued as necessary.

Each AIRMET Bulletin includes an outlook for conditions expected after the AIRMET valid period. AIRMETs contain details about IFR, extensive mountain obscuration, turbulence, strong surface winds, icing, and freezing levels.
AC 00-45E
D. Aviation Weather Forecasts
8. What is a TWEB?
NWS offices prepare transcribed weather broadcast (TWEB) text products for the contiguous U.S., including synopsis and forecast for more than 200 routes and local vicinities. TWEB products are valid for 12 hours and are issued 4 times a day at 0200Z, 0800Z, 1400Z, and 2000Z in a variety of sources (TIBS, PATWAS, and more).

A TWEB route forecast or vicinity forecast will not be issued if the TAF for that airport has not been issued. A TWEB route forecast is for a 50-NM wide corridor along a line connecting the end points of the route. A TWEB local vicinity forecast covers an area within a radius of 50 NM. These forecasts describe sustained surface winds (25 knots or greater), visibility, weather and obscuration to vision, sky conditions (coverage and ceiling/cloud heights), mountain obscurement, and non-convective low-level wind shear.
AC 00-45E
D. Aviation Weather Forecasts
9. What is a Winds and Temperatures Aloft Forecast (FD)?
Winds and temperatures aloft are forecasted for specific locations in the contiguous U.S., and also prepared for a network of locations in Alaska and Hawaii. Forecasts are made twice daily based on the 00Z and 12Z radiosonde data for use during specific time intervals. FDs contain the following characteristics:
a. The valid time period the FD may be used, and a notation "TEMPS NEG ABV 24000." Since temperatures above 24,000 feet are always negative, the minus sign is omitted.
b. "FT" indicates the levels of the wind and temperature data. Through 12,000 feet the levels are true altitude. From 18,000 feet and above, the levels are pressure altitude.
c. A 4-digit group shows wind direction in tens of degrees, and the second 2 digits are the wind speed in knots. A 6-digit group includes forecast temperatures in degrees Celsius.
d. No winds are forecasted within 1,500 feet of the station elevation.
e. No temperatures are forecasted for any level within 2,500 feet of the station elevation.
f. If a wind direction is coded between 51 and 86, the wind speed is 100 knots or greater.
g. If the wind speed is forecasted to be 200 knots or greater, the wind group is coded as 99 knots.
h. When the forecast speed is less than 5 knots, the codes group is "9900" which means, "Light and Variable."
AC 00-45E
D. Aviation Weather Forecasts
10. What valuable information can be determined from Winds and Temperatures Aloft Forecasts (FD)?
Most favorable altitude - based on winds and direction of flight.

Areas of possible icing - by noting air temperatures of +2C to -20C.

Temperature inversions.

Turbulence - by observing abrupt changes in wind direction and speed at different altitudes.
AC 00-45E
D. Aviation Weather Forecasts
11. What are Center Weather Advisories (CWA)?
A Center Weather Advisory (CWA) is an aviation warning for use by aircrews to anticipate and avoid adverse weather conditions in the en route and terminal environments. The CWA is not a flight planning product; instead it reflects current conditions expected to begin within 2 hours of issuance. CWAs are valid for a maximum of 2 hours. If conditions are expected to continue beyond the 2-hour valid period, a statement will be included in the CWA.
AC 00-45E
D. Aviation Weather Forecasts
12. What is a Convective Outlook (AC)?
A national forecast of thunderstorms, in 2 parts: Day 1 Convective Outlook (first 24 hours), and Day 2 Convective Outlook (next 24 hours). Describe areas in which there is a slight, moderate, or high risk of severe thunderstorms. The time of issuance for Day 1 are 0600Z, 1300Z, 1630Z, 2000Z, and 0100Z. The initial Day 2 issuance is at 0830Z during standard time and 0730Z during daylight time, updated at 1730Z. The AC is a flight planning tool used to avoid thunderstorms.
AC 00-45E
E. Aviation Weather Charts
1. Give some examples of current weather charts available at the FSS or NWSO used in flight planning.
a. Surface Analysis Chart
b. Weather Depiction Chart
c. Radar Summary Chart
d. Significant Weather Prognostic Chart
e. Winds and Temperatures Aloft Chart
f. Composite Moisture Stability Chart
g. Convective Outlook Chart
h. Constant Pressure Analysis Chart
i. Volcanic Ash Forecast Transport and Dispersion Chart
AC 00-45E
E. Aviation Weather Charts
2. What is a Surface Analysis Chart?
This is a computer-prepared chart that covers the contiguous 48 states and adjacent areas. The chart is transmitted every three hours. The surface analysis chart provides a ready means of locatiing pressure systems and fronts. It also gives an overview of winds, temperatures and dew point temperatures at chart time. When using the chart, keep in mind that weather moves and conditions change. Using the surface analysis chart in conjunction with other information gives a more complete weather picture.
AC 00-45E
E. Aviation Weather Charts
3. What information does a Weather Depiction Chart provide?
The weather depiction chart is a computer-generated (with weather observer's analysis of fronts) from METAR reports. This chart gives a broad overview of the observed flying category conditions at the valid time of the chart. The chart begins at 01Z each day, if transmitted at 3-hour intervals, and is valid at the time of the plotted data. The plotted data for each station area are total sky cover, cloud height or ceiling, weather and obstructions to vision and visibilities. The weather depiction chart is an ideal place to begin preparing for a weather briefing and flight planning. From this chart one can get a "bird's eye" view of areas of favorable and adverse weather conditions at chart time.
AC 00-45E
E. Aviation Weather Charts
4. Define the terms: IFR, MVFR and VFR.
IFR: Ceilings less that 1,000 and/or visibilities less than 3 miles (Instrument Flight Rules)

MVFR: Ceiling 1,000 to 3,000 feet inclusive and/or visibility 3 to 5 miles inclusive (Marginal VFR)

VFR: No ceiling, or ceiling greater than 3,000 and visibility greater than 5 miles (Visual Flight Rules)
AC 00-45E
E. Aviation Weather Charts
5. What are Radar Summary Charts?
Computer-generated graphical display of a collection of automated radar weather reports (SDs). The chart displays areas of precipitation, coverage, echo top, and cell movement of precipitation. Severe weather watches are plotted if they are in effect when the chart is valid. The chart is available hourly with a valid time of 35 minutes past each hour.

This chart aids in pre-flight planning by identifying general areas and movement of precipitation and/or thunderstorms. Displays drops or ice particles of precipitation size only; it does not display clouds or fog. Therefore, since the absence of echoes does not guarantee clear weather, and cloud tops will most likely be higher than the tops of the precipitation echoes detected by radar, the radar summary chart must be used along with other charts, reports, and forecasts for best effectiveness.
AC 00-45E
E. Aviation Weather Charts
6. What are Significant Weather Prognostic Charts?
Call "progs," these charts portray forecasts of selected weather conditions at specified valid times (12, 24, 36, and 48 hour progs). Each valid time is the time at which the forecast conditions are expected to occur, made from a comprehensive set of observed weather conditions. The observed conditions are extended forward in time and become forecasts by considering atmospheric and environmental processes. Forecast information for the surface to 24,000 feet is provided by the low-level significant weather prog chart. Forecast information from 24,000 to 60,000 feet is provided by the high-level significant weather prog chart.
AC 00-45E
E. Aviation Weather Charts
7. Describe the U.S. Low-Level Significant Weather Prog Chart.
It is a "Day One" forecast of significant weather for the conterminous U.S., pertaining to the level from surface to FL240 (400 mb). With two forecast periods, 12 hours and 24 hours, the chart is composed of four panels. The two lower panels depict the 12- and 24-hour surface progs, and the two upper panels depict the 12- and 24-hour significant weather progs. Issued four times a day at 00Z, 06Z, 12Z, and 18Z. Covered are forecast positions and characteristics of pressure systems, fronts, and precipitation. Much insight can be gained by evaluating the individual fields of pressure patterns, fronts, precipitation, weather flying categories, freezing levels, and turbulance displayed on the chart.
AC 00-45E
E. Aviation Weather Charts
8. What is a Forecast Winds and Temperatures Aloft Chart (FD)?
This chart is a computer-generated chart depicting both observed and forecast winds and temperatures aloft. Forecast winds and temperatures aloft are prepared for eight levels on eight separate panels. The levels are 6,000, 9,000, 12,000, 18,000, 24,000, 30,000, 34,000, and 39,000 feet MSL. They are available daily as 12-hour progs at 1200Z and 0000Z. These charts are typically used to determine winds at a proposed altitude or to select the best altitude for a proposed flight. Temperatures also can be determined from the forecast charts. Interpolation must be used to determine winds and temperatures at a level between charts and data when the time period is other than the valid time of the chart.
AC 00-45E
E. Aviation Weather Charts
9. What is a Composite Moisture Stability Chart?
This is an analysis chart using observed upper air data. The chart is composed of four panels including stability, freezing level, precipitable water and, average relative humidity. This computer-generated chart is available twice daily with valid times of 12Z and 00Z. It is used to determine the characteristics of a particular weather system in terms of stability, moisture, and possible aviation hazards. Generally, these characteristics tend to move with the associated weather systems, such as lows, highs, and fronts. Exercise caution, as modification of these characteristics could occur through development, dissipation, or the movement of the system.
AC 00-45E
E. Aviation Weather Charts
10. What is a Convective Outlook Chart?
This chart depicts areas forecast to have thunderstorms, and is presented in two panels. The left-hand panel is the Day 1 Convective Outlook, and the right-hand panel is the Day 2 Convective Outlook. "Day 1" outlines areas in the continental U.S. where thunderstorms are forecasted during that period. It is issued five times daily (0600Z, 1300Z, 1630Z, 2000Z, and 0100Z) and all issuances are valid until 12Z the following day. The outlook issued qualifies the level of risk (i.e., SLGT, MDT, HIGH) as well as the areas of general thunderstorms.

The Day 2 Convective Outlook contains the same information as the Day 1 chart, and is issued twice a day (0830Z and 1730Z) in a period from 12Z the following day to 12Z the next day.
AC 00-45E
E. Aviation Weather Charts
11. What are Constant Pressure Analysis Charts?
Any surface of equal pressure in the atmosphere is a constant pressure surface. A constant pressure analysis chart is an upper air weather map where all information depicted is at the specified pressure of the chart. From these charts, a pilot can approximate the observed air temperature, wind, and temperature-dew-point spread along a proposed route. They also depict highs, lows, troughs, and ridges aloft by the height contour patterns resembling isobars on a surface map. Twice daily, six computer-prepared constant pressure charts are transmitted by facsimile for six pressure levels:
850 mb......5,000 ft
700 mb....10,000 ft
500 mb....18,000 ft
300 mb....30,000 ft
250 mb....34,000 ft
200 mb....39,000 ft
AC 00-45E
E. Aviation Weather Charts
12. Describe a Volcanic Ash Forecast Transport and Dispersion Chart.
The VAFTAD chart presents the relative concentrations of ash following a volcanic eruption for three layers of the atmosphere in addition to a composite of ash concentration through the atmosphere. The chart focuses on hazards to aircraft flight operations caused by volcanic eruption with an emphasis on the ash cloud location in time and space. It uses National Centers for Environmental Prediction forecast data to determine the location of ash concentrations over 6-hour and 12-hour time intervals. The chart is strictly for advanced flight planning purposes. It is not intended to take the place of SIGMETs regarding volcanic eruptions and ash.
AC 00-45E