Chapter 2: Weather

A. Nature of the Atmosphere 9. At what rate does atmospheric pressure decrease with an increase in altitude? (AC 00-6A)

1" Hg per 1,000'

A. Nature of the Atmosphere 24. What are the three stages of a thunderstorm? (AC 00-6A)

1. Cumulus stage - updrafts cause raindrops to increase in size. 2. Mature stage - Rain at earth's surface; it falls through or immediately beside the updrafts; lightning; perhaps roll clouds. 3. Dissipating stage - Downdrafts and rain begin to dissipate.

A. Nature of the Atmosphere 27. Name several types of fog (AC 00-6A)

1. Radiation fog 2. Advection fog 3. Upslope fog 4. Precipitation-induced fog 5. Ice fog

A. Nature of the Atmosphere 4. What are the standard temperature and pressure values for seal level? (AC 00-6A)

15°C 29.92" Hg

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 degrees and the dew point is 62 degrees? (AC 00-6A)

86-62 = 20 20/4 = 5 (or 4.4) 5 x 1000 = 5,000' AGL

C. Aviation Weather Reports 1. What is a METAR and what are the two types? (AC 00-45)

A METAR is an hourly surface observation of conditions observed at an airport. Two types: Routine METAR report - transmitted every hour Aviation Selected Special Weather report (SPECI) - can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information

D. Aviation Weather Forecasts 6. What is a SIGMET (WS)? (AC 00-45)

A SIGMET (WS) 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 US, 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 thunderstorms c. Dust storms or sandstorms lowering surface or in-flight visibility to below 3 miles d. Volcanic ash

D. Aviation Weather Forecasts 1. What are Terminal Aerodrome Forecasts (TAFs)? (AC 00-45)

A TAF is a concise statement of the expected meteorological conditions significant to aviation for a specified time period within five statute miles (SM) of the center of the airport's runway complex (terminal). The TAFs use the same weather codes found in METAR weather reports, in the following format: a. Type of reports b. ICAO station identifier c. Date and time of origin d. Valid period date and time e. Forecasts

Additional Study Questions 6. What is a sea breeze, and why does it occur? (AC 00-6)

A coastal breeze blowing from sea to land caused by the temperature difference when the land surface is warmer than the sea surface. Sea breeze usually occurs during the day.

C. Aviation Weather Reports 5. What are Radar Weather Reports (SD)? (AC 00-45)

A radar weather report (SD/ROB) contains information about precipitation observed by weather radar. It is a textual product derived from the WSR-88D NEXRAD radar without human intervention. Reports are transmitted hourly and contain the following: location ID, time, configuration (CELL, LN, and AREA), coverage, precipitation type and intensity, location, maximum tops, cell movement, and remarks. The resolution of an SD/ROB is very coarse, up to 80 minutes old, and should only be used if no other radar information is available.

A. Nature of the Atmosphere 3. What is a "ridge?" (AC 00-6A)

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.

A. Nature of the Atmosphere 2. What is a "trough?" (AC 00-6A)

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.

D. Aviation Weather Forecasts 2. Define "aviation area forecast." (AC 00-45)

Abbreviated as "FA," this is a forecast of specified weather phenomena covering a flight information region or other area designated by the meteorological authority. Pilots should use the area forecast (in conjunction with AIRMETs, SIGMETs, convective SIGMETs, CWAs, etc.), to determine forecast en route weather and to interpolate conditions at airports that do not have a terminal aerodrome forecast (TAF). FAs are issued 3 times daily for each of the 6 areas in the contiguous 48 states. FAs are also issued for the Gulf of Mexico, the Caribbean, Hawaii, and Alaska.

A. Nature of the Atmosphere 29. What is advection fog, and where is it most likely to form? (AC 00-6A)

Advection fog results form 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.

D. Aviation Weather Forecasts 7. What is an AIRMET (WA)? (AC 00-45)

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 to enhance safety. AIRMET information is available in two formats: text bulletins (WA) and graphics (G-AIRMET). They are issued on a scheduled basis every 6 hours beginning at 0245 UTC. 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.

A. Nature of the Atmosphere 25. What is a "temperature inversion?" (AC 00-6A)

An inversion is an increase in temperature with height - a reversal of the normal decrease with height. An inversion aloft permits warm rain to foll through cold air below. Temperature int he 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 air is stable, with little or no turbulence.

A. Nature of the Atmosphere 5. What are "isobars?" (AC 00-6A)

An isobar is a line on a weather chart which connects areas of equal or constant barometric pressure.

E. Aviation Weather Charts 10. What are constant pressure analysis charts? (AC 00-45)

Any surface of equal pressure in the atmosphere is 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, five constant pressure charts are issued from observed data obtained at 00Z and 12Z: 850 mb .......... 5,000 ft 700 mb ........ 10,000 ft 500 mb ........ 18,000 ft 300 mb ........ 30,000 ft 200 mb ........ 39,000 ft

Additional Study Questions 10. If your destination has no Terminal Forecast, which primary source of information should be referenced for forecasted weather at the estimated time of arrival? (AC 00-45)

Area Forecast

D. Aviation Weather Forecasts 3. What information is provided by an FA? (AC 00-45)

Area forecasts are issued for the contiguous US and cover the airspace between the surface and 45,000' MSL. They include: a. SYNOPSIS - brief discussion of the synoptic weather affecting the FA area during the 18-hour valid period. b. CLOUDS AND WEATHER - description of the clouds and weather for the first 12-hour period for each state or group of states, including - Cloud amount (SCT, BKN, or OVC) for clouds with bases higher than or equal to 1,000' AGL and below FL 180 - Cloud bases and tops (AMSL) associated with the above - Precipitation - Visibilities between 3-6 SM and obstruction(s) to visibility - Sustained surface winds 20 KTS or greater c. 12 to 18 HOUR CATEGORICAL OUTLOOK - IFR, marginal VFR (MVFR), or VFR, including expected precipitation and/or obstruction(s) to visibility.

D. Aviation Weather Forecasts 11. What are Center Weather Advisories (CWA)? (AC 00-45)

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 at the time of issuance and/or is a short-range forecast for 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.

E. Aviation Weather Charts 6. What are short-range surface prognostic charts? (AC 00-45)

Called "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' is provided by the low-level significant weather prog chart. Forecast information from above 24,000-60,000' is provided by the high-level significant weather prog chart.

Additional Study Questions 8. Define the term "ceiling." (AC 00-6)

Ceiling = The heights above the earth's surface of the lowest layer of clouds or obscuring phenomena that is reported as broken, overcast, or obscuration, and not classified as thin or partial.

A. Nature of the Atmosphere 20. Name the three types of structural icing that may occur in flight. (AC 00-6A)

Clear ice - forms after initial impact when the remaining liquid portion of the drop flows out over the aircraft surface, gradually freezing as a smooth sheet of solid ice. Rime ice - forms when drops are small, such as those in stratified clouds or light drizzle. The liquid portion remaining after initial impact freezes rapidly before the drop has time to spread out over aircraft surface. Mixed ice - forms when drops vary in size or when liquid drops are intermingled with snow or ice particles. The ice particles become embedded in clear ice, building a very rough accumulation.

Additional Study Questions 4. What symbols are used to depict the following frontal systems on surface analysis charts? Cold Warm Stationary Occluded (AC 00-6)

Cold: blue triangles Warm: red semi-circles Stationary: blue triangles on one side; red semi-circles on the other Occluded: triangles and semi-circles on same side

E. Aviation Weather Charts 5. What are radar summary charts? (AC 00-45)

Computer-generated graphical display of a collection of automated radar weather reports (SDs). The chart displays areas of precipitation as well as information about type, intensity, configuration, 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 and 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.

D. Aviation Weather Forecasts 5. What is a Convective SIGMET (WST)? (AC 00-45)

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. Special bulletins are issued at any time as required and updated at H+55. The text of the bulletin consists of either an observation and a forecast, or just a forecast. The forecast is valid up to 2 hours. a. Severe thunderstorm due to: - surface winds greater than or equal to 50 KTS - hail at the surface greater than or equal to 3/4" 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.

A. Nature of the Atmosphere 10. What does "dew point" mean? (AC 00-6A)

Dew point is the temperature to which a sample of air must be cooled to attain the state of saturation.

Additional Study Questions 1. How can a pilot receive updated weather information in-flight? (AIM 7-1-5)

En Route Flight Advisory Service (EFAS) c. Contact flight watch by useing the name of the ARTCC facility identification serving the area of your location, followed by your aircraft identification, and the name of the nearest VOR to your position. The specialist needs to know this approximate location to select the most appropriate transmitter/receiver outlet for communications coverage. d. Charts depicting the location of the flight watch control stations (parent facility) and the outlets they use are contained int he A/FD. If you do not know in which flight watch area you are flying, initiate contact by using the words "Flight Watch," your aircraft ID, and the name of the nearest VOR. THe facility will respond using the name of the flight watch facility. [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' AGL to 17,000' MSL on a common frequency of 122.0 MHz. It is also known as "Flight Watch."]

B. Obtaining Weather Information 6. What is EFAS? (AIM 7-1-5)

En route Flight Advisory Service 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' AGL to 17,000' MSL on a common frequency of 122.0 MHz. It is also known as "Flight Watch."

B. Obtaining Weather Information 8. What is "flight information service" (FIS)? (AIM 7-1-11)

FIS is a method of receiving aviation weather and other operational data in the cockpit that augments traditional pilot voice communication with FSS or ATC facilities. It is not intended to replace traditional pilot and controller/FSS pre-flight briefings or in-flight voice communications.

B. Obtaining Weather Information 7. What is HIWAS? (AIM 7-1-10)

Hazardous In-flight Weather Advisory Service 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. Navaids with HIWAS capability are depicted on sectional charts with an "H" in the upper right corner of the identification box. Where implemented, HIWAS alerts are broadcast on all except emergency frequenceies once upon receipt by ARTCC, terminal facilities, and AFSS/FSSs.

D. Aviation Weather Forecasts 4. What are In-flight Aviation Weather Advisories (WST, WS, WA)? (AIM 7-1-6)

In-flight aviation weather advisories are forecasts to advise en route aircraft of development of potentially hazardous weather in 3 types: SIGMET Convective SIGMET AIRMET All heights are referenced MSL, except in the case of ceilings (CIG), which indicated AGL.

E. Aviation Weather Charts 7. Describe a U.S. low-level significant weather prog chart. (AC 00-45)

It is a "Day One" forecast of significant weather for the conterminous U.S., pertaining to the layer from surface to FL240 (400mb). 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 4 times a day at 0Z, 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 turbulence displayed on the chart.

E. Aviation Weather Charts 4. Define the terms: LIFR, IFR, MVFR, and VFR. (AIM 7-1-7)

LIFR - Low IFR - Ceiling less than 500' and/or visibility less than 1 mile IFR - Ceiling 500'-1000' and/or visibility 1-3 miles MVFR - Marginal VFR - Ceiling 1000'-3000' and/or visibility 3-5 miles VFR - Ceiling greater than 3,000' - Visibility greater than 5 miles - includes sky clear

A. Nature of the Atmosphere 1. State the general characteristics in regard to the flow of air around high and low pressure systems int he Northern Hemishpere. (AC 00-6A)

Low pressure - inward, upward, and counterclockwise High Pressure - outward, downward, and clockwise

D. Aviation Weather Forecasts 10. What valuable information can be determined from Winds and Temperatures Aloft Forecasts (FB)?

MOST FAVORABLE ALTITUDE - based on winds and direction of flight AREAS OF POSSIBLE ICING - by noting air temperatures of +2°C to -20°C TEMPERATURE INVERSIONS TURBULENCE - by observing abrupt changes in wind direction and speed at different altitudes

Additional Study Questions 7. What is a mountain wave? (AC 00-6)

Mountain waves occur when air is being blown over a mountain range or even the ridge of a sharp bluff area. As the air hits the upwind side of the range, it starts to climb, thus creating what is generally smooth updraft which turns into a turbulent downdraft as the air passes the crest of the ridge. From this point, for many miles downwind, there will be a series of downdrafts and updrafts. All it takes to form a mountain wave is wind blowing across the range at 15 KTS or more at an intersection angle of 30 degrees or more.

B. Obtaining Weather Information 3. Where can you find a listing of AFSS/FSS and weather information numbers? (AIM 7-1-2)

Numbers for these services can be found in the A/FD under the "FAA and NWS Telephone Numbers" section. They are also listed in the US Government section of the local telephone directory.

Additional Study Questions 2. Decode the following pilot weather report (PIREP): KCMH UA/OV KAPE 230010/TM 1516/FL085/TP BE20/SK BKN 065/WX FV03SM HZ F/TA 20/TB LGT (AIM 7-1-20)

Port Columbus International Airport Routine Pilot Report / In relation to a VOR location 230, 10 NM of Appleton airport time 15:16 zulu flight level 8,500ft aircraft type Super King Air 200 sky broken at 6500ft weather flight visibility 3 SM haze air temperature 20 degrees celsius light turbulence

Additional Study Questions 9. Give some examples of charts and reports useful in determining the potential for and location of thunderstorms along your route. (AC 00-45)

Reports: SIGMETs Convective SIGMETs AIRMETs PIREPs METARs Area Forecast (AF) TAFs Winds and Temps Aloft Charts: Prog Charts Low/Mid/High Level SIGWX Progs Surface Analysis RADAR Pressure Charts

A. Nature of the Atmosphere 14. Effects of Stable and Unstable Air on Clouds, Turbulence, Precipitation, and Visibility (AC 00-6A)

Stable Clouds - Stratiform Turbulence - Smooth Precipitation - Steady Visibility - Fair to Poor Unstable Clouds - Cumuliform Turbulence - Rough Precipitation - Showery Visibility - Good

B. Obtaining Weather Information 4. What types of weather briefings are available from an AFSS/FSS briefer? (AIM 7-1-4)

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 in Alaska only, 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. In-flight Briefing - Request when needed to update a pre-flight briefing

A. Nature of the Atmosphere 19. Name the main types of icing an aircraft may encounter in-flight. (AC 00-6A)

Structural Icing Induction System Icing Instrument Icing

A. Nature of the Atmosphere 8. Why do surface winds generally flow across the isobars at an angle? (AC 00-6A)

Surface friction

A. Nature of the Atmosphere 7. What causes the winds aloft to flow parallel to the isobars? (AC 00-6A)

The Coriolis force (and pressure-difference force)

E. Aviation Weather Charts 9. What is a convective outlook chart? (AC 00-45)

The convective outlook chart depicts areas forecast to have the potential for severe (tornado, wind gusts 50+ KTS, or hail 3/4" diameter size or greater) and non-severe (general) convection and specific severe weather threats during the following three days. The chart defines areas of slight risk (SLGT), moderate risk (MDT), or high risk (HIGH) of severe thunderstorms for a 24-hour period beginning at 1200 UTC. The Day 1 and Day 2 Convective Outlooks also depict areas of general thunderstorms (GEN TSTMS), while the Day 1, Day 2, and Day 3 Convective Outlooks may use SEE TEXT for areas where convection may approach or slightly exceed severe criteria.

A. Nature of the Atmosphere 21. What action is recommended if you inadvertently encounter icing conditions? (FAA-H-8083-15)

The first course of action should be to leave the area of visible moisture. This might mean descending to an altitude below the cloud bases, climbing to an altitude above the cloud tops, or turning to a different course.

A. Nature of the Atmosphere 17. What is the definition of the term freezing level and how can you determine where that level is? (AC 00-6A)

The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0°C. It is possible to have multiple freezing layers when a temperature inversion occurs above the defined freezing level. A pilot can use current icing products (CIP) and forecast icing products (FIP), as well as the freezing level graphics chart to determine the approximate freezing level. Other potential sources of icing information are: Area Forecasts PIREPs AIRMETs SIGMETs Surface Analysis Charts Low-level Significant Weather Charts Winds and Temperatures Aloft

A. Nature of the Atmosphere 28. What causes radiation fog to form? (AC 00-6A)

The ground cools the adjacent air to the dew point on calm, clear nights.

E. Aviation Weather Charts 8. Describe a mid-level significant weather (SIGWX) chart. (AC 00-45)

The mid-level signifcant weather chart provides a forecast and an overview of significant en route weather phenomena over a range of flight levels from 10,000' MSL to FL450, and associated surface weather features. The chart is a "snapshot" of weather expected at the specified valid time and depicts numerous weather elements that can be hazardous to aviation. The AWC issues the 24-hour mid-level significant weather chart four times daily.

B. Obtaining Weather Information 1. What is the primary means of obtaining a weather briefing? (AIM 7-1-2)

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).

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? (AC 00-6A)

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 close together) usually means wind speeds will be less.

A. Nature of the Atmosphere 12. What factor primarily determines the type and vertical extent of clouds? (AC 00-6A)

The stability of the atmosphere.

C. Aviation Weather Reports 4. What are PIREPs (UA), and where are they usually found? (AC 00-45)

The two types of PIREPs (routine = "UA," and urgent = "UUA") contain information concerning weather as 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 at least one eather element encountered (visibility in SM, distances 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.

E. Aviation Weather Charts 3. What information does a weather depiction chart provide? (AC 00-45)

The weather depiction chart is computer-generated (with a 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, is transmitted at three-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 in preparing for a weather briefing and flight planning. From this chart one can get a good idea of areas of favorable and adverse weather conditions at chart time.

D. Aviation Weather Forecasts 8. What are the different types of AIRMETs? (AIM 7-1-6)

There are three AIRMET types: Sierra, Tango, and Zulu a. Sierra - describes IFR conditions and/or extensive mountain obscurations b. Tango - describes moderate turbulence, sustained surface winds of 30 KTS or greater, and/or non-convective low-level wind shear c. Zulu - describes moderate icing and provides freezing level heights

E. Aviation Weather Charts 2. What is a surface analysis chart? (AC 00-45)

This is a computer-prepared chart that covers the contiguous 48 states and adjacent areas. The chart is transmitted every 3 hours. The surface analysis chart provides a ready means of locating 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.

A. Nature of the Atmosphere 13. How do you determine the stability of the atmosphere? (AC 00-6A)

Unstable air is indicated when temperature decreases uniformly and rapidly as you climb (approaching 3°C per 1,000'). If temperature remains unchanged or decreases only slightly with altitude, the air tends to be stable. Instability is likely when air near the surface is warm and moist. Surface heating, cooling aloft, converging or upslope winds, or an invading mass of colder air may lead to instability and cumuliform clouds.

A. Nature of the Atmosphere 30. What is upslope fog? (AC 00-6A)

Upslope fog forms as a result of moist, stable air being cooled adiabatically as it moves up sloping terrain. (Of, relating to, or being a reversible thermodynamic process that occurs without gain or loss of heat and without a change in entropy.) Once the upslope wind ceases, the fog dissipates. Upslope fog is often quite dense and extends to high altitudes.

A. Nature of the Atmosphere 18. What conditions are necessary for structural icing to occur? (AC 00-6A)

Visible moisture and below freezing temperatures at the point moisture strikes the aircraft.

A. Nature of the Atmosphere 11. When temperature and dew point are close together (within 5 degrees), what type of weather is likely? (AC 00-6A)

Visible moisture in the form of clouds, dew, or fog. Also, these are ideal conditions for carburetor icing.

A. Nature of the Atmosphere 32. Why is wind shear an operational concern for pilots? (AC 00-6A)

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 an departing from airports.

A. Nature of the Atmosphere 31. Define the term "wind shear," and state the areas in which it is likely to occur. (AC 00-6A)

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 in a frontal zone or thunderstorm. c. Clear air turbulence (CAT) at high levels associate with a jet stream or strong circulation.

D. Aviation Weather Forecasts 9. Describe the winds and temperature aloft forecasts (FB). (AC 00-45)

Winds and temperature aloft forecasts are computer prepared forecasts of wind direction, wind speed, and temperature at specified times, altitudes, and locations. They are produced 4 times daily for specified locations in the continental US, Hawaii, Alaska, and coastal waters,and the western Pacific Ocean. Amendments are not issued to the forecasts. Wind forecasts are not issued for altitudes within 1,500' of a location's elevation. Some of the features of FBs are: a. Product header includes date and time observations collected, forecast valid date and time, and the time period during which the forecast is to be used. b. Altitudes up to 15,000' referenced to MSL; altitudes at or above 18,000' are references to flight levels (FL). c. Temperature indicated in degrees Celsius (two digits) for the levels from 6,000'-24,000'. Above 24,000', minus sign is omitted since temperatures are always negative at those altitudes. Temperature forecasts are not issued for altitudes within 2,500' of a location's elevation. Forecasts for intermediate levels are determined by interpolation. d. Wind direction indicated in tens of degrees (two digits) with reference to true north and wind speed is given in knots (two digits). Light and variable wind or wind speeds of less than 5 knots are expressed by 9900. Forecaste wind speeds of 100-199 KTS are indicated by subtracting 100 from the speed and adding 50 to the coded direction. For example a forecast of 250 degrees, 145 knots, is encoded as 7545. Forecast wind speeds of 200 KTSor greater are indicated as a forecast speed of 199 KTS. For example, 779 is decoded as 270 degrees at 199 KTS or greater.

A. Nature of the Atmosphere 22. Is frost considered to be hazardous to flight? Why? (AC 00-6A)

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 airflow. This slowing of the air causes early airflow separation, resulting in a loss of lift. Even a small amount of frost on airfoils any 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.

3. Decode the following METAR and TAF: a. METAR KPIT 091955Z COR 22015G25KT 3/4SM R28L/2600FT TSRA OVC010CB 18/16 A2992 RMK SLP045 T01820159 b. TAF KPIT 091730Z 0918/1024 15005KT 5SM HZ FEW020 WS010/31022KT c. FM091930 30015G25KT 3SM SHRA OVC015 d. TEMPO 0920/0922 1/2SM +TSRA OVC008CB e. FM100100 27008KT 5SM SHRA BKN020 OVC040 f. PROB30 1004/1007 1SM RA BR g. FM101015 18005KT 6SM SHRA OVC020 h. BECMG 1013/1015 P6SM NSW SKC (AIM 7-1-3)

a. METAR Report Pittsburgh the 9th @ 19:55 zulu corrected winds 220 @ 15 KTS gusting to 25 KTS 3/4 SM visibility runway visual range for RWY 28L is 2600ft thunderstorms and rain overcast cumulonimbus at 1,000ft temp 18/dew point 16 altimeter 29.92 remarks Sea Level Pressure in hectopascals hourly temperature and dew point: 0 = positive 18.2 = temp disseminated to the nearest 10th 0 = positive 159 dew point disseminated to the nearest 10th 15.9 b. TAF report Pittsburgh 9th @ 17:30 zulu valid period: 9th @ 17:00 zulu to 10th @ 24:00 zulu wind 150 at 5 KTS 5 SM visibility haze few clouds at 2000ft wind shear from surface to 1000ft; 310 at 22 KTS c. from the 9th at 19:30 wind 300 @ 15 KTS gusting to 25 KTS 3 SM visibility rain showers overcast at 1500ft d. temporary 9th at 20:00 to 9th at 22:00 1/2 SM visibility thunderstorms nd rain overcast cumulonimbus at 800ft e. from 10th @ 1:00 zulu wind 270 at 8 KTS 5 SM visibility rain showers broken at 2,000ft overcast at 4,000ft f. probability 10th @ 4:00 zulu to 10th @ 7:00 zulu visibility 1 SM rain mist g. from 10th at 10:15 zulue wind 180 at 5 KTS visibility 6 SM rain showers overcast 2,000ft h. BECMG 1013/1015 P6SM NSW SKC becoming 10th at 1300 zulu to 10th at 1500 zulu more than 6 SM visibility no significant weather sky clear

B. Obtaining Weather Information 5. What pertinent information should a weather briefing include? (AIM 7-1-4)

a. Adverse Conditions b. VFR Flight 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 FSS briefers upon requestion: - information on special use airspace (SUA) and SUA-related airspace, including alert areas, MOAs, MTRs (IFR, VFR, VR, and SR training routes), warning areas, and ATC assigned airspace (ATCAA) - a review of the printed NOTAM publication - approximate density altitude data - information on air traffic services and rules - customs/immigration procedures - ADIZ rules - search and rescue - LORAN-C and military NOTAMs - runway friction measurement value NOTAMs - GPS RAIM availability - other assistance as required

A. Nature of the Atmosphere 26. State two basic ways that fog may form. (AC 00-6A)

a. Cooling air to the dew point b. Adding moisture to the air near the ground

A. Nature of the Atmosphere 16. During your preflight planning, what type of meteorological information should you be aware of with respect to icing? (AC 91-74)

a. Location of fronts - A front's location, type, speed, and direction of movement. b. Cloud layers - The location of cloud bases and tops, which is valuable when determining if you will be able to climb above icing layers into warmer air; reference PIREPs and area forecasts. c. Freezing level(s) - Important when determining how to avoid icing and how to exit icing conditions if accidentally encountered. d. Air temperature and pressure - Icing tends to be found in low-pressure areas and at temperatures at or around freezing.

C. Aviation Weather Reports 3. Describe several types of weather observing programs available. (AIM 7-1-12)

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 sub-system, and a transmitter to broadcast local, minute-by-minute weather data directly to the pilot. Observations will include the prefix AUTO in data. c. ASOS/AWSS - Automated Surface Observing System/Automated Weather Sensor System; the primary US surface weather observing systems. AWSS is a follow-on program that provides the identical data as ASOS. Both systems provide continuous minute-by-minute observations that generate METARs and other aviation weather information. Transmitted over a discrete VHF radio frequency or the voice portion of a local NAVAID, and are receivable to a maximum of 25 NM from the station and a maximum altitude of 10,000' AGL. Observations made without human intervention will include the modifier "AUTO" in the report data.

Additional Study Questions 5. What is a microburst? When and where are they most likely to occur? (AIM 7-1-26)

a. Microbursts are small scale intense downdrafts which, on reaching the surface, spread outward in all directions from the downdraft center. This causes the presence of both vertical and horizontal wind shears that can be extremely hazardous to all types and categories of aircraft, especially at low altitudes. Due to their small size, short life span, and the fact that they can occur over areas without surface precipitation, microbursts are not easily detectable using conventional weather radar or wind shear alert systems. b. Parent clouds producing microburst activity can be any of the low or middle layer convective cloud types. However, microbursts commonly occur within the heavy rain portion of thunderstorms, and in much weaker, benign appearing convective cells that have little or no precipitation reaching the ground. Microbursts can be found almost anywhere that there is convective activity. -heavy rain associated with a thunderstorm -light rain in benign appearing virga Can last 15 minutes to an hour. e. Microburst wind shear may create a severe hazard for aircraft within 1,000ft of the ground, particularly during landing and takeoff.

A. Nature of the Atmosphere 23. What factors must be present for a thunderstorm to form? (AC 00-6A)

a. Sufficient water vapor b. An unstable lapse rate c. An initial upward boost (lifting) to start the storm process in motion

E. Aviation Weather Charts 1. Give some examples of current weather harts available at the FSS or NWSO used in flight planning. (AC 00-45)

a. Surface analysis chart b. Weather depiction chart c. Radar summary chart d. Short-range surface prognostic chart e. Significant weather prognostic chart f. Convective outlook chart g. Constant pressure analysis chart

C. Aviation Weather Reports 2. Describe the basic elements of a METAR. (AC 00-45)

a. TYPE OF REPORTS - the METAR, and the SPECI (aviation special weather report) b. ICAO station identifier - 4-letter station identifiers; in the contiguous US, the 3-letter identifier is prefixed with K. c. DATE AND TIME OF REPORT - a 6-digit date/time gropu appended with Z (UTC). First two digits are the date, then two for the hour, and two for 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, AO1 or AO2 will be encoded in the remarks section to indicate the type of precipitation sensor used at the station. e. WIND - 5-digit group (6 digits if speed is over 99 KTS); 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 KTS, the next three digits). f. VISIBILITY - surface visibility in statute miles, space, fractions of statute miles (as needed), and the letters SM. g. RUNWAY VISUAL RANGE (RVR), as required h. WEATHER PHENOMENA - broken into two categories: qualifiers and weather phenomena. i. SKY CONDITION - amount/height/type (as required) or indefinite ceiling/height (vertical visibility). Heights are recorded in feet AGL. 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.

B. Obtaining Weather Information 2. What are some examples of other sources of weather information? (AIM 7-1-2)

a. Telephone Information Briefing Service (TIBS) (AFSS). b. Weather and aeronautical information available from numerous private industry sources. c. Direct User Access Terminal System (DUATS) can be accessed by pilots with a current medical certificate toll-free in the 48 contiguous states via personal computer. d. In Alaska, Transcribed Weather Broadcast (TWEB) and telephone access to the TWEB (TEL-TWEB).

A. Nature of the Atmosphere 33. What types of weather information will you examine to determine if wind shear conditions might affect your flight? (AC 00-54)

a. Terminal forecasts - any mention of low level wind sheer (LLWS) or the possibility of severe thunderstorm, heavy rain showers, hail, and wind gusts suggest the potential for LLWS and microbursts b. METARs - inspect for ay indication of thunderstorms, rain showers, or blowing dust. Additional signs such as warming trends, gusty winds, cumulonimbus clouds, etc., hsould be noted. c. Severe weather watch reports, SIGMETs, and convetive SIGMETs - severe convective weather is a prime source for wind shear and microbursts. d. LLWAS (low level wind shear alert system) reports - installed at 110 airports in the US; designed to detect wind shifts between outlying stations and a reference centerfield station. e. PIREPs - reports of sudden airspeed changes on departure or approach and landing corridors provide a real-time indication of the presence o wind shear.