Chapter 3: Weather Information

Define "aviation area forecast".

-Abbreviated as "FA." -Forecast of specified weather phenomena covering a flight information region or other area designated by meteorological authority. -Issued 3 times daily for each of the 6 areas in the contiguous 48 states. Also issued for the Gulf of Mexico, Caribbean, Hawaii, and Alaska.

What are Center Weather Advisories (CWA)?

-An aviation warning for use by aircrews to anticipate and avoid adverse weather conditions in the enroute and terminal environments. -Not a flight planning product; 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.

What is HIWAS?

-Hazardous In-Flight Weather Advisory Service (HIWAS): continuous broadcast of in-flight weather advisories including summarized Aviation Weather Warnings, SIGMETs, Convective SIGMETs, Center Weather Advisories, AIRMETs, and urgent PIREPs. -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 frequencies once upon receipt by ARTCC, terminal facilities, and AFSS/FSSs.

At what rate does atmospheric pressure decrease with an increase in altitude?

1" Hg per 1,000 feet

What are the standard temperature and pressure values for sea level?

15 C and 29.92" Hg

What is a METAR and what are the two types?

A METAR is an hourly surface observation of conditions observed at an airport. Two types: 1) routine transmitted every hour; 2) aviation selected special weather report (SPECI), which is a special report that can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information.

Describe the basic elements of a METAR.

A METAR report contains the following elements in order as presented: a. Type of reports: the METAR and the SPECI b. ICAO station identifier c. Date and time of report; 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 use, 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 (six 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 f. Visibility: surface visibility in statute miles g. Runway visual range (RVR) as required Weather phenomena i. Sky condition j. Temperature/dew point: 2 digit format in whole degrees Celsius; temperatures below zero are prefixed with M k. Altimeter l. Remarks (RMK) as required

What is a SIGMET (WS)?

A SIGMET (WS) advises of non-convective weather that is potentially hazardous to all aircraft. SIGMET5 are issued for the six areas corresponding to the FA areas. The maximum forecast period is four hours. In the conterminous United States, 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 visibilities to below 3 miles. d. Volcanic ash.

What is a Convective SIGMET?

A convective SIGMET (WST) implies severe or greater turbulence, severe icing and low-level wind shear. It 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, which 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 percent or more of an area at least 3,000 square miles.

If your route of flight takes you towards a low-pressure system, in general, what kind of weather can you expect? What if you were flying towards a high-pressure system?

A low-pressure system is characterized by rising air, which is conducive to cloudiness, precipitation, and bad weather. A high-pressure system is an area of descending air which tends to favor dissipation of cloudiness and good weather.

What are PIREPs (UA) and where are they usually found?

A pilot report (PIREP) provides valuable information regarding the conditions as they actually exist in the air, which cannot be gathered form any other source. Pilots can confirm the height of bases and tops of clouds, locations of wind shear and turbulence, and the location of inflight icing. There are two types of PIREPS: routine or "UA", and urgent or "UUA." PIREPS should be given to the ground facility with which communications are established (i.e., FSS, ARTCC, or terminal ATC). Altitudes are MSL, visibilities SM, and distances in NM. PIREPs are available from an FSS and on the internet via the ADDS web page.

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.

What are Terminal Aerodrome Forecasts (TAFs)?

A terminal aerodrome forecast (TAF) is a concise statement of the expected meteorological conditinos significant to aviation for a specified time period within five statue miles (SM) of the center of the aiport's runway complex (terminal). The TAFs use the same weather codes found in METAR weather reports, in the following format: a. Types of reports - a routine forecast (TAF), an amended forecast (TAF AMD), or a corrected forecast (TAF COR). b. ICAO station identifier - 4-letter station indentifiers. c. Date and time of origin - the date/time of forecast follows the terminal's location identifier. It contains the day of the month in two digits and time in four digits in which the forecast is completed and ready for transmission, with a Z appended to denote UTC. Example: 061737Z - the TAF was issued on the 6th day of the month at 1737 UTC. d. Valid period date and time - the first two digits are the day of the month for the start of the TAF followed by two digits indicating the starting hour (UTC). The next two digits indicate the day of the month for the end of the TAF, and the last two digits are the ending hour (UTC) of the valid period. Scheduled 24-hour and 30-hour TAFs are issued four (4) times per day, at 0000, 0600, 1200, and 1800Z. Example: A 00Z TAF issued on the 9th of the month and valid for 24 hours would have a valid period of 0900/0924. e. Forecasts - wind, visibility, significant and vicinity weather, cloud and vertical obscuration, non-convective low level wind shear, forecast change indicators (FM, TEMPO and PROB).

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 conductive to cloudiness and precipitation; hence the general association of low pressure and bad weather.

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.

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 preflight and enroute 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. Each AIRMET includes an outlook for conditions expected after the AIRMET valid period, and contain details about IFR, extensive mountain obscuration, turbulence, strong surface winds, icing, and freezing levels.

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 rain 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 air is stable, with little or no turbulence.

What are "isobars"?

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

What are the 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 ternperature/dewpoint 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: 850mb -- 5,000 ft 700mb -- 10,000 ft 500mb -- 18,000 ft 300mb -- 30,000 ft 250mb -- 34,000 ft 200mb -- 39,000 ft

What information is provided by an FA?

Area forecasts are issued for the conterminous U.S. and cover the airspace between the surface and 45,000 feet AMSL: 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 feet AGL and below FL180, - Cloud bases and tops (AMSL) associated with the above, - Precipitation, - Visibilities between 3 and 6 SM and obstruction(s) to visibility, - Sustained surface winds 20 knots or greater. c. 12 to 18-hour categorical outlook - IFR, marginal VFR (MVFR), or VFR, including expected precipitation and/or obstruction(s) to visibility.

Name the three types of structural icing that may occur in flight.

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.

List the effects of stable and unstable air on clouds, turbulence, precipitation and visibility.

Clouds - Strati form (stable), Cumuli form (unstable) Turbulence - Smooth (stable), Rough (unstable) Precipitation - Steady (stable), Showery (unstable) Visibility - Fair to poor (stable), Good (unstable)

What are the general characteristics of the weather a pilot would encounter when operating near a cold front? A warm front?

Cold front - As the front passes, expected weather can include towering cumulus or cumulonimbus, heavy rain accompanied by lightning, thunder and/or hail; tornadoes possible; during passage, poor visibility, winds variable and gusting; temperature/dew point and barometric pressure drop rapidly. Warm front- As the front passes, expected weather can include stratiform clouds, drizzle, low ceilings and poor visibility; variable winds; rise in temperature.

Descrieb the different types of fronts.

Cold front - Occurs when a mass of cold dense, and stable air advances and replaces a body of warmer air.\ Occluded front - A frontal occlusion occurs when a fast-moving cold front catches up with a slow-moving warm front. Two types: cold front occlusion and warm front occlusion. Warm front - The boundary area formed when a warm air mass contacts and flows over a colder air mass. Stationery front - When the forces of two air masses are relatively equal, the boundary or front that separates them remains stationary and influences the local weather for days. The weather is typically a mixture of both warm and cold fronts.

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.

What is a convective outlook chart?

Depicts areas of forecast to have potential for severe tornado, wind gusts greater than 50 knots, or hail 3/4-inch diamter size or great), and non severe convection and specific wx threats for the following three days. defines 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 genearl thunderstorms (GENTSTMS), 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.

What does "dew point" mean?

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

What is a "flight information service"?

Flight Information Service - Broadcast (FIS-B) is a ground broadcast service provided through the Automatic Dependent Surveillance - Broadcast (ADS-B) services network over the 978 MHz UAT data link. The FAA FIS-B system provides pilots and flight crews of properly-equipped aircraft with a flight deck display of aviation weather and aeronautical information.

What are the four types of Inflight Aviation Weather Advisories?

Inflight Aviation Weather Advisories are forecasts to advise enroute aircraft of the development of potentially hazardous weather in four types: the SIGMET (WS), the convective SIGMET (WST), the AIRMET (WA), and the center weather advisory (CWA). All heights are referenced MSL, except in the case of ceilings (CIG) which indicate AGL.

Define the terms: LIFR, IFR, MVFR and VFR.

LIFR -- Low IFR - ceiling less than 500 feet and/or visibility less than 1 mile. IFR -- Ceiling 500 to less than 1,000 feet and/or visibility 1 to less than 3 miles. MVFR -- Marginal VFR - ceiling 1,000 to 3,000 feet and/or visibility 3 to 5 miles inclusive. VFR -- Ceiling greater than 3,000 feet and visibility greater than 5 miles; includes sky clear.

During the preflight planning, what type of meteorological information should you be aware of with respect to icing?

Location of fronts - A font's location, type speed, and direction of movement. Cloud Layers - The location of cloud bases and tops, which is valuable when determining if you will be able to climb above icing layers or descend beneath those layers into warmer air; reference PIREPs or forecasts. Freezing levels - Important when determining how to avoid icing and how to exit icing conditinos if accidentally encountered. Air temperature and pressure - Icing tends to be found in low-pressure areas and at temperatures at or around freezing.

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

What valuable information can be determined from a Winds and Temperatures Aloft Forecast (FD)?

Most favorable altitude - based on winds and direction of flight. Areas of possible icing - by noting air temperatures of +2 degrees Celsius to - 20 degrees Celsius. Temperature Inversions. Turbulence - by observing abrupt changes in wind direction and speed at different altitudes.

You're planning a cross-country flight. Does the weather data provided by commercial and/or third party vendors satisfy the preflight action required by 14 CFR 91.103?

Pilots and operators should be aware that weather services provided by entities other than FAA, NWS or their contractors (such as the DUATS and Lockheed Martin Flight Services DUATS II) might not meet FAA/NWS quality control standards. All operators and pilots contemplating using such services should request and/or review an appropriate description of services and provider disclosure. When in doubt, consult with an FAA Flight Service Specialist.

What are short-range surface prognostic charts?

Short-range surface prognostic (prog) charts provide a forecast of surface pressure systems, fronts and precipitation for a 2-1/2 day period. They cover a forecast area of the 48 contiguous states and coastal waters, and are prepared by the NWS Weather Prediction Center. Predicted conditions are divided into five forecast periods: 12, 18, 24, 48 and 60 hours. Each chart depicts a snapshot of weather elements expected at the specified valid time. Charts are issued four times a day and can be used to obtain an overview of the progression of surface weather features during the included periods.

When significant precipitation is occurring at the surface, how thick can you expect the clouds to be?

Significant precipitation usually requires clouds to be at least 4,000 feet thick. The heavier the precipitation, the thicker the clouds are likely to be.

What types of weather briefings are available from an AFSS/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 in Alaska only, etc.). Abbreviated Briefing - Request when you need information to supplement mass disseminated dated, update a previous briefing, or when you need only one or two more 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.

Name the main types of icing an aircraft may encounter in-flight.

Structural, induction system, and instrument icing.

What is a surface analysis chart?

Surface analysis charts are analyzed charts of surface weather observations. The chart depicts the distribution of several items including sea level pressure, the positions of highs, lows, ridges, troughs, the location and character of fronts, and the various boundaries such as drylines, outflow boundaries, sea-breeze fronts, and convergence lines. Produced 8 times daily.

Why do surface winds generally flow across the isobars at an angle?

Surface friction

What causes the winds aloft to flow parallel to the isobars?

The Coriolis force

What is a Graphical Forecast for Aviation (GFA)?

The GFA is intended to provide the necessary aviation weather information as a complete picture of the weather that may impat flight in the continental U.S. the Webpae includes observational data, forecasts, and warnings that can be viewed from 14 hours in the past to 15 hours in the future, including thunderstorms, clouds, flight category, precipitation, icing, turbulence and wind.

What is the primary means of obtaining a weather briefing?

The fight service station (FSS) is the primary source for obtaining preflight briefings an inflight weather information. The FAA provides the Flight Service program through FSS's (both government and contract, 1-800-WX-BRIEF), and via the Internet, through Direct User Access Terminal System (DUATS), and Lockheed Martin Flight Services (DUATS II).

What action is recommended if you inadvertently encounter icing conditions?

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.

What is the definition of the term freezing level and how can you determine where that level is?

The freezing level is the lowest altitude in the atmosphere over a given location at which the air temperature reaches 0 degrees Celsius. 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, and winds and temperatures aloft (for air temperature at altitude).l

What causes radiation fog to form?

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

Describe a U.S. low-level significant weather prog chart.

The low-level significant weather (SIGWX) charts provide a forecast of aviation weather hazards primarily intended to be used as guidance products for pre-flight briefings. The forecast domain covers the continental U.S. and the coastal waters for altitudes Flight Level 240 and below. Each depicts a "snapshot" of weather expected at the specified valid time. The charts depict weather flying categories, turbulence, and freezing levels, and are issued four times per day in two types: a 12-hour and a 24-hour prog.

Describe a mid-level significant weather (SIGWX) chart.

The mid-level significant weather chart provides a forecast and an overview of significant en route weather phenomena over a range of flight levels from 10,000 feet 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. Produced 4 times daily.

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 close together_ usually means wind speeds will be less.

Explain the difference between a stable atmosphere and an unstable atmosphere. Why is the stability of the atmosphere important?

The stability of the atmosphere depends on its ability to resits vertical motion. A stable atmosphere makes vertical movement difficult, and small vertical disturbances dampen out and disappear. In an unstable atmosphere, small vertical air movements tend to become larger, resulting in turbulent airflow and convective activity. Instability can lead to significant turbulence, extensive vertical clouds, and severe weather.

What factor primarily determines the type and vertical extent of clouds?

The stability of the atmosphere.

What information does a weather depiction chart provide?

The weather depiction chart contains a plot of weather conditions at selected METAR stations and an analysis of weather flying category (VFR, MVFR, IFR). It is designed primarily as a briefing tool to alert aviation interests to the location of critical or near-critical operational minimums at terminals in the conterminous U.S. and surrounding land areas. Produced 8 times daily.

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 dissipates. Upslope fog is often quite dense and extends to high altitudes.

What conditions are necessary for structural icing to occur?

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

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.

Can onboard datalink weather (FIS-B) be useful in navigating an aircraft safely around an area of thunderstorms?

Weather data linked from a ground weather surveillance radar system is not real-time information; it displays recent rather than current conditions. This data is typically updated every 5 minutes, but can be as much as 15 minutes old by the time it displays in the cockpit. Therefore, FIS aviation weather products are not appropriate for tactical avoidance or severe weather such as negotiating a path through a weather hazard area.

Why is wind shear an operational concern to pilots?

Wind shear is an operational concern because unexpected changes in wind speed an direction can be potentially very hazardous to aircraft operations at low altitudes on approach to and departing from airports.

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

Describe the winds and temperature aloft forecasts (FB).

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 5 times daily for specified locations in the continental United States, 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 feet of a location's elevation. Features of FBs: 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 feet referenced to MSL; altitudes at or above 18,000 feet are references to flight levels (FL). c. Temperature indicated in degrees Celsius (two digits) for the levels from 6,000 through 24,000 feet. Above 24,000 feet minus sign is omitted since temperatures are always negative at those altitudes. Temperature forecasts are not issued for altitudes within 2,500 feet 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. Forecast wind speeds of 100 through 199 knots 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. Fore cast wind speeds of 200 knots or greater are indicated as a forecast speed of 199 knots. For example, 7799 is decoded as 270 degrees 199 knots or greater.

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 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 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.

What are the different types of AIRMETs?

a. AIRMET Sierra describes IFR conditions and/or extensive mountain obscurations. b. AIRMET Tango describes moderate turbulence, sustained surface winds of 30 knots or greater, and/or nonconvective low-level wind shear. AIRMET Zulu describes moderate icing and provides freezing level heights.

What pertinent information should a weather briefing include?

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 request: 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; runway friction measurement value NOTAMs; GPS RAIM availability; and other assistance as required.

State two basic ways that fog may form.

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

While en route, how can a pilot obatin updated weather information?

a. FSS on 122.2 and appropriate RCO (remote communication outlet) frequencies. b. ATIS broadcasts along your route of flight. c. HIWAS (Hazardous Inflight Weather Advisory Service). d. Datalink weather - cockpit display of FIS-B informatino. e. ATC (workload permitting).

Describe several types of weather observing programs available.

a. Manual Observations - with only a few exceptions, these reports are from airport locations staffed by FAA personnel who manually observe, perform calculations, and enter their observations into the communication system. 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 U.S. 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 feet AGL. Observations made without human intervention will include the modifier "AUTO" in the report data.

Name several types of fog.

a. Radiation fog b. Advection fog c. Upslope fog d. Frontal or precipitation-induced fog e. Steam fog

What factors must be present for a thunderstorm to form?

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

Give some examples of the various NWS weather charts you will use during preflight planning.

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

What are some examples of outher sources of weather information?

a. Telephone Information Briefing Service, or TIBS (FSS). b. Weather and aeronautical information available from numerous private industry sources. c. DUATS and Lockheed Martin Flight Services via the internet. Pilots with a current medical certificate can receive preflight weather data and file domestic VFR and IFR flight plans. d. In Alaska, Transcribed Weather Broadcast (TWEB) and telephone access to the TWEB, or TEL-TWEB).

What types of weather information will you examine to determine if wind shear conditions might affect your flight?

a. Terminal forecasts - any mention of low level wind shear (LLWS) or the possibility of severe thunderstorms, heavy rain showers, hail, and wind gusts suggest the potential for LLWS and microbursts. b. METARS - inspect for any indication of thunderstorms, rain showers, or blowing dust. Additional signs such as warming trends, gusty winds, cumulonimbus clouds, etc., should be noted. c. Severe weather watch reports, SIGMETs, and convective SIGMETs - severe convective weather is a prime source for wind shear and microbursts. d. LLWAS (low level windshear alert system) reports - installed at 110 airports in the U.S.; 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 of wind shear.