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Five Mile Final | A Flight Instructor's Sandbox

Pilot's Handbook of Aeronautical Knowledge


Pilots must use several weather reports to get an overall picture of any weather that can affect the safe completion of a flight. Meteorologists have the ability to predict weather patterns, trends, and characteristics with increasing accuracy. Pilots and other aviation professionals benefit from a wide array of up-to-date weather reports and forecasts.


Observations

There are four types of weather observations: surface, upper air, radar, and satellite. These observations form the basis of all weather forecasts, advisories, and briefings.

Surface Aviation Weather Observations

METARs, or surface aviation weather observations, are compiled from individual ground stations across the United States. Information may be from a person, an automated station, or an automated station that is updated or enhanced by a weather observer. Automated weather sources contribute a substantial amount of data. These include Automated Weather Observing Systems (AWOS) and Automated Surface Observing Systems (ASOS).

Surface observations provide local weather conditions and other relevant information for a specific airport. This information includes:

Air Route Traffic Control Centers (ARTCC) maintain aircraft separation for IFR flights and provide traffic advisories for VFR flights. Air Route Surveillance Radar (ARSR) acquires and tracks transponder returns using the same basic technology as terminal radars. Using ARSR, controllers can provide weather insights. However, high-intensity weather makes it difficult for controllers to see aircraft data blocks. Pilots should not expect ATC to provide continuous weather information.

Upper Air Observations

A radiosonde is a small cubic instrumentation package that is suspended below a small balloon. As it ascends, it gathers data, including air temperature, moisture, pressure, wind speed, and wind direction. Data is relayed to ground stations via radio.

Pilot Reports (PIREPs) are in-flight upper air weather observations offered by pilots to ATC. They are the only real-time source of information regarding turbulence, icing, and cloud heights.

Many airlines have equipped their aircraft with instrumentation that automatically transmits in-flight weather observations through the DataLink system. The Aircraft Meteorological Data Relay system (AMDAR) is an international program utilizing commercial aircraft to provide automated weather observations, providing thousands of reports per day worldwide.

The Meteorological Data Collection and Reporting System (MDCRS) is an automated airborne weather observation program that is used in the United States. MDCRS collects and disseminates real-time upper-air weather observations from participating airlines.

Radar Observations

There are four types of radars which provide information about precipitation and wind.

WSR-88D NEXRAD radar, commonly called Doppler radar, provides in-depth observations that inform surrounding communities of impending weather.

Doppler radar has two operational modes: clear air and precipitation. In clear air mode, the antenna rotates more slowly compared to precipitation mode, with a longer time to sample the atmosphere, as well as a longer time delay between pictures (about 10 minutes, compared to 4-6 minutes in precipitation mode.)

Intensity values in both modes are measured in decibels of Z (dBZ) and are depicted in color on the radar image. ATC will refer to precipitation as "light," "moderate," "heavy," or "extreme" based on the dBZ measure.

Example of a weather radar scope.
WSR-88D Weather Radar Echo Intensity Legend.

Terminal Doppler Weather Radar (TDWR) is installed at some major airports around the country. TDWR provides severe weather alerts and warnings to ATC. Terminal radar ensures pilots are aware of wind shear, gust fronts, and heavy precipitation.

Airport Surveillance Radar is used primarily to detect aircraft. However, it also detects the location and intensity of precipitation. This can be used to route aircraft traffic around severe weather in an airport environment.

Airborne radar is carried by aircraft to locate weather disturbances. It is capable of penetrating heavy precipitation, which is necessary to determine the extent of thunderstorms. It also can detect less intense precipitation.

Satellite

Through the use of satellite subscription services, individuals are now able to receive satellite transmitted signals that provide near real- time weather information for the North American continent.


Service Outlets

Service outlets are government, government contract, or private facilities that provide aviation weather services.

The Flight Service Station (FSS) is the primary source for preflight weather information. A preflight weather briefing can be obtained by calling 1-800-WX BRIEF. Telephone numbers for Flight Service Stations also can be found in the Chart Supplement.

The FSS also provides inflight weather briefing services and weather advisories to flights within the FSS area of responsibility.

The Telephone Information Briefing Service (TIBS), provided by FSS, is a system of automated telephone recordings. TIBS provides area and route briefings, airspace procedures, and special announcements. It is designed to be a preliminary briefing tool and is not intended to replace a standard briefing from a FSS specialist. Phone numbers are listed in the Chart Supplement.

Transcribed Weather Broadcasts (TWEB) are only available in Alaska. They are continuous automated broadcasts of meteorological and aeronautical data over selected VOR navigational aids. Telephone numbers are found in the Alaska Chart Supplement.

The Hazardous Inflight Weather Advisory Service (HIWAS) was deactivated on January 8, 2020. It provided a broadcast of hazardous weather information over selected VOR navigational aids.


Weather Briefings

A weather briefing, obtained from a specialist at an FSS, can be provided in three formats: standard, abbreviated, or outlook. Briefers will need to know:

A standard briefing provides the most complete information. This type of briefing should be obtained prior to the departure of any flight and should be used during flight planning.

A standard briefing provides the following information:

An abbreviated briefing is a shortened version of the standard briefing. It should be requested when a departure has been delayed or when weather information is needed to update the previous briefing.

An outlook briefing should be requested when a planned departure is six (6) hours or more away. It provides initial forecast information that is limited in scope due to the time frame of the planned flight. This briefing can influence the route of flight, altitude, and the go/no-go decision. It should be followed by a standard briefing prior to departure.


Aviation Weather Reports

Aviation weather reports are designed to give accurate depictions of current weather conditions.

A METAR is an observation of current surface weather reported in a standard international format. The acronym stands for "Meteorological Terminal Aviation Routine" weather report. However, the Aeronautical Information Manual (AIM) refers to METAR as "Aviation Routine Weather Report."

A typical METAR report contains the following information in sequential order:

A routine METAR report is transmitted on a regular time interval. A SPECI can be given at any time to update the METAR for rapidly changing weather conditions, aircraft mishaps, or other critical information.

The station identifier is a four-letter code. In the 48 contiguous states, a three-letter identifier is preceded by the letter "K". Alaska identifiers begin with "PA". Hawaii identifiers begin with "PH".

Date and time is a six-digit group. The first two digits are the date. The last four digits are the time of the report, which is always in coordinated universal time (UTC), also referred to as "Zulu" time. A "Z" is appended to denote this.

The modifier denotes if the source is automated, or if the report has been corrected. "AUTO" the indicates that the report came from an automated source. "COR" identifies a corrected report that replaces an earlier report that contained an error. If the report is automated, the precipitation sensor type is designated by "AO1" or "AO2" in the "Remarks" section.

Wind is reported with five digits. The first three digits indicate the direction the true wind is blowing from in tens of degrees. The last two digits indicate wind velocity.

Prevailing visibility is reported in statute miles, denoted by the letters "SM". This can include fractions of miles. Runway Visual Range (RVR), also may be reported. This is the distance a pilot can see down the runway in a moving aircraft.

Weather includes qualifiers and weather phenomena. Qualifiers include intensity, proximity, and/or descriptors. Phenomena include precipitation, obscuration, or other types. The weather is then constructed in sequence — intensity, followed by descriptor, followed by weather phenomena — using symbols and abbreviations, per the following table:

Qualifier Weather Phenomena
Intensity or Proximity Descriptor Precipitation Obscuration Other
Light MI Shallow DZ Drizzle BR Mist PO Dust/sand whirls
Moderate (no qualifier) BC Patches RA Rain FG Fog SQ Squalls
+ Heavy DR Low drifting SN Snow FU Smoke FC Funnel cloud
VC in the vicinity BL Blowing SG Snow grains DU Dust +FC Tornado or waterspout
  SH Showers IC Ice crystals (diamond dust) SA Sand SS Sandstorm
  TS Thunderstorms PL Ice pellets HZ Haze DS Dust storm
  FZ Freezing GR Hail PY Spray  
  PR Partial GS Small hail or snow pellets VA Volcanic ash  
    UP *Unknown precipitation    

For example, heavy rain showers is coded as +SHRA. Light drizzle is –DZ.

Descriptions of weather phenomena as they begin or end and hailstone size are also listed in the "Remarks" sections of the report

Sky condition is reported as amount, height (AGL), and type. There also can be an indefinite ceiling/height. Vertical visibility may also be reported.

Air temperature and dew point are always given in degrees Celsius (C) or (18/17). Temperatures below 0°C are preceded by the letter "M" to indicate minus.

Altimeter setting is reported as inches of mercury as a four-digit number group always preceded by the letter "A". (e.g., A2992). Rising or falling pressure may be denoted in the Remarks sections as "PRESRR" or "PRESFR".

The Remarks section always begins with "RMK". Information may include wind data, variable visibility, beginning and ending times of particular phenomenon, pressure information, and anything deemed necessary.

Example METAR:

Hover over METAR to decode…

Pilot Weather Reports (PIREPs)

Pilot Weather Reports (PIREPs) provide observations as they actually exist. These observations cannot be gathered from any other source.

If the ceiling is below 5,000 feet, or visibility is at or below five miles, ATC facilities are required to solicit PIREPs from pilots in the area. Pilots are encouraged to make a report to an FSS or ATC when unexpected weather is encountered.

The elements of a PIREP form are shown in the associated table. Items 1-5 are required when making a report, in addition to at least one weather phenomenon. PIREPS are easily decoded, and most contractions used in the reports are self-explanatory

Encoding Pilot Weather Reports (PIREPS)
1 XXX 3-letter station identifier Nearest weather reporting location to the reported phenomenon
2 UA Routine PIREP, UUA-Urgent PIREP.  
3 /OV Location Use 3-letter NAVAID idents only.
  1. Fix: /OV ABC, /OV ABC 090025.
  2. Fix: /OV ABC 045020-DEF, /OV ABC-DEF-GHI
4 /TM Time 4 digits in UTC: /TM 0915.
5 /FL Altitude/flight level 3 digits for hundreds of feet. If not known, use UNKN: /FL095, /FL310, /FLUNKN.
6 /TP Type aircraft 4 digits maximum. If not known, use UNKN: /TP L329, /TP B727, /TP UNKN.
7 /SK Sky cover/cloud layers Describe as follows:
  1. Height of cloud base in hundreds of feet. If unknown, use UNKN.
  2. Cloud cover symbol.
  3. Height of cloud tops in hundreds of feet.
8 /WX Weather Flight visibility reported first:
Use standard weather symbols:
/WX FV02SM RA HZ, /WX FV01SM TSRA.
9 /TA Air temperature in celsius (C) If below zero, prefix with a hyphen: /TA 15, /TA M06.
10 /WV Wind Direction in degrees magnetic north and speed in six digits:
/WV270045KT, WV 280110KT.
11 /TB Turbulence Use standard contractions for intensity and type (use CAT or CHOP when appropriate).
Include altitude only if different from /FL, /TB EXTRM, /TB LGT-MOD BLO 090.
12 /IC Icing Describe using standard intensity and type contractions.
Include altitude only if different than /FL: /IC LGT-MOD RIME, /IC SEV CLR 028-045.
13 /RM Remarks Use free form to clarify the report and type hazardous elements first:
/RM LLWS -15KT SFC-030 DURC RY22 JFK.

Example PIREP:

Hover over PIREP to decode…


Aviation Forecasts

A variety of forecast products are used in preflight planning. Printed forecasts include the Terminal Aerodrome Forecast (TAF), Aviation Area Forecast (FA), Inflight Weather Advisories (SIGMET, AIRMET), and the Winds and Temperatures Aloft Forecast (FB).

Terminal Aerodrome Forecasts (TAF)

A Terminal Area Forecast (TAF) is established for the five statute mile radius around a large or busy airport.

Each TAF is valid for a 24 or 30-hour time period. It is updated four times a day at 0000Z, 0600Z, 1200Z, and 1800Z.

The TAF utilizes the same descriptors and abbreviations as used in the METAR report. The TAF includes the following information in sequential order.

  1. Type of report
  2. ICAO station identifier
  3. Date and time of origin
  4. Valid period dates and times
  5. Forecast wind
  6. Forecast visibility
  7. Forecast significant weather
  8. Forecast sky condition
  9. Forecast change group
  10. PROB30

A TAF can be either a routine forecast (TAF) or an amended forecast (TAF AMD).

The TAF valid period follows the date/time of forecast origin group. The first two digits are the day of the month for the start of the TAF, followed by two digits for the starting hour (UTC). A 12Z TAF issued on the 11th of the month and valid for 24 hours would have a valid period of 1112/1212. A 00Z TAF issued on the 9th of the month and valid for 24 hours would have a valid period of 0900/0924.

As with a METAR, the TAF forecast wind and speed forecast are coded in a five-digit number group. The wind direction is in reference to true north.

Forecast visibility is given in statute miles and may be in whole numbers or fractions. If the forecast visibility is greater than six miles, it is coded as "P6SM".

Forecast significant weather phenomena are coded in the TAF reports in the same format as the METAR.

Forecast sky condition is given in the same format as the METAR. Only cumulonimbus (CB) clouds are forecast in this portion of the TAF report. (METARs provide observations of both cumulonimbus and towering cumulus clouds).

If any significant weather change is forecast to occur during the TAF time period, the expected conditions and time period are included in the forecast change group. "FM" is used when a rapid and significant change, usually within an hour, is expected. "TEMPO" is used for temporary fluctuations of weather that expected to last less than one hour.

A given percentage that describes the probability of thunderstorms and precipitation occurring in the coming hours may be expressed with PROB with an associated percentage, e.g. "PROB30". This forecast is not used for the first six hours of the 24-hour forecast.

Example TAF:

Hover over METAR to decode…

Area Forecast (FA)

Area forecast region map.

An Area Forecast (FA) gives a picture of clouds, general weather conditions, and visual meteorological conditions (VMC) expected over a large area encompassing several states. Forecasts are published for six areas in the contiguous 48 states.

Area forecasts are issued three times a day and are valid for 18 hours.

Area forecasts provide vital information to en route operations. FAs also provide information for smaller airports that do not have Terminal Area Forecasts (TAFs).

When information is given in the area forecast, locations may be given by states, regions, or specific geological features such as mountain ranges.

Area forecasts are typically disseminated in four sections and include the following information:

  1. Header
  2. Precautionary statements
  3. Synopsis
  4. VFR Clouds and Weather

The header gives the location identifier of the source of the FA, the date and time of issuance, the valid forecast time, and the area of coverage.

Hover over Area Forecast (FA) to decode…

Precautionary statements include IFR conditions, mountain obscurations, and thunderstorm hazards. Heights are in MSL. If given otherwise, AGL or CIG (ceiling) is noted.

Hover over Area Forecast (FA) to decode…

The synopsis gives a brief summary identifying the location and movement of pressure systems, fronts, and circulation patterns.

Hover over Area Forecast (FA) to decode…

The VFR Clouds and Weather section lists expected sky conditions, visibility, and weather for the next 12 hours and an outlook for the following 6 hours.

Hover over Area Forecast (FA) to decode…

Inflight Weather Advisories

Inflight weather advisories, which are provided to en route aircraft, are forecasts that detail potentially hazardous weather. They also are available to pilots prior to departure for flight planning purposes. An inflight weather advisory is issued in the form of either an AIRMET, SIGMET, or convective SIGMET.

AIRMETs (WAs) are inflight weather advisories issued every six (6) hours, with intermediate updates issued as needed for a particular area forecast region.

The information contained in an AIRMET is of operational interest to all aircraft, but the weather section concerns phenomena considered potentially hazardous to light aircraft and aircraft with limited operational capabilities.

An AIRMET includes forecast of moderate icing, moderate turbulence, sustained surface winds of 30 knots or greater, widespread areas of ceilings less than 1,000 feet and/or visibilities less than three miles, and extensive mountain obscurement.

Each AIRMET bulletin has a fixed alphanumeric designator, numbered sequentially for easy identification, beginning with the first issuance of the day.

Hover over AIRMET to decode…

A SIGMET (WS) is an inflight advisory concerning non-convective weather that is potentially hazardous to all aircraft. This includes include severe icing, severe or extreme turbulence or clear air turbulence (CAT), dust storms or sandstorms that lower surface or inflight visibilities to below three miles, and volcanic ash. To be reported in a SIGMET, none of these phenomena would be associated with thunderstorms.

A SIGMET is issued under an alphabetic identifier, from November through Yankee. The first issuance of a SIGMET is designated as an Urgent Weather SIGMET (UWS). Reissued SIGMETs for the same weather phenomenon are sequentially numbered until the weather phenomenon ends.

Hover over SIGMET to decode…

A Convective SIGMET (WST) is an inflight weather advisory issued for hazardous convective weather that affects the safety of every flight. Convective SIGMETs are issued for severe thunderstorms with surface winds greater than 50 knots, hail at the surface greater than or equal to 3/4 inch in diameter, or tornadoes.

Convective SIGMETs also are issued to advise pilots of embedded thunderstorms, lines of thunderstorms, or thunderstorms with heavy or greater precipitation that affect 40 percent or more of a 3,000 square mile or greater region.

Convective SIGMETs are issued for the eastern (E), western (W), and central (C) United States, but not Alaska or Hawaii.

Each report is issued at 55 minutes past the hour, but special Convective SIGMETs can be issued during the interim for any reason. Each forecast is valid for 2 hours.

Convective SIGMETs are numbered sequentially each day from 1-99, beginning at 00Z time. If no hazardous weather exists, the convective SIGMET is issued with the statement "CONVECTIVE SIGMET...NONE".

Hover over Convective SIGMET to decode…

Winds and Temperature Aloft Forecast (FB)

Winds and Temperatures Aloft forecasts (FB) provide wind and temperature forecasts for specific locations throughout the United States, including network locations in Hawaii and Alaska.

FBs are made twice a day based on the radiosonde upper air observations taken at 0000Z and 1200Z.

Wind direction is always in reference to true north, and wind speed is given in knots. The temperature is given in degrees Celsius.

No winds are forecast when a given level is within 1,500 feet of the station elevation. Similarly, temperatures are not forecast for any station within 2,500 feet of the station elevation.

FB KWBC 151640
DATA BASED ON 151200Z
VALID 151800Z FOR USE 1400-2100Z
TEMPS NEGATIVE ABV 24000
FB 3000 6000 9000 12000 18000 24000 30000
AMA   2714 2725+00 2625-04 2531-15 2542-27 265842
DEN     2321-04 2532-08 2434-19 2441-31 235347


Weather Charts

Weather charts are graphic charts that depict current or forecast weather. They provide an overall picture of the United States, depicting the movement of major weather systems and fronts.

Surface analysis, weather depiction, and significant weather prognostic charts are sources of current weather information.

Surface analysis chart.

Surface Analysis Chart.

The surface analysis chart depicts an analysis of the current surface weather. A surface analysis chart shows the areas of high and low pressure, fronts, temperatures, dew points, wind directions and speeds, local weather, and visual obstructions.

The surface analysis chart is transmitted every three (3) hours and covers the contiguous 48 states and adjacent areas.

Surface weather observations for reporting points across the United States are also depicted on this chart. Each of these reporting points is illustrated by a station model, which includes:

Sample station model and weather chart symbols.

Weather Depiction Chart

A weather depiction chart details surface conditions as derived from METAR and other surface observations.

Weather depiction chart.

A bracket ( ] ) symbol to the right of the station indicates the observation was made by an automated station.

Significant Weather Prognostic Charts

Significant Weather Prognostic Charts are available for low-level significant weather from the surface to FL 240. It is a forecast of aviation weather hazards, primarily intended for briefing VFR pilots.

Each chart is divided on the left and right into 12 and 24 hour forecast intervals (based on the current NAM model available).

The two panels depict freezing levels, turbulence, and low cloud ceilings and/or restrictions to visibility (shown as contoured areas of MVFR and IFR conditions). These charts enable the pilot to pictorially evaluate existing and potential weather hazards they may encounter.


Commercial Pilot & Flight Instructor Test Questions

Which statement is true concerning ASOS/AWOS weather reporting systems? ASOS locations perform weather observing functions necessary to generate METAR reports.

Given: KOUN 151355Z AUTO 220110KT 10SM CLR BLO 120 13/10 A2993 RMK A02 $. The report indicates that the location is possibly in need of maintenance.
The dollar sign ($) indicates that the site may be in need of maintenance.

Given: KPNC 131215 AUTO 33025KT 1/2SM OVC005 00/M03 A2990 RMK A02 SLPNO. The report indicates that the sea level pressure is not available.
SLPNO indicates that the sea level pressure is not available.

Vertical visibility is shown on Terminal Aerodrome Forecasts (TAF) when the sky is obscured.

To determine the freezing level and areas of probable icing aloft, you should refer to an AIRMET or SIGMET.

An Aviation Area Forecast is valid for 12 hours with an additional 6 hours categorical outlook.

For a brief summary of the location and movement of fronts, pressure systems, and circulations patterns, the pilot should refer to an Aviation Area Forecast.

What is the meaning of MVFR, as used in the categorical outlook portion of an Aviation Area Forecast? A ceiling of 1,000 to 3,000 feet and/or visibility of 3 to 5 miles.

What information would be covered in an AIRMET? Extensive mountain obscurement.
"Severe turbulence" is a condition that would affect all aircraft, and thus would be included in a SIGMET, not an AIRMET. IFR operations are not affected by mountain obscurement.

Which in-flight advisory would contain information on severe icing? SIGMET.

What information is contained in a Convective SIGMET in the conterminous United States? Tornadoes, embedded thunderstorms, and hail 3/4 inch or greater in diameter.

The position of fronts and pressure systems (as of chart time) are best determined by referring to a Surface Analysis Chart.

The intensity trend of a front (as of chart time) is best determined by referring to a Surface Analysis Chart.
— "Trend" strongly suggests looking at a Prognostic Analysis Chart. In this case, the presence of "pips" on a front line indicate direction of movement.

On a Weather Depiction Chart, what weather conditions would be contained in an unshaded area that is enclosed by a smooth line? Ceiling between 1,000 and 3,000 feet and/or visibility between 3 and 5 miles.

A Weather Depiction Chart is useful to a pilot in determining areas where weather conditions were reported above or below VFR minimums.

What does the heavy dashed line that forms a rectangular box on the radar summary chart refer to? Severe Weather Watch Area.

A Radar Summary Chart can be very helpful to a pilot because it graphically displays the intensity and movement of precipitation.

Which weather chart depicts the conditions forecast to exist at a specific time in the future? Prognostic.

Regarding Convective Outlook Charts, when well-organized severe thunderstorms are expected but in small numbers and/or low coverage, the risk is referred to as SLGT.

How will an area of thunderstorm activity that may grow to severe intensity be indicated on the Severe Weather Outlook Chart? APCHG within any area.

If an area on a Convective Outlook Chart is labeled APCHG, this indicates winds greater than or equal to 35 knots but less than 50 knots.

Instrument Pilot Test Questions

During preflight preparation, weather report forecasts which are not routinely available at the local service outlet (AFSS) can best be obtained by means of contacting weather forecast office (WFO).

The Aviation Weather Center (AWC) prepares FA's for the contiguous U.S. three times each day.

Terminal Aerodrome Forecasts (TAF) are issued how many times a day and cover what period of time? Four times daily and are usually valid for a 24 hour period. There is not any type of categorical outlook.

Weather Advisory Broadcasts, including Severe Weather Forecast Alerts (AWW), Convective SIGMETs, and SIGMETs, are provided by ARTCCs on all frequencies, except emergency, when any part of the area described is within 150 miles of the airspace under their jurisdiction.

In-Flight Aviation Weather Advisories include what type of information? Forecasts for potentially hazardous flying conditions for enroute aircraft.

The Hazardous Inflight Weather Advisory Service (HIWAS) is a broadcast service over selected VORs that provides continuous broadcast of inflight weather advisories.

Which forecast provides specific information concerning expected sky cover, cloud tops, visibility, weather, and obstructions to vision in a route format? Transcribed Weather Broadcast.

To obtain a continuous transcribed weather briefing including winds aloft and route forecasts for a cross-country flight, a pilot could monitor a TWEB on a low-frequency and/or VOR receiver.

What is the upper limit of the Low Level Significant Weather Prognostic Chart? 24,000 feet.

Which provides a graphic display of both VFR and IFR weather? Weather Depiction Chart.

What flight planning information can a pilot derive from Constant Pressure Analysis Charts? Winds and temperatures aloft.

The minimum vertical wind shear value critical for probable moderate or greater turbulence is 6 knots per 1,000 feet..

What weather phenomenon is implied within an area enclosed by small scalloped lines on a U.S. High-Level Significant Weather Prognostic Chart? Cumulonimbus clouds, icing, and moderate or greater turbulence.

Which correctly describes the purpose of Convective SIGMET's (WST)? They consist of either an observation and a forecast or just a forecast for tornadoes, significant thunderstorm activity, or hail greater than or equal to 3/4 inch in diameter.

Which in-flight hazard is most commonly associated with warm fronts? Precipitation-induced fog.

When weather information indicates that abnormally high barometric pressure exists, or will be above 31.00 inches of mercury, flight operations will not be authorized contrary to the requirements published in NOTAMs.

The best product to provide an overview of forecast weather conditions creating a complete picture of weather affecting regions across the United States is Graphical Forecasts for Aviation (GFA).

What is the meaning of the terms PROB40 2102 +TSRA as used in a Terminal Aerodrome Forecasts (TAF)? Between 2100Z and 0200Z there is a forty percent (40%) probability of thunderstorms with heavy rain.

What is indicated by the following report? TYR UUA/OV TYR180015/TM 1757/FL310/TP B737/TB MOD-SEV CAT 350-390 An urgent pilot report for moderate to severe clear air turbulence.
— The UUA found in the first section of the report indicates an "Urgent Upper Air" report.

The distance measured in millibars separating isobars on surface analysis charts is typically 4 mb.

When using a Constant Pressure Analysis Chart for planning a flight at 10,000 feet MSL, a pilot should refer to the 700-millibar analysis.
— The 700-mb analysis corresponds to the 10,000-ft. pressure altitude. The 850-milibar analysis is equivalent to 5,000 feet MSL. The 500-milibar analysis is equivalent to 18,000 feet MSL.

(Figure) The cell is moving toward the southeast.
— A weather map with drawn circles around cells and a line indicates the area of the cell and its motion. The line is trailing. It is not an arrow.

Airborne weather radar is installed to help the pilot avoid severe weather.

Robert Wederquist   CP-ASEL - AGI - IGI
Commercial Pilot • Instrument Pilot
Advanced Ground Instructor • Instrument Ground Instructor