Weather Forecasts and Reports

The primary method of preflight meteorologic briefing for aircrew in most parts of the aviation world is self-briefing. This is done in one of two ways:

1. Using facilities, information, and documentation routinely available or displayed in aerodrome briefing areas. Note: Computerized systems providing specific route meteorologic conditions are commonplace in most of the major airports around the world.

2. Using a telephone service to call an aviation authority met office; e.g., area forecasts (TAFS) or reports (METARS) are available directly from a meteorologic officer, and/or area forecasts are available from an airmet telephone recording system, especially in the United Kingdom.

What is an AIRMET?

An AIRMET is a recorded telephone message that gives the meteorologic forecast for a particular area. It can be accessed by area, and telephone numbers for different areas are listed on an AIRMET Areas Chart.

What is a meteorologic report?

A meteorologic report is an observation of the actual weather at a specific time, i.e., either past or present.

Common aviation meteorologic reports

The common aviation meteorologic reports are

1. METARS, SIGMETS, and SPECI

2. Automatic Terminal Information Service (ATIS)

3. In-flight weather reports (i.e., Volmets, ATIS, and by radio communications with an air traffic service unit or flight information service)

What are METARs?

A Meteorological Terminal Air Report (METAR) is a written, coded routine aviation weather report for an aerodrome. It is an observation of the actual weather given by a meteorologic observer at the aerodrome.

Note: Cloud base in a metar is given above ground level (AGL).

Decode the following METAR: METAR: EGCC/0920Z/210/15 G27/1000 SW/R24/P1500M/SHRA/BKN 025 CB/08/06/Q1013 or 29.92/RE TS/WS TK OF RWY 24/NOSIG.

EGCC Location identifier (Manchester, U.K.) 0920Z Time the report was taken (09.20 hours UTC) 210/15 G27 Wind direction and speed (210 degrees true at 15 knots, gusting to 27) 1000 SW Horizontal visibility (1000 m to the southwest) R24/P1500m Runway visual range (runway 24 plus 1500 m of visibility) SHRA Weather (rain showers) BKN 025 CB Clouds (broken at 2500 ft with cumulonimbus clouds) 08/06 Temperature/dewpoint (8°C temperature, 6°C dewpoint) Q1013 or 29.92 QNH (1013 millibars or 29.92 in) RE TS Recent weather (recent thunderstorms) WS TK OF Windshear (windshear report on takeoff runway 24) RWY 24 NOSIG Trend (no significant change)

What does trend mean in a meteorologic report?

A weather trend is usually attached to an aerodrome weather report, i.e., METAR, and is commonly referred to as a landing forecast. The trend is a forecast of any significant weather changes expected in the next 2 hours after the time of the report and is described using the normal coded weather format and abbreviations. If no significant change is expected, the observation (report) will be followed by NOSIG (no significant change) as the trend. Because a trend forecast period is much shorter than a normal aerodrome forecast; i.e., a TAF, it should be much more accurate.

Note: Cloud bases in a trend are given above aerodrome level (AAL). A trend can only be given by a qualified forecaster, whereas a report can be given by just an observer.

What is a SIGMET?

A SIGMET is a meteorologic report that advises of significant meteorologic (SIG/MET) conditions that may affect the safety of flight operations in a general geographic area, i.e., en route or at an aerodrome. The criteria for raising a SIGMET include

1. Active thunderstorms

2. Tropical revolving storms

3. Severe line squalls

4. Heavy rain

5. Severe turbulence

6. Severe airframe icing

7. Marked mountain waves

8. Widespread dust or sandstorms

What are SPECIs?

A SPECI is an Aviation Selected Special Weather Report for an aerodrome. It is generated whenever a critical meteorologic condition exists, e.g., windshear, microbursts, etc. It is similar in presentation to a METAR.

What in-flight weather reports can you access?

In-flight weather reports that can be accessed include

1. Flight information service or air traffic (control) service

2. ATIS

3. VOLMET

What is ATIS?

The Automatic Terminal Information Service (ATIS) is a prerecorded tape broadcast on an appropriate VOR or VHF channel to reduce the workload on air traffic control (ATC) communications frequencies that give current information on aerodrome operations and weather.

Note: Some of the larger aerodromes have both an arrival and a departure ATIS. The ATIS message is changed with any significant change in the reported conditions, and each new message has a new alphabetical designator prefix, e.g., alpha, beta, etc., to distinguish the current from the old.

What is VOLMET?

VOLMET is a continuous broadcast on a VHF/HF frequency that includes

1. The actual weather report

2. The landing forecast

3. A forecast trend for the 2 hours following

4. A SIGMET (significant weather, if any) of several selected aerodromes that produce meteorologic reports within a given region.

What is a meteorologic forecast?

A forecast is a prediction, or prognosis, of what the weather is likely to be for a given route, area, or aerodrome.

What are the common types of aviation forecasts?

The common types of aviation forecasts are

1. Area forecasts for preflight briefings (Note that cloud bases in area forecasts are given above mean sea level.)

2. Aerodrome forecasts (e.g., TAFS and trends)

3. Special forecasts

What is a TAF?

A Terminal Aerodrome Forecast (TAF) is a coded routine weather forecast for an aerodrome. It is a weather forecast given by a qualified meteorologic forecaster based at the aerodrome.

Note: Cloud base in a TAF is given above aerodrome level (AAL). TAFs are usually issued for a 9-hour period and updated every 3 hours. However, they may be issued for up to 24 hours with updates every 6 hours, but their accuracy is not as high.

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