WEATHER INFORMATION

Current and forecast weather information are used to help Flight Dispatcher and flight crews to formulate plans, help whether to proceed with, delay or cancel a flight, reroute or make other plans for safe and economical operations. Tracking of weather disturbances and monitoring volcanic activities that may affect the safety of the flights is also part of the aviation weather services.

Flight documentation including weather information is required for each flight. The documentation must cover the flight in respect of time, altitude and geographical extent including the route between destination and destination alternate .

Presentation may vary according to regional agreements and standards. Flight documentation must be supplied (or updated in case of delay) as close to departure as practicable.

Standard flight weather documentation should contain:
• Significant Weather Chart (SIGWX) including wind forces (jet streams) and tropopause heights;
• Upper winds and temperature charts;
• Aerodrome forecasts, actual and special report (For example: RWY report):
       - For aerodrome of departure, take-off alternate if required, destination and destination alternates;
       - For flights of more than 2 hours the forecast must cover en-route alternates;
• Information of specified en-route weather phenomena (SIGMET); information concerning volcanic ash clouds and tropical cyclones must be based on advisory information provided by Volcanic Ash Advisory Centers (VAACs) and Tropical Cyclone Advisory Centers (TCACs);
• Low Level en-route weather (AIRMET) – as applicable.

In out stations this information (in printed or other officially approved form) should be provided by authorized handling agents. Flight Dispatcher on duty shall closely monitor the weather using TAFs, particularly on longer flights considering that the accuracy of forecasts degrades with time. On short flights, dispatchers shall supplement their evaluation with METARs and SPECIs. Peculiarities of airports such as terrain, inherent weather such as fog, crosswinds, windshear, temperature inversion, etc., should be taken into consideration.

Issue and valid time of aerodrome forecast and reports are according to World Meteorological Organization (WMO) / ICAO codes and schedule. Refer to Jeppesen General Part – Meteorology.

TAF refers to Terminal Aerodrome Forecast issued by Meteorological offices of States. The period of validity should not be less than 6 hours and no more than 30 hours. TAFs valid for less than 12 hours should be issued every 3 hours and those valid for 12 to 30 hours every 6 hours. Notice that the issuance of the forecasts is 2 hours prior to their effectively.

METAR is a Meteorological Aerodrome Report issued half hourly or hourly, e.g. 0920 / 0950, 1400 / 1430, or 1600 / 1700, by the MET office. METAR values are mean 10-minute values, or values averaged over a period of 10 minutes.

SPECI and Local Routine or Special Reports are issued where the meteorological conditions are reaching or passing through a specified threshold. SPECI are disseminated the same way as METAR. SPECI values are mean 2-minute values. Local routine/special report is sent to the local ATC and Airline Operators and other users of the aerodrome.

Aerodrome Trend Forecasts shall indicate significant changes in weather elements and be appended to METAR or SPECI. When no change is expected to occur, the term NOSIG should be used, representing no significant changes in wind/VIS/weather type/clouds. The Trend Forecast shall begin with the change indicators BECMG (becoming), TEMPO (temporary) or PROB (probability percentage). The period during which, or the time at which, the change is forecast to occur shall be indicated by FM (from), TL (until) or AT (at) followed by the time group in hour and minute. The period of validity is normally 2 hours from the nominal observation time of the report to which the TREND is appended.

Flight Dispatcher shall also take into consideration the destination and alternate minima as published on Jeppesen charts or as determined by the Company, alongside the forecast values, in order to visualize the proximity between such values and the amount of deterioration the forecast values may have, before such forecast values can be declared suitable or unsuitable for current operations.