10.2.2: Meteorological Services (MET)

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Meteorological service for international aviation is provided by meteorological authorities designated by states through the use of standardized MET products and services delivered in accordance with ICAO Annex 3 regulations. Each State also establishes a suitable number of meteorological offices, i.e. aerodrome meteorological offices, meteorological watch offices (MWOs) and aeronautical meteorological stations. Those services have been established on the prevailing state-of-the-art available in the 1960’s, and consist mainly in coded information, which is composed of:

METAR/TAF: Aerodrome MET conditions/forecast;
SIGMET: En-route significant weather advisory;
AIRMET/GAMET: En-route weather phenomena (less significant).

Moreover, weather forecasts (including wind and convective areas, both very relevant) of en-route conditions, except forecasts for low-level flights issued by meteorological offices, are prepared by world area forecast centres (WAFCs). This ensures the provision of high-quality and uniform forecasts for flight planning and flight operations.

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Figure 10.5: Meteorological effects.

Figure 10.5 presents a Cumulonimbus: a highly convective region that should be avoided when encountered. On the right-hand side, winds over the North-Atlantic region are presented, where a Jet Stream⁶ can be seen. Airlines would plan its flight plane taking advantage of favourable winds. In the Figure, the Great-Circle Distance (also referred to as orthodromic or minimum distance path) is compared with wind optimal trajectories. The difference is significative. Indeed, anyone who would have flown over the North Atlantic would have noticed that flying eastwards is much faster than flying westwards. The main reason is the Jet Stream.

6. Jet Stream refers to fast flowing, narrow air currents found in the upper atmosphere or in troposphere of Earth. There is typically one in the North Atlantic.