Shannon VOLMET: aviation weather for the North Atlantic on 5505 kHz

What you hear

A calm, slightly mechanical woman's voice reading weather reports one after another, with no pause between them: "Dublin, at one two three zero, wind two four zero degrees one five knots, visibility one zero kilometres or more, few at two thousand feet, temperature one two, dew point zero eight, QNH one zero one two, no significant change." Then the next airport, then the next. Every few minutes the voice says "This is Shannon VOLMET" and starts the list again from the top. The order never changes and the tone never changes; only the numbers are refreshed, every half hour, as the airports publish new observations.

The reports are METARs, the standard airport observations, read in the ICAO phraseology that pilots learn in training. The list covers Ireland and Britain, the big hubs of western Europe and the airfields a crew would divert to on an Atlantic crossing. If you know the reading rules you can write each METAR down exactly as the airport issued it; if you do not, ten minutes of listening is enough to tell which airports have fog this morning and which have wind.

Who transmits and why

VOLMET is an old word made from the French "vol" (flight) and "météo" (weather). An aircraft far from any airport has no simple way to get the latest weather at its destination, and a continuous HF broadcast solves that for every aircraft at once: the crew tunes in, waits for its airport to come round in the cycle and writes the numbers down. Datalink has taken over much of this on modern airliners, but the voice broadcast stays on the air because HF needs nothing beyond a receiver, and because the oceanic airspace is large and not every aircraft crossing it is new.

Shannon VOLMET is run by the Irish Aviation Authority from the Shannon aeronautical radio station in County Clare, the same station that handles the HF voice traffic of the Shanwick oceanic area.

When and where to listen

The service uses four frequencies, all in upper sideband: 3413, 5505, 8957 and 13264 kHz. 5505 and 8957 kHz are listed as continuous; 3413 kHz is the night outlet and 13264 kHz the daytime one. 5505 kHz is the best place to start: from western and central Europe it is audible at almost any hour, strongest from late afternoon through the night, when the lower frequencies carry. In full daylight 8957 kHz is usually louder from far away, and 13264 kHz reaches furthest around midday.

The transmitter is on the west coast of Ireland, so receivers in Ireland and Britain hear it as a local signal. From Scandinavia, Germany, Poland and further east it arrives by skywave and fades gently in and out. Receivers on the east coast of North America can hear it at night too, which is the whole point of the service.

The mode in the catalogue is USB, and that is the right one: the transmitter sends a single sideband with no carrier, so AM would give you a hollow, muffled voice.

In ShackDeck

Station catalogue → Aviation → Shannon VOLMET. The program looks for a public receiver that covers 5505 kHz, tunes it and sets upper sideband; the voice starts within a few seconds. No receiver, antenna or account of your own is needed. If the hour is wrong for 5505, the daytime outlet has its own row, Shannon VOLMET (day) on 8957 kHz.