Meteorological Information for Aircraft in Flight — Page 541, Lesson 518

I want to walk you through the VOLMET system — a key source of in-flight meteorological information for pilots operating under professional standards. VOLMET is a service where individual stations, in each region, broadcast weather reports and forecasts for a group of major aerodromes in their region of responsibility. So each VOLMET station is responsible for covering a specific set of airfields. Let's look at the UK as an example. From the figure I have here, you can see there are four UK VOLMET stations: LONDON VOLMET MAIN, LONDON VOLMET NORTH, LONDON VOLMET SOUTH, and the SCOTTISH VOLMET. Next to each station, the figure shows the frequency on which the VOLMET transmission is broadcast, the operating hours, and the list of aerodromes covered by that broadcast. Take LONDON VOLMET MAIN as an example. It is transmitted on the VHF frequency of 135.375 MHz, and it operates continuously over a 24-hour period. So you can tune in at any time, day or night. Now, the content of each VOLMET broadcast is a set of pre-recorded weather elements. These broadcasts are updated every half hour. So every thirty minutes, the recorded message is refreshed with the latest observations and forecasts. You'll also notice from the figure that LONDON VOLMET MAIN doesn't just cover UK aerodromes — it contains weather information for aerodromes in France and the Republic of Ireland as well. LONDON VOLMET SOUTH, on the other hand, covers major airfields between Birmingham, in the Midlands, and the island of Jersey, in the English Channel. So each station has a defined geographic scope. Column 6 of the figure details the specific weather elements included in the VOLMET broadcasts. The broadcast content has the same format as that of a METAR — that's the routine aerodrome weather report. However, in the examples of actual VOLMET broadcasts, you'll notice that TAF-terminology is also used. TAF stands for Terminal Aerodrome Forecast, and terms like BECMG and TEMPO appear. BECMG means 'becoming' — indicating a change to a new condition. TEMPO means 'temporarily' — indicating a temporary fluctuation. So the VOLMET broadcast has a forecast element as well, not just current observations. Let me walk you through a sample LONDON VOLMET MAIN broadcast so you can see exactly how this information is presented. I'll read the Amsterdam report as an example. It begins with the station identification: "THIS IS LONDON VOLMET MAIN." Then for Amsterdam, the time of the observation is given: "AMSTERDAM AT 1125" — that's 1125 UTC. Then the wind: "WIND 160 DEGREES 16 KNOTS, VARIABLE BETWEEN 130 AND 190 DEGREES." So the wind direction is 160 degrees true, speed 16 knots, and it's varying between 130 and 190 degrees. Visibility: "VISIBILITY 7 KILOMETRES." Then weather: "LIGHT RAIN SHOWERS." Cloud: "CLOUD FEW 2 THOUSAND FEET, FEW CUMULONIMBUS 2 THOUSAND 5 HUNDRED FEET, BROKEN 4 THOUSAND FEET." So there are a few clouds at 2000 feet, a few cumulonimbus clouds at 2500 feet — cumulonimbus is important because it indicates thunderstorm potential — and a broken layer at 4000 feet. Temperature and dew point: "TEMPERATURE 14 DEW POINT 9." So the temperature is 14 degrees Celsius, and the dew point is 9 degrees Celsius. QNH: "QNH 1004" — that's the pressure setting to get altitude above mean sea level, in hectopascals. Then the forecast element: "BECOMING, VISIBILITY 10 KILOMETRES OR MORE, NIL SIGNIFICANT WEATHER." So the conditions are expected to improve to 10 kilometres or more visibility with no significant weather. Now compare that to the Brussels report. Brussels at 1120: wind 190 degrees 14 knots, maximum 24 knots — so they give a maximum gust. Visibility 10 kilometres or more, light rain showers. Cloud scattered at 2300 feet, scattered at 5000 feet, broken at 10000 feet. Temperature 13, dew point 10, QNH 1006. And at the end: "NOSIG" — that means no significant change is expected. Glasgow at 1120: wind 070 degrees 5 knots, variable between 030 and 110 degrees. Visibility 10 kilometres or more. Cloud few at 1800 feet, scattered at 4500 feet. Temperature 14, dew point 8, QNH 997. Dublin at 1130: wind 260 degrees 6 knots, variable between 240 and 300 degrees. Visibility 10 kilometres or more. Cloud scattered at 2400 feet, scattered at 20000 feet. Temperature 13, dew point 6, QNH 997. And again, NOSIG. So the key takeaway is that VOLMET gives you, in a single voice broadcast, the current METAR-style conditions plus a short forecast trend for major aerodromes along your route, updated every half hour. As a professional pilot, you'd tune to the appropriate VOLMET frequency for your region to get this information while in flight.