Let’s start at the very beginning of this chapter — Page 473, Lesson 440

Let’s start at the very beginning of this chapter. I’m going to teach you about Meteorological Aerodrome Reports, which are universally known by their acronym METAR. The letters stand for METeorological Aerodrome Report. A METAR is a coded message that tells you the actual weather conditions at a specific aerodrome at a specific time. These are not forecasts — they are reports of what is happening right now, or was happening at the time the report was issued. METARs are usually issued every half hour during the aerodrome’s operating hours. So if an airport is open, you can expect a fresh METAR every thirty minutes. The aim of this chapter is to explain the METAR coding, group by group — we will decode each part of the message in order. Let me show you a typical example. Here is a METAR broken into its first eight code groups: METAR EGTK 231020Z 26012G25KT 220V300 I’ll label each part from (a) to (h) for clarity: - (a) METAR — this is the report type identifier. It tells you this is a routine METAR. - (b) EGTK — this is the four-letter ICAO designator of the aerodrome issuing the report. In this case, EGTK is Oxford/Kidlington airport. - (c) 231020Z — this is the date and time of the observation. The first two digits, 23, are the day of the month. The next four digits, 1020, are the time in hours and minutes UTC — that’s 10:20 UTC. The letter Z at the end stands for Zulu time, which is the same as UTC. - (d) 260 — this is the wind direction in degrees true. Here, 260 means the wind is coming from 260 degrees, which is roughly west. - (e) 12 — this is the mean wind speed in knots. So the average wind speed is 12 knots. - (f) G25KT — the letter G stands for gust. The number 25 is the maximum gust speed, also in knots. So we have gusts up to 25 knots. - (g) 220V300 — the letter V stands for variable. This shows the range of wind direction variation. Here, the wind direction is varying between 220 degrees and 300 degrees. - (h) 300 — this is the end of the wind group, showing the upper limit of the variable direction. So, putting it all together: this METAR says that at Oxford/Kidlington on the 23rd day of the month at 10:20 UTC, the wind is from 260 degrees at 12 knots, gusting to 25 knots, and the wind direction is varying between 220 and 300 degrees. Now, I want you to notice the structure. The first code group is always the report type — METAR. The second is always the four-letter ICAO aerodrome code. Then comes the date/time group, then the wind group. We will go through each group in detail as the chapter progresses. Let’s also look at some real examples from United Kingdom aerodromes, taken from the UK Met Office website. Here is one: METAR EGHD 031420Z 00000KT 9999 SCT025 13/08 Q1032= This says: at EGHD (which is Plymouth City Airport), on the 3rd day of the month at 14:20 UTC, the wind is calm — 00000KT means zero knots. Visibility is 9999, which is the code for 10 kilometres or more — that’s the maximum coded visibility. Then SCT025 means scattered clouds at 2,500 feet above aerodrome level. The temperature is 13 degrees Celsius, and the dew point is 8 degrees Celsius. Q1032 is the QNH, the atmospheric pressure adjusted to mean sea level, in hectopascals — here 1032 hPa. The equals sign at the end marks the end of the message. Another example: METAR EGHK 031420Z 34005KT 9999 SCT020 BKN040 15/08 Q1031 NOSIG= This is for EGHK, which is Glasgow Prestwick. Wind is from 340 degrees at 5 knots. Visibility 10 km or more. There are scattered clouds at 2,000 feet and a broken layer at 4,000 feet. Temperature 15°C, dew point 8°C, QNH 1031 hPa. The code NOSIG means no significant change is expected in the next two hours. Notice that some METARs end with NIL instead of a full report. For example: METAR EGDG NIL= and METAR EGHE NIL=. NIL means that no report is available — perhaps the aerodrome is closed or the observation equipment is not operating. Also note the format of the bulletin header above the METARs — lines like ZCZC ZKA498 031428 and SAUK34 EGYY 031420 — these are part of the data transmission system and are not part of the METAR itself. The actual METAR begins with the word METAR. Now, let’s look at the first eight code groups in our example again, because this is the standard skeleton of a METAR: 1. Report type (METAR) 2. Aerodrome ICAO code (EGTK) 3. Date and time (231020Z) 4. Wind direction (260) 5. Wind speed (12) 6. Gust indicator and speed (G25KT) 7. Variable wind direction lower limit (220) 8. Variable wind direction upper limit (300) We will build on this structure as we go through the rest of the chapter. For now, make sure you understand that a METAR is a coded, half-hourly report of actual weather at an aerodrome, and that each group of letters and numbers has a specific meaning that we will decode step by step.