A subtle distinction young meteorologists of my generation were required to grasp was that between a cipher and a code.
The former, we were told, was used by spies, to exchange secret information in a form no one else could read. A message in code, on the other hand, although at first glance it might seem as indecipherable as any cipher, was intended to be understood by anyone, and its key, as a general rule, was readily to hand.
Typical of the latter, it was said, was the synoptic code as used by meteorologists. We saw an example of this yesterday in Weather Eye as a string of numbers arranged in groups of five, which describe the weather at a certain spot at an appointed time. It is called the synoptic code as it is used for transmitting reports of synoptic observations, i.e. weather observations all made at exactly the same time.
Meteorologists have other codes as well. The Metar code, for instance, is used to give weather information to a pilot. The acronym stands for Meteorological Aviation Report, which provides a description of the weather at a particular airport at a certain time. A typical example might be: METAR EIDW 1000Z 31015G27KT 3000 RA SCT008 OVC030 12/ 11 Q1014.
Roughly decoded, it reads: "At Dublin Airport at 10 o'clock GMT there was a fresh north-westerly wind, gusting occasionally to 27 knots; the visibility was 3 kilometres in rain; there were scraps of cloud 800 ft above the ground, and the sky was overcast at a height of 3000 ft; the temperature was 12C, the dew point - a measure of the humidity - was 11 degrees, and the pressure altimeter setting for an aircraft landing at Dublin Airport is 1014 hectopascals."
The TAF is another case in point. A Terminal Aerodrome Forecast gives a prediction of weather conditions expected at a certain airport in the future, and has the form TAF ESSB 0915 18007KT 1200 RA OVC004 BECMG 1012 7000 BR BKN012.
This is a forecast for Stockholm Airport for the period 0900 to 1500 GMT on the day in question. It predicts a southerly wind of seven knots, 1,200 metres visibility in rain, and a sky overcast with cloud at 400 ft above the ground. But the portion beginning BECMG 1012 brings good news: the letters mean "becoming", and the last groups predict that between 1000 and 1200 GMT the visibility will improve to 7 km in mist, and there will be only broken cloud 1,200 ft above the ground.