The television era began for meteorology in 1936 when the first weather maps appeared on BBC TV. An anonymous hand would point out the fronts and isobars on the hand-drawn chart, while a disembodied voice read the detailed forecast to the accompaniment of tasteful light music.
By the time Teilifis Eireann arrived in the early 1960s, however, the Irish forecaster was in full view, standing beside a pair of boards assembled like a sash window. The weather maps were drawn on the boards in felt-tipped pen. Having carefully explained the details of the "today" chart, the forecaster would "open the window", so to speak, on tomorrow's weather by pushing the first board up and out of view to expose the second to the camera.
Techniques in both countries have improved beyond recognition since then. Today's weather graphics for RTE and TV3, for example, are prepared by Met Eireann forecasters using a sophisticated suite of computer programs custom-designed by a Norwegian software company.
The weather charts displaying the pressure patterns for specified times are loaded directly from Met Eireann's numerical weather prediction models, and are altered automatically by the system to fit the exact scale, projection and area of coverage of the background map being used.
The forecaster, however, has an editing facility which allows the image to be altered if need be. This may be done for aesthetic reasons (to make the pattern easier for the viewer to assimilate) or perhaps because later information is available to the forecaster than may be known to the computer.
As well as isobars and fronts, the forecaster can also call up observed or forecast rainfall and temperature patterns; spot values of these elements derived from observations; graphic illustrations of the likely wind flow, and movie-like multi-coloured sequences of satellite and weather radar images. All these individual frames are assembled in creative combinations to suit the current weather narrative, providing a vivid display to capture the characteristic volatility in both space and time of likely meteorological developments over the period of interest.
When the forecast goes on air, this pre-packaged weather movie is drawn directly from the graphics computer and combined electronically with the image of the forecaster on camera. This means, of course, that the chart which appears to be behind the presenter does not, in fact, exist at all. When the person on screen indicates a deep depression over Dingle, he or she is really pointing at a silver backdrop which stays blank throughout. Imagination and experience suggest the appropriate place to indicate, and a surreptitious glance at an adjacent TV monitor confirms if this is right.