As good as it gets

Nobody's perfect, not even the men and women who forecast theweather, writes Brendan McWilliams

Nobody's perfect, not even the men and women who forecast theweather, writes Brendan McWilliams

Meteorologists are not infallible, as yet. Even when making solemn proclamations to the world on matters solely concerned with meteorology or climate, they do not deem themselves immune from error.

Perfection is a distant dream towards which they strive; meanwhile theirs is an art of the possible, and they are conscious of its limitations.

A number of factors place infallibility beyond their grasp. First of all, there are the uncertainties in assessing the state of the atmosphere at any time. The picture is built up from observations of temperature, pressure and humidity at places perhaps 100 miles apart - or, in some regions of the world, more than 10 times that distance.

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The forecaster's impression is more a Monet than a Caravaggio; the picture of the atmosphere has a certain fuzziness, and some grainy quirk may grow to catch one unawares.

There are also limits to our knowledge of the processes that shape the weather, and even more to the ways that have been devised to express these as mathematical equations. The formulae computers use to describe the behaviour of the atmosphere are not exact; they are approximations, and future developments as predicted by the computer may be underestimated or subject to exaggeration.

And even if the pressure pattern and positions of the fronts are pinpointed, further inexactitude can occur in deducing from these the amount and thickness of the cloud, the gustiness of the wind or the heaviness or persistence of the rain.

Situations prima facie very much alike often result in quite dissimilar weather conditions.

Added to these general problems are difficulties specifically related to forecasting the weather for Ireland. We live in a region of very changeable weather, so forecast conditions will almost invariably be very different from those being experienced; "persistence", a useful tool in very many countries, is of little use in a climate as volatile as ours.

We are disadvantaged, too, in being situated on the western edge of a continent. Most of our weather approaches over a vast expanse of ocean, from which comparatively few weather observations are available; it is all too easy for sudden, unobserved developments to take us unawares.

In recent years, as weather satellites have become more sophisticated in the amount, variety and quality of the information they provide, this disadvantage is less marked than was the case some years ago.

Nonetheless, life is easier for forecasters in Germany or on the east coast of the US, where approaching weather systems can be carefully and accurately tracked as they move eastwards across the dense network of observing stations lying upstream.

On the other hand, in their darker moments meteorologists glean courage from the fact that only very rarely is a forecast wrong in all respects; but then again, it is also seldom absolutely right.

The message consists of information on a wide range of elements, such as wind, temperature, rain and visibility; a forecast thought by one individual to have been good, because it was correct in the matters that concerned him, may well have been a failure to another who had different interests. The sailor, for example, may care little about the frosts that bother horticulturists, but it may be a matter of life and death to get a timely warning of a storm.

Forecasters have to learn to cope with this kaleidoscope of day-to-day uncertainty. One way of doing so is "hedging", a verbal technique whereby the presenter makes the forecast so woolly and ambiguous that nobody listening will know quite what it means. Needless to say, in the Republic this objectionable ploy is unknown; our meteorologists are internationally renowned for their predictive courage.

And through all the caveats and the occasional embarrassments, one beacon of encouragement shines brightly forth: all objective assessments indicate that the commonly perceived improvement in the quality of weather forecasts in recent years is not illusory. Meteorologists are far from being infallible, but they are much less prone to error than they used to be.

Brendan McWilliams is a former deputy director of Met Éireann and has written the Weather Eye column in The Irish Times for 14 years. He is administrative director of Eumetsat, the European Organisation for the Exploitation of Meteorological Satellites, in Darmstadt, Germany