Weather: Do we really need the men from the Met Office?

Tomorrow's weather will be much the same as today's. So why do we bother with weather forecasters?

The dry, clear skies over the past week have rendered most short-term forecasts superfluous. The phrases "for the rest of this week" and "for the next few days" have cropped up regularly on radio and television forecasts, though they never seem to think of adding: "so we won't be giving you any more forecasts until Saturday, or until it starts raining, whichever comes first".

In fact, our weather is in general far more settled that we think. Just because rain always seems to take us by surprise, we tend to believe that the British weather is highly changeable. The figures show otherwise.

I have been looking at the temperatures and weather conditions as recorded in the weather pages of this newspaper throughout 1996, and they reveal a remarkable consistency. In London, there were only 86 days in the year when the temperature varied by more than two degrees from that of the day before. In Manchester the equivalent figure was 100 days. So the weather forecast "today will be much the same as yesterday" has a 77 per cent chance of being correct in London and 73 per cent in Manchester.

Of course that is cheating a little, because it takes account of only the temperature, not the overall weather, but the recorded conditions at noon each day in London and Manchester also follow some general rules: it's more likely to be cloudy than anything else; if it's sunny today, there is a good chance it will be sunny tomorrow too; and if it rained today, it will probably not rain tomorrow, though there is a good chance that it will rain the day after tomorrow (unless it rained the day before yesterday).

The table at the top of the next column gives the distribution of various types of weather in the two cities throughout 1996. The figures represent the percentage of days in which each type of weather occurred.

Sadly, they confirm the tale that Manchester is a rainy place, with less sun than London, though the capital does have more drizzle.

London Manchester

Cloudy 34.8 34.2

Sunny 21.0 16.3

Fair 19.7 19.7

Rain 8.2 12.2

Showers 6.1 9.5

Drizzle 4.3 2.4

Mist 2.0 1.0

Snow 2.0 1.7

Haze 1.7 0.3

Fog 0.3 1.7

Thunder 0.3 0.0

Sleet 0.0 1.0

The above table may, however, be perpetuating a myth about Mancunian weather, for it is possible either that 1996 was a particularly bad year for the north of England, or possibly that taking readings at noon works to Manchester's disadvantage. The figures quoted by Robin Stirling in The Weather of Britain led him to dismiss the concept of rainy Manchester as a fallacy. The average rainfall at Ringway airport is 819mm, which is distinctly less than that of Oldham (1142mm) or Rochdale (1130mm). Even Bournemouth has the same annual rainfall as Manchester, while Falmouth, Penzance and Ilfracombe have more.

"Statistics show that Manchester has rain on about 195 days a year on average," he says. "So do Southport and Falmouth." Mr Stirling blames cricket for Manchester's poor image: Old Trafford is simply the most westerly, and consequently the rainiest Test match ground. The average Manchester rainfall is in fact the same as the average for the country as a whole.

Having defended Manchester from the statistics, we are left with the problem of the weather forecasters. If, as we have seen, simply looking out of the window is a perfectly good way of forecasting tomorrow's weather, why do we in Britain bother with all those satellites, and tracking stations, and weather balloons, and high-speed computers, and the rest of the paraphernalia of modern state-of-the-art, no-hurricane-on-its-way-madam, forecasting?

The important question to ask is what the forecasters were saying on the eve of those 23 per cent of London days and 27 per cent of Manchester days when the temperature did change noticeably.

We shall see tomorrow how accurate they were at rising to those rather more testing challenges.