Banish all thoughts of Michael Fish casting the runes or staring into a crystal ball. Weather forecasters are using satellite data to compile sales projections for companies including Sainsbury, Marks & Spencer and Cadbury Schweppes. The Met Office, part of the Ministry of Defence, must become self-financing by April. It has always offered a weather service for farmers and the oil industry; now it hopes to cash in on growing competition in Britain's high streets to cover its pounds 150m a year running costs.
"The weather throughout 1995 caused many retailers a lot of problems," says Clive Vaughan, retail consultant at Verdict Retail Analysis. "The hot summer kept shoppers away and the mild autumn debilitated warmer clothes sales."
Small wonder, then, if the Met Office has identified this as a new and lucrative market. "A broad range of goods and services are weather-sensitive - from car parts to hospital beds," says Vivienne Ballentine, managing director of Met Office division The Weather Initiative, which has quietly been developing its weather forecasting business since 1991. "We can predict demand for both, reducing forecast error by 50 per cent."
Most companies plan how many products they make and sell according to what happened at the same time last year. "But follow this line of thought and you'd expect demand for winter boots and fruit in November 1993 - one of the coldest on record - to match demand in November 1994, one of the warmest," says Ballentine. But it didn't.
Weather has a particular impact on what food we buy, adds Ballantine. And it's more than a matter of soups when it's cold, salads when it's not: "Eighty-four per cent of the variations in bread sales are due to the weather." But changes in demand can also be more subtle: "In the summer we buy more rolls, in the winter more loaves."
Failure to predict sudden temperature changes can leave many caught short. A sudden cold snap means shops are left with unwanted perishables - such as fruit and sandwiches. "A supermarket chain can lose pounds 90,000 a week on unsold sandwiches," Ballentine says.
According to Britvic's Mary Sweeting, short-term reports can be useful. "We look at temperature forecasts and humidity: it doesn't have to be sunny to make people feel thirstier." Anecdotal evidence proves the point. With most of the country experiencing a damp, dreary spell, thoughts are turning to the comfort of retail therapy. "Dull weather makes me want to buy things for my home - to make it cosier," says Marion Davies, 63. "A new lipstick or a glossy magazine can be uplifting. Or anything yellow. And when it's hot - nice china, something green. Things with leaves."
Helen Rose, 32, an air stewardess, adds: "When it's cold and really wet I see many more films." Hardly a coincidence, then, that over the grey, wet weekend before last (January 6) British cinemas reported that box-office takings soared to an all-time high of pounds 7.2m.
"White goods, consumer durables and even financial services are just as weather-sensitive," Ballantine adds. "Sales of tumble driers rise when it's wet, and fridges and freezers when it's hot and they're working overtime so need replacing."
The Met Office is now developing seasonal forecasts: it can predict the weather up to 30 days ahead. Retailers are enthusiastic, if sceptical. "The good old Met Office has had its share of mistakes - remember their failure to predict the big storm of '87? We're happy to use their short- term predictions along with other forecasting but wouldn't make business predictions solely on the weather," says a spokeswoman for Sainsbury.
Even so, the extremes of weather of recent weeks have done wonders for business, Ballantine says. And with growing pressure to become more commercial, the Met Office promises other weather initiatives: It's already planning Met Office merchandise - such as official paint, umbrellas and raincoats.
Whatever next? With the weather forecasters' star firmly in the ascendant, watch out as Messrs Fish, Giles and McGaskill take centre stage - perhaps advising the Royal family on when to schedule that Royal wedding. Or forecasting the best time for financial dealings in the City. Mystic Meg must be quaking in her boots.