At last good news — after the threatened flu pandemic, credit crunch and global recession, this summer in Britain could be warm and dry. According to Met Office chief meteorologist Ewen McCallum, it is “odds-on for a barbecue summer, and we can expect times when temperatures will be above 30C. Last year we had only one day of that temperature.”

The chances are better than 50 per cent that temperatures will be above Britain’s summer average of 14.1C (57.4F), while rainfall will be near or below normal. After the dreadful summers of the past two years, with floods, clouds and cool winds, that opens the way to a boost for domestic tourism. A holiday at home in these tough times may pay off in more ways than one, because temperatures across the Mediterranean are not expected to rise above their average.

Already the first signs of decent weather may be on the way, as this Bank Holiday weekend is expected to be reasonably warm, sunny and dry, at least for the southern half of Britain, as high pressure pushes up from the warm Azores.

But long-range forecasts need to be treated with caution. “We’re trying to give a measured view, based on probabilities,” Dr McCallum said. That means there could be hiccups, such as showers stopping play at Wimbledon (except for the new covered Centre Court), giving mudbaths at Glastonbury, or ruining Test matches.

“Seasonal predictions also cannot pinpoint extreme events. No one quite realised how abysmal the intense summer downpours of 2007 and 2008 were going to be, although heavier than average rainfall was forecast.”

And this winter was expected to turn warm at the end. Instead, February was freezing cold and Britain had its worst snow for 18 years.

Even vague predictions have huge pay-offs, however. “It helps key areas, especially government departments, utilities, infrastructure and retail markets,” said Pat Boyle, public weather service manager at the Met Office. “UK tourism suffered two miserable summers and agriculture had to put up with things like potato blight from the heavy rains.”

Supermarket chains and department stores use long-range forecasts to help to plan their stocks. Tesco recently appointed six data experts to advise on how to turn weather information into stocks on shelves. They found, for instance, that meat sales rise three times for each 10C rise in temperature because more people have barbecues, while beer sales rise 10 per cent for every 3C rise.

Other supermarket chains have discovered that sales of fizzy drinks soar, but at about 23C (73F) bottled water sales rise instead. In hot weather, sherry becomes less popular but white wine sales shoot up, chicken sandwiches are preferred to cold beef ones and we drink more tea than coffee. The biggest effect of hot weather is on sales of leg wax, which rise some 14-fold, closely followed by hair removal cream.

In cold winter weather, Tesco reports its greatest surge in sales is in cat litter — “people use it as gritter”.