Ten aeroplanes will take to the skies, equipped with cloud-seeding agents in an attempt to induce rain away from the city, allowing holidaymakers and visiting heads of state to enjoy dry weather below.

Celebrations of the anniversary of Russia’s historic capital and seat of imperial government a week today will be attended by hundreds of thousands of visitors. A weekend of festivities will be attended by President Putin, President Bush, Tony Blair and the leaders of other EU nations.

Vladimir Stepanenko, head physicist of St Petersburg’s Geophysics Observatory, said: “Our aim is to empty all clouds of rain before they hit the city borders.” Such practice may strike awe into the heart of every rain-soaked Brit, but Russians take “cloud-bursting” for granted, having enjoyed its benefits over public holidays since Stalin gave the order to research weather control in the 1930s.

Over decades, the observatory in St Petersburg has developed techniques to dispel clouds, divert hailstorms from harvests, arrest avalanches, disperse fogs from airports and bring rain to drought-afflicted regions.

The most reliable form of rain prevention is to induce the clouds to rain before they float over the area under protection. The pilots on board the cloud-bursters will be directed towards rainclouds by meteorologists on the ground. On the orders of geophysicists on board the aircraft, dry ice will be dispensed into the clouds from a mile away. The dry ice is fired in special pyrotechnic capsules that combust once empty. Once injected with dry ice, rain crystalises within the cloud and falls ten or fifteen minutes later.

Approximately one kilogram of dry ice is used for every square kilometre of rain cloud. Rainclouds will be burst at a safe distance of 30 miles (50km) outside the city, where locals, used to sudden rain on fine days, will have their umbrellas ready. But thunderclouds are feared because pilots are by law forbidden to fly within more than seven miles of them, making it impossible to seed them with raininducing agents. The aircraft will patrol the skies until the end of the summit on May 31.

Russia’s first private weather controlling agency, the Atmosphere Technologies Agency, will be taking part in the delicate operation. It is hoping for rainclouds. “No rainclouds equals no pay,” Viktor Petrov, the deputy director, said.

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