Much of the mainland might be in the grip of a crippling cold spell but weather experts yesterday forecast clear skies and a rain-free Olympics in seven months' time. Top officials of the Beijing Meteorological Bureau confirmed that cloud-seeding would be used to guarantee the opening ceremony would not be washed out. The Games are being staged during the capital's rainy season. 'Rain mitigation, using either silver dioxide or liquid nitrogen, depending on type of cloud, will be used to weaken precipitation,' meteorologist Zhang Qiang said. The bureau's chief engineer, Wang Yubin said these chemical seeding agents posed no threat to health or safety. 'Ground and water samples taken after experiments show the seeding agents are 'green' and do not have an impact on the environment,' he said. Up until a month ago, Beijing had been denying it would fire chemically loaded shells from cannons to force rain from approaching clouds before they gathered over the city. But a 50-50 chance of rainfall - and the same odds on a huge loss of face if the 'Bird's Nest' National Stadium comes in for a soaking - means little has been left to chance. After five years' preparation, which included scrutinising daily weather records over the past 30 years and deploying a fleet of hi-tech data-gathering planes, the bureau's deputy chief spokeswomen, Wang Jianjie, said the Olympic weather service and its manipulation capabilities had reached an 'age of maturity'. She predicted its performance would peak for the August 8 opening ceremony. Ms Wang and her colleagues will have some tough calls to make, as they are responsible for passing on the bad news if extreme weather is imminent. She said bureau staff would inform the Games organising committee, which would make the final decision on any rescheduling of events. She admitted Beijing's 'atmospheric conditions' played a major part in the capital's notorious air pollution. A major worry is the winds that carry pollution to the city from neighbouring provinces. Meteorological station chief Guo Hu told the South China Morning Post last night: 'The Beijing Meteorological Bureau has been consulting with international sports federations about the effects of Beijing's weather on athletes.' He refused to go into more detail.