According to Wikipedia, the Russian Airforce used weather modification to ensure clear skies and balmy weather for the G8 Summit held this past July 15-18 in St. Petersburg.
“…three Russian Airforce M-17/M-55 high-altitude reconnaissance planes flew several sorties and dispersed 2400 liters of liquefied nitrogen, 20 tons of granulated CO2 snow, 500 silver-iodide pyrotechnic canisters and 100 bags of moisture condensation reagent bags into the stratosphere. This operation was intended to evacuate the airspace of excess humidity over the Finnish Bay and St. Petersburg itself, by artificially inducing overnight rainfall. The cost of the flights and equipment totalled 20 million rubles (approx. US$750,000)”