Local control of precipitation:

Scientists in Genève university are working in a new system to condensate water in the athmosphere.

Is not the first experiment, the most common approaches consisted of dispersing small particles of dry ice, silver iodide, or other salts in the atmosphere.

This new method, is based on photochemical formation of p.p.m.-range concentrations of hygroscopic HNO₃ in laser filaments, that will join H₂O particles and finally, if the particles are big enough, it will rain.

Source: www.nature.com