Weather conditions on June 12 in Moscow region was defined by the passing of a cold front with waves. In Moscow and surroundings on June 12 at 4:00 am there was windless cloudy weather . Ground temperature prior to the rain was 15-16 ° C, relative humidity 83%. Above the surface inversion layer the atmospheric stratification was potentially unstable. The zero isotherm was located at an altitude of 3000 m and the tropopause — at 12 km .
By 4 o’clock in the morning in the west of Moscow Region in the area of the cold front there were multilayer stratus and rain clouds. The area of the steady downpour with with increased intensity in the cells of embedded convection was moving at the course of 60 ° in the direction of the city at a speed of 50 km/h. In the area of the works were observed storm centers with cloud top 10-12 km ( Fig. 1).
With consideration of the difficult weather situation 7 aircrafts took off from » Chkalov «-aerodrome from 4:00 to 5:45 (4 AN- 12-s and 3 AN- 26-s ) to carry out work on the effects of clouds . Intense exposure were performed at distances from 30 to 200 km from Moscow in the altitude range 4200-8000 m. As a result of the work the areas with the rainfall have been reduced and the rainfall intensity was reduced by three times ( Fig. 2). However it was impossible to exclude rainfall over the city completely between 5:00 to 10:40. During the work the aircrafts exhausted their supply have been replaced in due course. The impact has been performed until 11:45 and were completed due to the complete suppression of rainfall on the approach to Moscow.
Subsequently the aircrafts carried out monitoring of the atmosphere until 11pm when all the aerial works were stopped by instructions of the General customer.