Due to the forecast of the difficult weather situation the Moscow Authorities have decided to conduct works on meteoprotection of Moscow during the celebration of the City Day from 4am on 7 Sept until 0am on 8 Sept. Upon request of the Government of Moscow the Chief of the General Staff of the Defense Ministry instructed the Chief Command of the Russian Air Force to set up a group of 10 aircraft An- 12 and An -26 ( 9 primary and one backup) at the «Chkalov» aerodrome.
Synoptic situation over the center of the European part of Russia on September 7, 2013 was defined by extensive sedentary occluded cyclone with the round-level center in the region of Tula. Early in the morning the weather conditions in the Moscow region were defined by the cloud system of the occluded front slowly moving through the Moscow region from east to west. In the city and suburbs there was a multi-layer cumylus and layered rain clouds . In the troposphere north- easterly winds dominated up to the height of 11km . The atmosphere was stably stratified , it was steady downpouring.
After 11am the cloud system of the occluded front has moved to the west and the air began to warm-up causing rapid development of cumulus and cumulonimbus clouds in the layer 250-4500 m Ridges of convective clouds were forming in the immediate vicinity of the Ring Automobile Road to the north- west and south- east of the city .
After 3pm there were elongated ridges of cumulonimbus clouds despite the ground temperature stopped increasing.
According to the meteorological situation aerial work can be divided into three stages: Stage 1 4am-12pm , the 2nd Stage 12pm-4pm and the third stage 4pm-11pm.
Work commenced at 4am with raising 5 aircrafts ( four An- 12 and An -26) from aerodrome «Chkalov». At that time the rainfall intensity in the city was up to 2.3 mm / h and the top of the cloud reached a height of 5000 — 6000 m ( Fig. 1).
At the first stage in the air were 9 aircrafts. Aircraft produced effects on clouds at altitudes of 3900 to 4800 m in the eastern and south- eastern sectors at a distance of 50-100 km from the Moscow Ring Road. Intensive work on modification of clouds over the city resulted in stopping raining at 07:30 ( Fig. 2) (somewhere observed occasional weak drizzle only) , and from 11.10am the rainfall stopped completely and the clouds were partially scattered.
At the second stage in the air were 7 aircrafts producing effects on the intensively developing convective clouds at altitudes of 2,400 to 5,200 m in the same sectors up to 180 km away from Moscow. During this period, precipitation ( intensity 0.1-0.2 mm / h ) were observed in the east and north -east on the border of Moscow.
At the third stage, in the air were 6 aircrafts producing impact of individual convective clouds at altitudes of 2400 to 4900 m in the north , east and south- east up to 120 km away from Moscow ( Fig. 3). During this period precipitation in the city was not observed.
The works on the impact on September 7, 2013 have been completed at 10pm as agreed with the Customer.