The aerosynoptic conditions in the Moscow region on May 9, 2021 was determined by the rear part of the cyclone centered in the White Sea area and the passage of the axis of the high-altitude hollow. At night and in the morning, the Moscow region was crossed from southwest to northeast by a multi-layered cloud system consisting of layered rain clouds with a lower boundary of 200-300 m and cells of recessed convection with height of 5-7 km.

The width of the precipitation zone, which shifted to Moscow at a speed of 20-25 km/h, was 150-220 km. With a background intensity of precipitation about 1-2 mm/h, the intensity of convective precipitation in some places was 10-15 mm/h.

In accordance with the flight plan, at 0:00 MSK, Yak–42D “Roshydromet” meteorological laboratory (b/n 42440) was lifted into the air from the Chkalovsky airfield and sent to the Naro-Fominsk — Obninsk area at distances of 120-210 km in order to investigate the meteorological characteristics of the atmosphere and clouds. Due to the fact that the zone producing precipitation with an intensity up to 5-10 mm/h was moving towards Moscow. At 01:25 MSK works on cloud seeding were started using liquid nitrogen (Fig. 1). The work was carried out in conditions of severe icing until 01:45 MSK, when the aircraft was forced to stop the seeding activity.

Taking into account the complicated meteorological situation in the period from 02:01 to 03:30 MSK, six more AN-26 aircrafts were launched and were sent to the area bounded by azimuths 2830— 2050 and ranges 50 – 160 km from Moscow to carry out effects on clouds flowing into the city from the southwest and west.

At the same time, at distances from 120 to 160 km, AN-26 aircrafts carried out cloud seeding with granular carbon dioxide and liquid nitrogen, and aircrafts operating at distances from 50 to 80 km used packages with coarse powder as a reagent. The purpose of the conducted impacts was to prevent the advance of the impending precipitation zone in the direction of the city, as well as the dynamic suppression of the clouds flowing into the city.

In the period from 05:35 to 06:05 MSK, three more AN-12 aircrafts were lifted into the air to help the AN-26 aircrafts, which were sent to work at distances from 25 to 70 km with azimuths of 1900 — 3100, where they performed intensive cloud seeding using packages with coarse powder.

After the impacts, all the aircrafts that used up the reagent were sent to the Chkalovsky airfield for refueling and loading with the necessary amount of reagents, after which repeated flight were carried out. Due to the seeding, precipitation was avoided on the territory of the city until 10:55 MSK (Fig. 2). According to meteostation data, drizzling precipitation was observed on Red Square from 10:55 to 11:15. Episodic drizzling precipitation was observed in some areas of the city until 12:10 MSK.

Due to the fact that there was a precipitation zone to the west of Moscow area, at 12:29 MSK an AN-12 (b/n 10) aircraft took off again, which continued exposure with packages of coarse powder in the immediate vicinity of the Moscow Ring Road, which made it possible to exclude precipitation in the territory of the city.

In agreement with the Customer, the work on the impact was stopped at 14:00 MSK.

A total of 17 flights were carried out on May 9, 2021.

Fig. 1. Digital maps of the height of clouds and precipitation intensity at 01:30 MSK on May 09, 2021.

Fig. 2. Digital maps of the height of clouds and precipitation intensity at 10:50 MSK on May 09, 2021.