On September 11, a strong tropospheric passage ("duct") in the VHF bands occurred in the St. Petersburg area. The passage of VHF is associated with weather favorable for the propagation of radio waves and tropospheric inversion.

On September 11, 2021, after cold and windy days, cloudy but warm weather and no wind set in. Daytime air temperature +17...19C, no precipitation. During the day at the dacha, I observed a sharp improvement in the refraction of radio waves (the R7 repeater could be heard 50 kilometers away with a rubber band antenna from the ground). I arrived in the city in the evening. On the way home in the car, I automatically searched for 93.6 on the FM band - I don’t know where or what radio station was broadcasting the news at the beginning of the hour.

At home I turned on the VHF transceiver, 144 MHz band. In the WSJT-X program, I managed to make several long-distance and interesting QSOs in the range of 2 meters using the FT-8 digital mode using an uda-yagi antenna with 3 elements in the “horizon” and a power of 50 W.

RA1AEP de RA1AHQ
distance ODX=156 km

RK1AA de RA1AHQ
distance ODX = 111 km.

RC3D de RA1AHQ
distance ODX = 503 km

Many stations are visible on the “waterfall”; it is also obvious by ear that many radio amateurs are working on the air:

Aerological diagram
The air is moist near the ground, dry above it, and moist again at high altitudes.
There is no significant increase in temperature with altitude. There is a sharp gradient of air humidity in the atmosphere.
Perhaps the “passage” was accompanied by the temporary formation of a tropospheric channel (waveguide) between the layers of air.
Air temperature in the evening +13C, humidity 89%, pressure 760 mm. mercury column (1013 hPa).

P.S. At 21:00UTC Pulkovo airport reported the weather:

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