Can anybody from Russia or someone who has traveled to Russia in mid September tell me about the weather in Moscow and St. Petersburg?
My travel dates are 11 September to 17 September. Does it usually rain during this period every year? I’m scared of my trip getting ruined 
No, it usually does not rain.
My memory of the weather in Moscow was of very dry, baking hot summers (which can last well into September) and then months of freezing snow and ice (starting in late October or in November). Grey, rainy, autumnal weather wasn’t much of a thing.
The only rain I particularly remember occurred during massive thunderstorms, which were not that frequent but when they did occur they were accompanied by huge downpours. These typically occured at the height of summer, not in September.
Turns out my memory corresponds with the facts: if you google the weather in Russia it says the country doesn’t get a lot of rain and most of the precipitation occurs during summer thunderstorms or in the form of snow in winter. July is the wettest month.
@Jabod Thanks for the detailed response, that sounds pretty reassuring! ChatGPT and Gemini told me bad things about September rains so my heart sank!
Possibly the warnings of rain have more to do with St Petersburg than Moscow, as St Petersburg has a somewhat wetter climate because it is near the sea. Of course, it might rain occasionally in either city, as in any European city, but I think you would have to be unlucky to experience constant downpours every day.
@Jabod Gotcha, gotta be ready with umbrellas!
My trip is over, there were no rains, instead super nice sunny weather every single day 
I agree with you. I was just in Pete / Pskov area for about 3 weeks. Got lucky that it didn’t rain too much. We had a really clear sunny day and we took advantage of the canal cruise in Saint Petersburg. Great weather for this time of year. I think we got in and out before it starts getting bad.