“Проливной” (prolivnoy) rain, or “ливень” (leeven), is a downpour: the kind of weather that makes you want to stay at home. Another way of calling it is “льет как из ведра” (lyet kak iz vedra) - literally “pouring like from a bucket”, or “дождь стеной” (dojd stenoi, rain that’s like a wall). This kind of rain is considered "classic" for St. Petersburg weather.
A step up in the sense of a natural disaster is a “грозовой” (grozovoy) rain, or simply “гроза” (groza): a real storm with lots of lightning and thunder, but not necessarily with rain. According to the popular superstition, early spring storms spell a cold summer, - so we might still have the chance to enjoy some sunshine!
Still, it is not the storms that can really get to you in St. Petersburg: perpetual “моросящий” (morosyashiy, drizzling) rains are what usually makes everyone want to leave the city for the summer. In this case, the rain can go on for days without stopping (in case of a “затяжной” (zatyajnoy), a lingering rain), or cease for only a short time to start again in a couple of hours (which makes it a “переменный” (peremenniy), variable rain).
Finally, there’s a type of rain that most people love: the “грибной” (gribnoy, “mushroom”) rain, which is rain during sunshine. Such rains are usually really mild, and the common belief is that after them, it is the best time to go mushroom hunting.
Well, that mostly covers the most common types of rain. Next time, our topic will be “scientific” words that made their way into common speech!