It'll be wet/cool/cold in the west, then once you get past the Volga it'll be chilly, wet and cold. Wait, that all sounds the same, okay, it gets colder once you hit and get past the Volga, it's a problem bringing lots of gear, but still you'll need a heavy winter jacket and jumpers. Also longjohns are a must (never put the word longjohns on the net or on paper before).
An interesting alternative is to take the train to Uzbekistan or Krgyzstan, going to Bukhara via Ulyanovsk is very much fun, but you need to be in a 4space cabin to survive!
