Moscow and Saint Petersburg have a humid continental climate. Saint Petersburg has a lot of influence from the Baltic see tha bring warm, wet and short summer and long cold winters. July and August temperatures can get up to +30C. The coldest month is February, temperatures may drop till -30C.
Baikal lake region (Irkutsk, Ulan-Ude) have temperatures between -20C and -40C during the whole January and February. Lake Baikal freezes at late December or January and keeps frozen till May. The best filming period is MArch as the temperatures are mild (between -5C and -15C and sunny).