Winter is perhaps the only time you can successfully invade Russia. Hitler and Napoleon invaded in the summer and failed. The Mongols invaded in the winter and won.
Necessary, but not sufficient condition though.
Sweden tried in the winter, and failed for example.
So an army can operate in the winter, but you've got to be prepared. At -40 degrees, your troops' hands will stick to their weapons; vehicles start to need extra equipment to start; horses need a pile of extra stuff to stay alive; and so forth. If you have all that stuff, the training to operate in the winter environment, and the fuel to stay warm, I think winter can be an excellent time for prosecuting warfare in Russia.
Meanwhile, the real problem with operations in the area is the spring and fall mud seasons, which absolutely destroy roadways and keep your armor from getting anywhere.