Necessary, but not sufficient condition though.
Sweden tried in the winter, and failed for example.
You thought of this in the shower? I feel dumb.
Pro-tip: invade from Mongolia.
Both Napoleon’s and Hitler’s armies were destroyed even worse by winter once it came.
How’d that work out for Napoleon and Hitler, just to name a couple.
Found: https://www.wikipedia.org/wiki/Invasion_of_Russia
But can’t be arsed working out which started in winter vs which where destroyed by winter.
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.
There are, of course, more problems.
