Are you looking for a single mitigating factor as to why the Russians won/Germans lost? If so, there is no such answer. Amateurs will certainly point to the severe winter of 41/42 as the reason the Russians were able to stop Barbarossa. Others will point to the rainy autumn. Neither are correct.

However, the Russians were never going to lose regardless the weather conditions - that is, if you remove the rains and normalise the winter of 41/42, it wouldn't have made much of a difference to the overall direction of Barbarossa/Typhoon, or the campaign as a whole.

Generally speaking:

• The climate of European Russia hindered the operations of all the participating combatants.

• The terrain of European Russia hindered the operations of all the participating combatants.

• The infrastructure of European Russia hindered the operations of all the participating combatants.

The Russians were definitely much more cognisant of the above factors, which is evident in some of their design decisions, their mobilisation efforts, and their approach to conducting the war.

On the other hand, the Germans were just really dumb. They categorically ignored the above and a number of other salient points that doomed their proposed conquest of European Russia from the start.

The above three bullet points were ignored or determined to be non-issues by German planners prior to launching Barbarossa. In cases where research or war games said otherwise, there was considerable pressure (both from high command and as a product of hubris) to diminish the potential effects.

In addition to the above issues not being considered as impediments to German success, the Germans also failed to prepare their military for even a short campaign in Russia. Very little was done to provide its forces with the superiority of arms required, the necessary reserves, or adequate logistical support needed to conduct the largest military operation in modern (if not all of) history. This is of course ignoring the additional burden placed on the armed forces of having to conduct a genocidal campaign behind the front (which only exacerbated the problems the combat forces would face).

In addition, the state (in terms of make up, ability, mobilisation potential) of the Soviet forces, the capabilities of its command staff, and the massive industrial potential that the Russian state possessed, were considered almost superfluous to German war planning.

Unfortunately for the Germans, everything they ignored up until June 22nd, 1941, came to the forefront within a matter of weeks of launching their attack. While on the surface, and definitely within the confines of OKH, the campaign's early days were seen as an unqualified success, the reality of the situation was as follows:

• The German armed forces were ill equipped to fight in Russia.

• The German armed forces were too few in number.

• The German armed forces lacked adequate reserves in every category of men and materiel. There weren't enough men to support the losses incurred, there weren't enough spare parts to support the wear and tear on vehicles, etc.

• The German armed forces had too few modern tanks, too few modern planes, too few modern and robust trucks, too few modern weapons, too few hardy horses, too few locomotives, etc.

• The German armed forces - in totality - lacked the necessary logistics capabilities to conduct a conflict on this scale.

• The German armed forces were grossly ignorant of the state of the Russian road and rail network, and suffered terribly as a result.

• German industry flat out sucked. They couldn't hope to produce what was needed by its combat forces, and were forced to rely on captured materiel (which often proved problematic).

I haven't even touched on how badly the Soviet Armed forces were underestimated by the Germans. If you take just the points I noted above, I'm hoping it's pretty clear that the weather was really just another "straw on the camel's back" and not what decided the fate of the German foray into Russia. The Germans had set themselves up to fail before firing a single shot.