Many of the Heer's general officers had experience with the climatic conditions of Russia during the First World War and many of them were aware of these difficulties. However, both the OKW and OKH planners for Barbarossa planned to defeat the bulk of Soviet armies before the onset of winter. In January 1941, Luftwaffe quartermaster-general, Lieutenant-General von Seidel met with OKH head Halder in a conference coordinating the supply situation between the Heer and Luftwaffe, von Siedel broached the topic of winter clothing, his Heer counterparts tersely noted that the campaign would be finished by winter. For the most part, the German military establishment took a cavalier approach to the capabilities of their Soviet enemy and their thinking mirrored that of Hitler- that one swift kick would lead to a collapse of the Soviet state. The campaign planners anticipated that the winter would mostly be a mopping up operation whose troops would require a minimum of supplies.

This massive underestimation of Soviet capabilities led to a disaster in late 1941 as the logisitical system of the Wehrmacht began falling apart at the seams. Not only had the Red Army continued to fight despite massive losses in the various cauldron battles, but Barbarossa's logistical network was incapable of adequately supplying the German armies in the field. Instead of mopping up, German troops were engaged in offensive operations in November 1941 that ate up equipment and ammunition at a prodigious rate. In such a overburdened logistical system, winter clothing often had a lower priority than fuel or ammunition.

In short, the "titans" of the German General Staff were in a dire situation of their own making. Their planning for Barbarossa was careless and they brushed aside inconvenient details that suggested defeat of the USSR would take more than a single campaign. Victory over France in 1940, which few officers in the Heer had actually expected, had engendered a fatal overconfidence which dovetailed with other problematic components of the German way of war.

But in one small way, the German planners of Barbarossa managed to wring a victory of sorts postwar by foisting all the blame for the campaign's missteps upon Hitler. The already common trope in the West of of "Russia's General Winter" (which itself is not true- Napoleon's Grande Armee was a defeated force by the winter of 1812) lent this distorted and selective memory of 1941 a degree of legitimacy.

This was covered in earlier posts so feel free to do a search. The short answer is that the Germans expected the campaign to be over before the winter. They invaded the USSR in June, which left them at least 4 months to campaign before the cold weather would set in. Their invasion plan, Operation Barbarossa, anticipated the Germans would capture Moscow and destroy the bulk of the Red Army in the fall of 1941. The Nazi leadership had a low option of the Soviet military capabilities and political structure, and expected the country to simply collapse at that point.

They did expect them. Thats why Barbarossa began in June. They just expected to have taken Moscow by winter. They didnt expect the fierce Russian resistance, and Hitler's decision to turn troops away from Moscow and south towards Stalingrad. They planned to knock Russia out by the first snow, but due to bad planning, they were bogged down, far from their target, fighting in Stalingrad and the vast expanse of rural Russia when winter struck.