Did the winter/conditions really make the Germans lose at Stalingrad

I hate the fact that my sources are usually post-facto but I have at least one this time. But here goes an attempt at answering it, well abridging it really.

The winter definitely did help, after all there is an increase in the attrition rates and wear and tear on soldiers in the winter. However there were massive problems with the extremely large offensive before the entire winter even arrived.

By the time the Axis arrived at Stalingrad most of the grain and food supplies were taken out of the city itself. This mean that by the time the Germans took the city months later, there was no food. This was further exacerbated when after the Germans took the majority of the city (over a long arduous 3 month time period where supply lines were already stretched and thinly protected (this will be important later)), the Germans were forced to keep the city.
The actual fighting within the city was done before the winter even hit. The Germans took high amounts of casualties (as did the Soviet forces) due to the close and building by building fighting. It didn't help that most of the fighting and engagements was strategically staged where the Soviet forces would be as close to the German lines to negate support fire. All in all, the Germans spent three months taking block by block a city they would have to defend all the while suffering large casualties in both their army and air force.
By the time November would roll around (i.e the beginning of winter) the total offensive directed towards Stalingrad would actually cost the Axis dearly as the thinly defended supply lines defended by less well equipped Romanian, Italian, Croatian and Hungarian forces were ripe for attack. It also didn't help that most of the bridges weren't secured and neither were the flanks. By the time the Russian counter offensive began (in November) the Axis had been stretched too thin and had concentrated too many resources in trying to keep the city.
Once the counter-offensive began, the winter weather only served to exacerbate the chaotic situation the Wehrmacht was in. The flanks were attacked, the supply lines were cut, most of the air force had been wiped out and the VVS had achieved numerical superiority. The situation would pretty much prove very dire for the Axis since Soviet flanking action cut off the Sixth Army (AKA the occupiers of Stalingrad). This would prompt Field Marshal Erich Von Manstien's attempt at creating an "air bridge," a way to supply the encircled Sixth Army via air support to buy time for the Sixth Army to break out of the encirclement. Of course the problem was the Sixth Army was huge, and it had the 4th Panzer division along with it. There was no physically feasible way that the Luftwaffe could have shipped enough supplies to allow a breakout of the encirclement. All of these decisions would cost the Germans dearly given that the transportation forces ended up losing over 1000 bomber personnel and almost two entire transport groups.

This is where we diverge, because the reasons formerly stated are reasons why Stalingrad would have been a failure for the Axis despite the winter. However here are things that DID affect the Axis because of winter.

Manstien's advance and the failure Operation Winter Storm. German tanks had suffered rather badly in the rough and wet terrain in the December attempt to break out Paulus' 6th Army. Because of the rough terrain and German Armor having weak all-terrain capabilities, the advance was slowed down considerably. Even though the advance was initially rapid due to Soviet forces not being aware, the Soviet response soon slowed down Manstien's 6th Panzer division.
The inability of a breakout: By December, Paulus and the 6th Army that was encircled at Stalingrad had less than 80 tanks operational and was snowed in. The lack of mobility and the disabling of a good amount of the encircled Axis vehicles would eliminate any attempt at breaking free of the Russian encirclement.

All in all, the Winter did play a part. It was a catalyst that worsened the already dire situation that the Axis was embroiled in. In terms of how it affected the Russians, The Russians were better prepared, but still suffered a massive attrition rate in Stalingrad. The most beneficial part was that the snowfall that would occur during the counteroffensives served to hinder the German advance due to their narrow tracked tanks, something the T-34 didn't suffer from as much.

However my knowledge is much more familiar with aircraft so I'll talk about that:

The winter massively hindered the air support that the Luftwaffe was able to commit. Due to snow, supply issues and generally bad visibility, the winter definitely did not help the Axis in terms of aircraft. And although the BF-109Fs and FW-190s that would be fielded in the battle of Stalingrad most of them didn't suffer too many issues outside of being snowed in and being in unfavorable circumstances due to most of the battle taking place in lower altitude. Well that and the problem of engines seizing due to oil and coolant freezes, but this applied to both sides.

The Soviets on the other hand suffered a large loss of aircraft before winter arrived, suffering from a general lack of high quality equipment (although this was relatively rectified in part to the much better performing Yakolev Yak-9) at the beginning phases. That said by the time December arrived the Luftwaffe air superiority had begun to diminish as did the bombing superiority given that supplying the 6th Army became a priority.

All in all, I'll still maintain that the winter while a contributor to the Axis defeat, only served to exacerbate an already strategic and tactical impossibility. The Axis situation at Stalingrad was untenable logistically, strategically and tactically. Even though they managed to hold Stalingrad for a short duration, the price the Axis would pay (as well as the Soviets I'll add) was astronomically high.

Murray, Williamson & Millet, Alan War To Be Won, Cambridge: Harvard University Press, 2000 page 288.