peyton played for a dome team for like 12 years so every shitty weather game was an away game
confounding variable
Yoooooo, I see yoooouuuu. Bringing out the confounding variable to disprove my correlation is causation assertion. Niccceee!
Except the problem is that in calling Peyton's being away in those games the confounding variable you've effectively asserted that the real reason Peyton performs poorly in cold/shitty weather isn't anything else EXCEPT the fact that he's on the road. Which would therefore imply that Peyton Manning sucks in the vast majority of his road games and not just the cold ones or the ones with shitty weather.
And because you did that I get to do this:
Peyton Manning Career Home Stats:
65.9% Completion (2725 Completions/4134 Attempts) 7.81 Yards per Attempt (32288 Total Yards) 253 TDs 96 Ints
Win-Loss: 90-29
Peyton Manning Career Away Stats:
64.9% Completion (2723 Completions/4194 Attempts) 7.56 Yards per Attempt (31721 Total Yards) 228 TDs 122 Ints
Win-Loss: 75-43
So what do we see? We see that Peyton is clearly losing more games on the road, so there is definitely a positive correlation (well done you!). However, it appears as if his performance is almost identical at home and on the road, which then completely and utterly sinks your theory that the confounding variable for Peyton's poor performance is simply by virtue of being on the road.
Peyton Manning performing poorly in the cold is also a myth (you can look up the numbers on that anywhere there've been like 40 articles on it in the past week).
However, not a single database I could find tracks the weather beyond temperature. So I can't easily look up the numbers necessary to show that Peyton is universally very terrible when the winds get flippant or when a storm is brewing and markedly less bad when the weather isn't so shit. So I still lose, but maybe one day when I'm just THAT fucking bored, I'll scour through every single game Manning's ever played to find the ones with weather and do a comparison.