It's in the heart of Mission Valley, 5 to 7 miles north of downtown San Diego. Valleys seem to hold the heat more. It is also within 5 miles of the coast. On gameday, being closer to the ocean proved to be more humid. I live about the same distance from the ocean as Qualcom stadium but north of the stadium. It was definitely a crazy hot and humid day that we don't usually get. A hurricane weather system had been pushed from Mexico into our weather system. Again, doesn't usually happen.
Weather, IMHO definitely played a factor, but both teams had to play in it. San Diego maybe had the advantage from getting more used to the heat and humidity. I don't think Marshawn played much in that game because he couldn't deal with the heat, again just my opinion.