With new and better data, I redid the study. This time I have actual temperatures and used all non-preseason games from 2000 through the wildcard round of the 2011 season (last Sunday). Here are the results. The graph below depicts the winning percentage of the road team by temperature at kickoff. Road teams are classified according to their home climate--dome, cold, moderate, or warm.
Just as we saw in the original study, dome teams playing in cold weather appear to be at a severe disadvantage. And just as we might expect, teams from warm cities struggle quite a bit as the temperature drops. The teams from moderate climates are less affected, and the teams from cold climates don't appear to be affected at all.
Sample sizes get smaller as the temperature drops. In the 11-20 degree bin, there are 17 cold visitors, 8 dome visitors, 9 moderate visitors, and 6 warm visitors. In the 21-30 bin there were 45, 15, 32, and 19 cold, dome, moderate, and warm visitors. Taken as a whole, however, the trends appear undeniable: The less acclimated a team is to a cold climate, the worse it fairs.
Zero out of 8 dome teams in the data set won in cold weather 20 degrees or below, and only 3 out of 23 (13%) have won in temperatures 30 degrees or below.
There are two potential dome at cold match-ups for the remainder of the playoffs--New Orleans at Green Bay and Houston at New England.
A few notes: 308 out of the approximately 3000 games since 2000 did not have temperature data recorded and were excluded. I haven't checked them all, but I suspect a good chunk of those were played in domes. Super Bowls were excluded. Climate classifications were based on city average wind chill for the month of December. Cold teams were BUF, CHI, CIN, CLE, DEN, GB, KC, NE, NYG, NYJ, PHI, and PIT. Dome teams were ATL, DET, IND, MIN, NO, and STL (and DAL after 2009 and ARI after 2005). Moderate teams were BAL, CAR, DAL, OAK, SF, SEA, TEN, and WAS. Warm teams were ARI, HOU, JAX, MIA, SD, TB.