Book excerpt: Search the web and you'll find various analyses of the impact of weather on NFL games. They all have one thing in common-the analysis is good, but the underlying data is suspect. Until now, most pro football weather data are based on daily high, lows, or averages for temperature, wind, and humidity; based on city climate averages; taken from dubious league gamebooks; missing cloud cover and precipitation; based on kickoff conditions only; based on recent or narrow timeframe; unsourced (i.e., where did the data come from and when was it measured?). In this second volume of his Pro Football Almanac series, Mark Wald collects empirical weather data for every outdoor pro football game played since hourly surface observations became standard-the 1940s for most teams, back to 1937 for a few others. 12,189 games covering three professional leagues: AAFC, AFL, NFL Temperature, humidity, wind, gust, wind chill, cloud cover, and precipitation Up to four data points per game, covering three hours Measured at the time games were played, by the nearest NOAA weather station Pro Football Almanac Vol II is the most accurate pro football weather resource ever compiled.