Combined is the headline number: the ballpark’s own effect combined with today’s weather, measured against the MLB average (so +10% means about 10% more home runs than a neutral environment). Weather isolates just the day’s wind and temperature, scaled by how wind-receptive the park is (high at open yards like Wrigley, low where the walls block it). Park is the venue’s own 3-year Statcast effect. Dome and retractable-roof parks show no weather, so Combined equals Park. Park factors are a secondary effect (a 450-foot bomb leaves any yard), so don’t lean on them too hard for a single game.
