Air Density and Pattern Density
Air exerts a drag on pellets just like bullets. Higher air densities mean more drag. Pellets will disperse more as this drag increases. So as air density increases, pattern density decreases, and so does your max range.
It is important to understand what causes high air density as this will reduce the effective range of your patterns. Low temperature causes higher air densities and that one factor will probably influence your range more than anything else. Your max yardage can change by a few of yards during a turkey season due to temperature changes.
Barometric pressure, humidity, and altitude also affect air density. High barometric pressure means higher air density. Low humidity means a higher air density. Low altitude means a higher air density. In the big scheme of things, these 3 factors can be considered negligible for turkey patterns. However, if you would prefer to record the air density against your pattern rather than just temperature, there are wind meters that will provide this information (search this site). There are also air density calculators on the internet if you know the individual component values (temp, pressure, humidity, and altitude).
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