Some of the things that will affect the trajectory of a bullet:
Muzzle Velocity - time of flight
Ballistic Coefficient - drag, time of flight
Altitude - air density, powder burn rate
Humidity - air density, powder burn rate
Temperature - air density, powder burn rate
Barometric pressure - air density, powder burn rate
There are counter-intuitive things that happen as well. Higher altitude means thinner air, but dry air is thicker, so if you are at a high elevation but the air is extremely dry the two variables work against each other. Also, colder air is more dense than warmer air, and often with the altitude increase the temperature drops. Yes, humid air, air with more water vapor, is thinner.
Temperature affects the barrel as well.
I recommend getting a feel for how your gun and cartridge behave in the conditions you are hunting. A log book of the results is important to refresh your memory, but you can hardly go hunting one year and the next year find the same weather conditions the next year. That is why I feel that if you are serious about filling your hunting tag you use a cartridge that appears to be less affected by conditions, thus shooting a 300 Win Mag over a 243, stuff like that. Just my opinion. The more variation in conditions the more you need a fast, heavy bullet, with a high ballistic coefficient.
And we haven't even talked about wind drift, and something that few consider is that wind doesn't flow horizontal to the ground, there are down drafts, up drafts, and all the variations in between. Imagine shooting across a ravine, the shot may be 300 yards or so, but the air moving in that ravine can be going everywhere. Another argument for a fast heavy low bc projectile. The less time you are in the air, and the more mass you have, the less you will be pushed and pulled and slowed due to drag.
http://www.theweatherprediction.com/habyhints/260/
http://www.riflebarrels.com/articles/bullets_ballastics/ballistic_altitude_temperature_humidity.htm
http://www.accurateshooter.com/technical-articles/ballitics-altitude-and-air-pressure/
http://longrangeshooter.com/2009/02/temperature-effects-on-zero/
https://www.ballisticproducts.com/b.../curmudgeon_articles/060329_hotcoldpowder.htm