The temp variation is very minimal up to 500 yards or so. At 1000 yards the temp difference will be greater, but the bullet's initial BC is important. Further out its proportionally different between the initial BC of the bullets. The differences below equate to a 10 degree change in temp. I hope to think we are able to guess within a 10 degree change in temp. NOTE the BC change is twice that for the hi BC bullet.
3000fps .400 BC drop = 321.37" drop, 102.432" drift at 1000 for 200 yard zero
3000fps .405 BC drop = 318.01" drop, 100.848" drift at 1000 for 200 yard zero
3.3" drop and 1.4" drift at a 1000 yards
3000fps .800 BC drop = 213.38" drop, 43.648" drift at 1000 for 200 yard zero
3000fps .810 BC drop = 212.35" drop, 42.944" drift at 1000 for 200 yard zero
1" drop and .7 drift at 1000 yards
As mentioned, humidity seems to make ZERO difference at any rifle distance.
Barometric pressure changes are exactly like temp changes. A half a BAR change is pretty much exactly like the example above. Going from 29.53 to 29 changes the BC's to .407 and .815. Personally, unless my knees ache, I have no idea what the pressure is but the forecast is normally accurate enough for this.
Think of it this way, are you a gadget guy and will you be shooting game at 1000 yards or more? Fairly sure you will be using a hi BC bullet though.