Scent will rise up, cool, loop back down, heat up again, rise back up, etc. The dog will alert, put it's headup, then lose the scent. An experienced handler will mark the map and possibly can get a direction from a line of these alerts. Sometimes several dogs in the field will establish the line over half a mile or so in this way, pointing to the subject. Wind carries scent to the dog, but also disperses it.
Convection disperses it too, even more so.
Only 100 ft. Areas searched morning and evening are much higher than midday in summer. Dogs navigate most brush better than most people. Dogs tire in deep powder snow, but the heavier coated breeds will still search. The handler will bring some, but on an extended search you should get a 50lb bag of the handler's brand for your teams.