Although a dog is able to smell things we can not imagine, there are several circumstances that might influence him or even prevent him from smelling at all.
Rain on the track can be both, good or bad. It depends on the amount. Moisture itself is a good help for the dog, because it opens up the scent and makes it easier for the dog to follow the track. But to much of it washes the scent away and the track is gone. What the critical amount of rain is, depends not only on the dog’s abilities but also on the surface of the ground.
If it is very cold, it could become a serious problem for the dog. The dog works with his nose very close above the frozen ground or snow and draws the air into his nose. Because of the cold air the nasal mucosa can adhere. The dog indicates that by agitating his head.
Dogs have a lot of problems to cope with heat. To cool down they hackle and sweat on their paws. Not only that they loose a lot of water while hackling, they also breath through their mouth. But as explained above, they have to stop breathing and draw the air into their nose if they work a track. Moreover the tip of their nose becomes dry but the need the moisture of their nose to open up the scent. At least the lack of water when working in great heat can lead to a total collapse.
Although moisture opens up the scent, dew is a heavy problem for the dog. By drawing the air dew-drops plug up the dogs nose and the dog has to agitate his head. A meadow can become an impregnable obstacle.
Apparently it must be easy for a dog to follow a track in the snow. Everyone can see the foot-prints and the blood easily. But what we can see is not what the dog can smell. If the dog is able to work on snow or not depends on the kind of snow and the general weather conditions. I don’t want to describe all kinds of snow at this time, but I want to give an example. Temperatures are going down the ground is warmer then the air/ falling snow. The snowflake comes to the ground and because of the difference in temperature the snowflake condenses. The flake becomes bigger and changes its structure and now looks a bit like hedgehog instead of a snow-crystal. While transforming the structure the snowflake encloses the blood, which is now no longer accessible for the dogs nose. Snow can be a serious problem but it does not have to be one. So don’t blame your tracker, if the dog refuses to work although you can see the blood. Besides the influence by weather, there are many other circumstances that influence the work on a track.
For example every change of the surface like woods to meadow, meadow to street etc. are difficult and the dog may need some time to find back to the track.
Tracking in a corn- or canolafield after rain is no easy going for the dog. The moisture stays between the plants and creates a microclimate of extreme high humidity which causes some problems for the dogs nose.
A tracking dog knows what he is tracking. But nevertheless he still is a hunting dog and very interested in all the sweet smells of all the other animals whose tracks he crosses when he follows the wounded one. That’s why wallows or rutting grounds are good places to cause some trouble. These are obstacles the tracker has to realize and help his dog through such tough places.
Besides the fact, that someone, who walks over the track spreads the scent and probably hair, meet and blood around, people in front and around the dog disturb the dogs concentration. First and foremost tracking is an enormous effort of concentration. If the hunter stays behind the tracker it is ok. All other people should stay in a larger distance. Always consider that if the dog recognizes he is wrong, he might come back circling and searching for the right direction. So stay away from the dog in a distance that makes it possible to work highly concentrated.