High winds are detrimental because they blow the scent away and dilute it before the dog can sample it. Light winds help because they spread the scent cone over a larger area for the dog to detect, and the dog does not need to search in a tight pattern. If the ground is warmer than the air, the track or article scent will rise and be available. If the ground is colder than the air, the scent will not rise and will not be dispersed, so the dog may have to put his nose right on the article to find it. This makes for a particularly impressive public demo, but the dog will not do as well on a week old crime scene where the articles are the same temperature as the ground.
Rain seems to have a detrimental effect on scent availability when searching for evidence.
Returning to the same area five minutes after the rain stopped, the dog easily found all the articles. Apparently scent is driven downwards during a rain and is less available to the dog. Scent will also be less available when the ground is colder than the air and the sun is not heating up the ground. This means that early mornings and cold, cloudy days are not the best times to search older crime scenes. Dogs can detect objects which are under water.