I've been pondering this question of late as this time of year often brings unstable weather. I've often noticed that a bad days punting sometimes coincides with unusual weather. I'd like to hear from some people in the industry how the following affects some horses differently to others:
Really hot weather
Gusty winds
Slippery surface on a "good" track
Stormy weather with thunder and lightning (vvf!)

I bet all over Oz and only on good or dead but its hard to know if conditions are comfortable for the horses when you're a couple of thousand kms away. Maybe I'll have to get on the weather website before deciding to bet on a certain track.