There are a number of wild pets which are seasonal, weather or time-dependant, so if you’re looking to add them all to your collection, this should help.
These are all the ones listed under the Pet Journal which specify the conditions needed to spawn.
The Storm Peaks – snowing
Jaguero Isle, The Cape of Stranglethorn – raining
The Scarab Wall and The Scarab Dais, Silithus – Summer (21 June)
Cellar, Deadwind Pass – Midnight
Khadgar’s Tower, Talador – best chance after a server restart
Desolace – night
Tanaris – sandstorm
Winterspring – Winter
Turtle Beach, Krasarang Wilds – Sun – 9pm-midnight
Duskwood – night