Storming Skies

Storming Skies is the 1st book of the series.

Spoilers
Rainstorm is seen with Darkpaw and Windpaw saying how 4 ancient clans were born.

BrightClan,

RainClan,

BreezeClan,

NightClan.

(Note: all clans except RainClan vanished after this book.)