The weather has been extremely variable in the Clans in the past few years, with unusually aggressive summers and violent storms. This summer, it has been quite hot and intensely dry. As the weeks pass, it is clear that there will not be rain any time soon. Prey are beginning to die or leave the area. The Clans have no choice but to begin stealing food from each other, and conflict ensues. [credit to globally for plot idea + famine info]
JULY 17: Record heat begins to take its toll on the area. Animals start leaving or spending more time in their burrows, and hunting becomes more difficult.
JULY 23: More and more prey animals have left the area, and those who stay rarely leave their dens. The river grows smaller as it dries up, and frogs begin to die in the warm water. There is no rain.
JULY 30: The famine is in full force. It becomes nigh impossible to hunt, and some cats succumb to starvation. Others turn to twolegs to acquire food. The air feels bone-dry. On August 10, ShadowClan will begin stealing food from other clans to survive.
AUGUST 25: The heat begins to decline. Prey animals start to return, but it is still quite difficult to hunt. ShadowClan may still seek prey from other clans.
AUGUST 30: A storm moves into the area, bringing rain along with it. The river, thinned out by the heat, is slowly replenished. The food supply stabilizes, and the Clans celebrate with feasts.
(As for Thunderclan, Foreststar would not permit stealing prey from other clans, but she will be returning from a miniature journey with Lightningpaw and teaching as many warriors as possible ways to hunt outside their usual ways and borders to sustain the clan. As a former loner, she will leave accepting food from Twolegs up to the individual's decision, but kits will not be permitted it unless things get drastic, and she would warn any who choose to accept food from Twolegs to stay near the edges of the city so as to avoid Bloodclan. There will probably be conflicts with Riverclan over Sunningrocks again.)