Between Derpy's less the stellar lead and your own inexperience when it comes to working with clouds, the two of you only manage to cluster a legful of dripping grey clouds. And to make matters worse, it took you too long.
As the two of you push your charges toward the fire, its already managed to reach the outskirts of town. Ponies are once again panicking in the streets, with the injured limping desperately away from the creeping fire and the few able bodies trying to help.
"Ok, lets do this!" You shout to Derpy, who cheers back to you in comformation.
The two of you angle over one of the buildings starting to catch fire and together squeeze your respective clouds for all their worth…..which is pitifully not enough. A small shower rains down on the burning tinder, sending up a screech of steam, but ultimately only making the fire work just a bit harder before you and your friend are out of ammo.
"Crud!" You shout, feeling the heat pushing up thermals at you and Derpy.
"Hey, do you hear something?"
"Derpy, we still have the fire to deal with! Pay attention!"
"I am! But I hear something weird. Like thunder. Maybe it will rain on its own?"
"I…don't think that's what's happening."
You can hear the thundering now that Derpy pointed it to you. Coming directly from the heart of the forest fire, still burning trees are being shoved aside, making way for something very, very big. And like the fire, it's heading straight towards Ponyville