The pegasus' job in civilized Equestria is to use its weather manipulation talents to create all manners of meteorological phenomena in order to make sure everything is stable. Ponyville is small, but sometimes still requires larger storms to keep it in balance with the rest of Equestria. Huge storms with heavy grey thunderclouds, towering anvils of cloud, swirling with heavy rains and crackling with pure, almost completely wild and untamed bolts of lightning.

And those are the kind of storms Rainbow Dash loves best.