No pony could remember a time when it had rained so hard.
This storm is the perfect cover.
Rain poured down the back of the purple unicorn as she slinked around the rear of the magic shop. She peered in through a single foggy window. The inside of the shop was cloaked by shadow.
She must have closed down because of the storm. Excellent.
The unicorn's horn glowed with magic and the window slid up slowly. She glanced around cautiously and then proceeded to lift herself carefully though the window.
The room smelled of dusty arcane tomes. Above, the rain on the roof sounded like the drumming of hoofbeats.