How is rain leaking through the 1st floor ceiling of a 2-story house?

We just had a huge rainstorm, and during the storm, water started dripping down from our light fixture on the 1st floor ceiling in our kitchen. The ceiling around the light fixture is dry though, and there's no leaks or signs of water anywhhere on the 2nd floor! I don't know if its a leak from a 2nd floor bathroom, but its a huge coincidence that the water started dripping down during this huge rainstrom. Any ideas as to what's going on? I can give more info if needed.