Why does my toilet act crazy when it rains outside?

General Questions
#1

I just did a search for “toilet” and although there’s always a chance I missed it, saw nothing related to my question. BTW, there’s quite a few toilet questions in GQ.

Whenever it rains or storms (as it did last night in our fair city of Chicago), the water in my toilet bowl goes crazy. First, most of the water drains out of the bowl, leaving only just enough water to cover the hole. The remaining water shakes and sloshes around like someone’s shaking the bowl. The toilet flushes normally, but the bowl doesn’t fill up significantly again (to a normal level) until it stops raining. Nothing’s happened to clog the bowl (I swear), and I’ve noticed this only during stormy weather. So what’s going on in my toilet? Is it something to do with sewers and storm drains or whatnot? If it helps, I live on the fourth floor of an apartment building.

#2

There’s a venting pipe that lets air in drainage pipe when you flush. In a house it’s one of the pipes you see sticking out of the roof sometimes. I don’t know how they do it in an apartment. It could be that the wind from the storm is changing the pressure in the venting pipe which sucks the water out of the bowl.

Or maybe your toilet is scared of thunder like my dog Becky was.