Water leaking in. Where is it coming in from?

This problem just started happening a couple weeks ago, but every time it rains I get water leaking in and it just pours out from under the dash behind the glove box. If my car sits outside while it's raining and I take it out for a drive it comes pouring out and I'm not talking about just a little bit of water, I mean like a gallon pouring out onto my passenger floor board. How is it getting in and where is it being stored because it only comes out if I turn a corner or punch the gas.

Anyone else have this problem? This is getting very annoying having to soak up all the water every time it rains. I can't tell where the hell it's coming in from.

Thanks guys. I think I got it fixed. I stuck my finger up the drain on the passenger side and about two gallons of water poured out. The other side wasn't clogged. Now I want to take the plastic vent off and clean it out real good but I couldn't figure out how to get the windshield wipers off. I got the nuts off but they wouldn't come off of the bolts. Any tips?