How does a hood scoop work?

I ran an open dual snorkel scoop on the street for about three years on a daily driver (I also had fenderwell headers). This was in Kansas, rain, snow, whatever, the car was my only transportation besides a motorcycle. The engine wasn't sealed to the bottom of the hood, I just had a 14" open paper-element air cleaner under the scoop. I only plugged the the hole in the hood once. It was the middle of January & my Mom & I were making a highway trip of about 210 miles each way. Too much cold air was coming through the firewall somewhere & the heater couldn't keep up. I stopped at a rest area & shoved a piece of cardboard into the scoop to keep some of the cold air from coming through. Other than that one time, I never closed off the scoop & I never had a problem.