99 Lumina Defrost Problem

The other day I was driving and it started raining like crazy. Once the rain stopped my outside windshield started fogging up around the area of the wipers. I had to keep the wipers on to stop it from fogging up in that area even though it wasnt raining. Can someone tell me the cause of that?

my 90 does the same thing when the a/c is on turn up the temp on the fancontrol