Your windows are fogging because the raindrops evaporate as they plummet through the air, saturating it with water vapor so the humidity level is very high. Plus, as you move forward your windshield is cooled by the convection of outside air over its surface. So if you blow that humid air over the inside of the windshield, and the windshield is cooler, it is going to cause condensation -- fogging.
A/C will dry the air out so that you get evaporation on your windshield instead of condensation. This is why hitting the "defrost" button on your climate control panel will automatically engage the A/C in non-ECON mode.
I'm seeing this problem a lot more in OR (wet, humid, cool days) than I did in MA (very cold but also very dry days). You can see its opposite if you run your A/C too cool down in the South of the U.S. during hot and humid summer days, where your cold interior causes condensation on the exterior of the windshield.
A/C will dry the air out so that you get evaporation on your windshield instead of condensation. This is why hitting the "defrost" button on your climate control panel will automatically engage the A/C in non-ECON mode.
I'm seeing this problem a lot more in OR (wet, humid, cool days) than I did in MA (very cold but also very dry days). You can see its opposite if you run your A/C too cool down in the South of the U.S. during hot and humid summer days, where your cold interior causes condensation on the exterior of the windshield.