Symptoms
- Outside of windshield or windows fog up, usually in early morning or humid weather
- Wipers smear it around instead of clearing it
- Happens especially right after parking with the AC recently used
- Inside of the glass is dry and clear
Likely causes
- CommonHumid outside air condensing on cooler glassThe glass surface is colder than the surrounding humid air, especially after AC cooled it, so moisture condenses like dew.
- CommonOvernight temperature drop with high humidityClassic dew-forming conditions on a parked car, same as on grass or a windshield in the morning.
- Less commonWax or coating buildup on glass making water bead unevenlyDoesn't cause fog itself but can make it look worse or clear unevenly with wipers.
What to do
- Turn on the AC and point vents at the windshield; cooling and drying the glass from inside speeds up clearing the outside fog as temperatures equalize.
- Use the front and rear defrost/defog settings, which often include a slight heating element for the glass.
- Run the wipers with washer fluid rather than dry wiping, since dry wiping smears the condensation instead of clearing it.
- If it's a recurring morning issue, park facing away from direct exposure to open sky/high humidity areas when possible, or use a windshield cover overnight.
- Clean the exterior glass with a proper glass cleaner if water beads unevenly, which can make fog look worse than it is.
When to call a pro
This is a normal weather phenomenon and rarely needs a mechanic; if it happens even in dry weather with no humidity, have the glass and any coatings checked.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.