How does fog form? Fog forms when the air temperature and the dew point temperature is less than 5 degrees apart. Fog begins to form when water vapor condenses to very small liquid droplets in the air. This occurs from either adding moisture in the air or when the air temperature drops.
The Break Down: Wednesday afternoon fog formed throughout Central Pennsylvania and cut down the visibility. So,what caused the fog to form Wednesday afternoon and why was it so thick?
A warm front brought steady and heavy rain to the region. The rain added more moisture into the air causing the air to become saturated. The dewpoint temperature and the air temperature were less than 5 degrees apart. This is a perfect setup for fog to form but what made the fog a bit thicker and more wide spread is the snow. The snow helps cool the surrounding air, allowing the dewpoint temperature and the actual air temperature to be very close to each other. This allows widespread and dense fog to form.