How and why does fog form? A meteorologist explains 🌫️

The science behind reduced visibilities in South Central Texas

A foggy morning in San Antonio. Photo Credit: Yvonne Scherny (Yvonne Scherny, KSAT)

Muggy mornings in South Central Texas can often consist of dew, a big can of hairspray, and at times another meteorological phenomena: fog.

We run into fog on the morning commute or drive to school, which can often slow us down.

There are several different types of fog, but how exactly does fog form?

To understand the answer to that question, we first need to talk about the air temperature and the dew point temperature.

Air Temperature vs. Dew Point Temperature

We all know the air temperature, which is essentially how hot or cold it is outside.

The dew point temperature, however, is another weather parameter that meteorologists use to represent the temperature that the air must cool down to in order to become saturated.

Higher dewpoints mean that the air is muggy and humid, while lower dewpoints mean that the air is drier and more comfortable.

As the air temperature cools down over the course of a muggy night, it starts to approach the dewpoint temperature.

The closer those two numbers are together, the more saturated the air around us becomes.

Similar to how a cloud forms above our heads, fog then starts to develop under these saturated conditions as water vapor condenses onto small particles in the air.

The result: reduced visibility out on the roadways!

Fog Safety

There are several safety measures that are important to follow when driving in the fog:

  • Slow down your speed and allow extra time to get to your destination
  • Use your low-beam headlights when driving

Leave plenty of distance between you and the vehicle in front of you in case of a sudden stop


About the Author:

Meteorologist Mia Montgomery joined the KSAT Weather Authority Team in September 2022. As a Floresville native, Mia grew up in the San Antonio area and always knew that she wanted to return home. She previously worked as a meteorologist at KBTX in Bryan-College Station and is a fourth-generation Aggie.