Why does it go foggy

Local Radar. Rivers and Lakes. Climate and Past Weather. Valley fog in Harrison County, Indiana. Scott Taylor Advection Fog Advection fog often looks like radiation fog and is also the result of condensation. Fog invading downtown Louisville from the Ohio River. WHAS Freezing Fog Freezing fog occurs when water droplets remain in the liquid state until they come into contact with a surface upon which they can freeze.

Freezing fog in Jefferson Memorial Forest. Tony Bright Evaporation or Mixing Fog This type of fog forms when sufficient water vapor is added to the air by evaporation and the moist air mixes with cooler, relatively drier air. Hail Fog Hail fog is an unusual type of fog that forms shortly after a heavy hailstorm. Hail fog along Interstate 65 near Horse Cave, Kentucky. Weather Story. Weather Map. Follow us on Twitter. Follow us on Facebook. Follow us on YouTube.

Disclaimer Information Quality Help Glossary. The droplets are what make fog visible, because water vapor, like all gases, is invisible. Fog develops in humid conditions, because there has to be a lot of water vapor in the air for it to form, National Geographic reports. Water vapor isn't the only thing that must be present, however.

Some type of air pollution or dust particles must also be present, because the water vapor condenses around the particles to form the fog. Sea fog, for example, which forms over oceans and other bodies of salt water, forms when water vapor condenses around salt in the air.

And one of the most dangerous types of fog, super fog, forms when water vapor combines with smoke from wildfires, causing an extremely dense fog, NOAA reports. This type of fog is sometimes so thick you can't see your hand in front of your face. Neither sea fog or super fog occurs locally.

Instead, we experience other kinds of fog, most typically radiation fog, which is also sometimes called ground fog. Radiation fog typically develops in the evening, when the heat absorbed by the ground during the day is radiated back into the air, causing fog to develop, National Geographic reports.

In colder temperatures, freezing fog or ice fog can develop. These two types of fog are different, but both occur in cold weather. Ice fog forms only at extremely cold temperatures and develops when the air at ground level is cold enough to turn the water in fog into ice crystals, according to NOAA. Freezing fog is similar to radiation fog, but it occurs when the water vapor forms ice crystals instead of water droplets.

In weather reports, we often hear that the fog will "burn off" by a certain time. That terminology is actually a misnomer, however. First, the air is cooled to the dew point which leads to the formation of fog droplets. When the air temperature is the same as the dew point temperature, condensation occurs on tiny particles floating in the air. The second method of fog formation requires water to evaporate from the surface into the air, raising the dew point until condensation occurs.

Fog often dissipates with daylight. When the sun rises, the air and ground warm up. This leads to the air temperature being warmer than the dew point temperature, which causes the fog droplets to evaporate.

As the nights are getting longer in autumn, we often have clear and cloudless skies at night.