Sunday, September 13, 2009


The morning sun warmed the moist air rising from the melting snow of the Stockton Plateau. Particulates not usually found in this region had been swept in by the storm. Now the particulates enhanced condensation of the air just above the ground as the snow lost its whiteness in a great gray blanket that covered the land.

Fog is a cloud that touches the ground. Water vapor, a colorless gas, becomes visible when it condenses and forms tiny water droplets. The gas turning into liquid or the water vapor becoming water is the visible spectrum that the human eye detects. The density of this air and water combination is the key to determining whether scientists consider it fog or mist. Fog reduces visibility to less than 1km while mist reduces visibility to I KM or more.

The temperature difference between the dew point or condensation point and the ambient air temperature is usually reduced with colder temperatures. Fog most often occurs when this temperature differential is less than 4 degrees Fahrenheit.

The process of water vapor turning into water droplets occurs in saturated air with a relative humidity of 100 per cent but can be less when particulates especially hygroscopic or water seeking particles like carbon emissions produce a condensation nuclei that enhances water vapor to condense at a lower relative humidity.

The foggiest places in the world are not found in the Trans-Pecos, but occasionally when storms or fronts sweep in wet cold air along with particulates from pollution sources such as vehicles and smoke stacks, together with other naturally occurring aerosols like soil dust lifted up from wind, the combination can increase the possibility of fog.

Fog on the California coast in Marin County occurs an average of 200 days per year where cooler dry land air meets the wetter warmer air above the Pacific Ocean. It is now believed that the sea weed known as kelp emits iodine particulates producing the condensation nuclei that enhances fog to form in air with less than 100 per cent relative humidity.

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