Breakdown: Why fog forms early in the morning

Breakdown: Why fog forms early in the morning

MEMPHIS, Tenn. (WMC) - Foggy mornings are common in the Fall and winter in the Mid-South. There are several reasons why fog typically develops early in the morning.

Fog is made up of many very tiny water droplets or ice crystals. When the air close to the ground is cooled, water vapor condenses into tiny liquid water droplets, which are suspended in the air. This can occur because of added moisture or falling air temperatures. In simplest terms, the dew point (a measure of moisture) must be equal to the temperature for fog to form.

The lowest temperatures occur early in the morning, usually between 5 and 7 am. This means that the temperature will drop closest to the dew point temperature during this time. In addition, the relative humidity rises as the temperature drops, so there is more moisture availability for condensation to occur. With longer nights in the Fall and Winter, there is more time for this process to occur.

Not only does fog form in the morning, it also usually clears quickly in the morning too. Once the sun comes up, it heats the ground and raises the temperature. This brings the temperature away from the dewpoint and causes the fog to mix out.

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