Sky still hazy and a little warmer.

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We have seen patchy fog develop a few mornings this week, so let's look at how fog forms and why not everyone sees it. 

Fog is a collection of liquid water droplets or ice crystals suspended in the air at or near the Earth's surface. While fog is a type of cloud, the term "fog" is typically distinguished from the more generic term "cloud" in that fog is low-lying, and the moisture in the fog is often generated locally (such as from a nearby body of water, like a lake or the ocean, or from nearby moist ground or marshes). This is why communities near the Ohio River, small ponds, or other moist, low-lying areas have seen more fog this week.

There are several different types of fog and each forms a little differently, so today we will stick to the two most common types in our area and the ones that have likely caused the fog this week:

Radiation fog is formed by the cooling of land after sunset by thermal radiation in calm conditions with clear sky. This is a prime example of what this type of fog looks like in downtown Louisville.

Advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is most common at sea when moist air encounters cooler waters, including areas of cold water upwelling. This is most common here over the Ohio River or larger lakes.

Reach meteorologist Hannah Strong at HStrong@wdrb.com, on Twitter or on Facebook. Copyright 2022. WDRB Media. All rights reserved.