DETROIT – If you have a craving for fish and chips, perhaps it’s because the weather in Detroit has looked more like London the past few days. Dense fog continues to reduce visibility, and it’s not going away anytime soon.
So what is fog? Fog is basically a cloud that sits on the ground.
In winter, fog often shows up in a few common ways:
- Radiation fog forms on clear, calm nights when the ground loses heat, chills the air touching it, and that air reaches saturation.
- Advection fog forms when mild, humid air moves over a colder surface, like snow, ice, or frozen ground, and cools from below until it becomes saturated.
- If the air is below freezing, droplets can freeze when they touch roads, trees, and power lines. That’s freezing fog, and it can leave a thin coating of ice.
Metro Detroit has extra “fog fuel” because we’re close to water like the Detroit River, Lake St. Clair, and Lake Erie. When winds are light and blow in from the lakes, moisture can build up in the lowest layer of air. High humidity and light winds are drawing fog off Lakes Erie and St. Clair helping the setup for fog around Detroit.
We’ve also had damp, mild stretches this winter. Rain, drizzle, and melting snow leave the ground wet, which adds moisture back into the air, especially at night. The saturated ground, melting snow, and light winds helped keep fog and low clouds from lifting, and visibility dropped to a quarter mile or less at times. A Dense Fog Advisory is used when widespread fog reduces visibility to 1/4 mile or less.
Fog usually fades once drier air arrives, winds pick up, or sunshine warms the ground. Weekend sunshine and colder air will make for a less foggy forecast.