CHICAGO (WBBM NEWSRADIO) — For the second straight day in Chicago dense fog blanketed the city, obscured the skyline and made the sun feel about as far away as it’s been all month.
To help spell out how such a heavy fog comes together, the team over at AccuWeather sat down to answer a few questions from WBBM. Check out their responses below, and of course, be sure to tune in to WBBM Newsradio’s live weather updates on the 8’s for the latest updates.
Editor’s Note: AccuWeather’s responses have been lightly edited for clarity.
WBBM: We’re on Day Two of intense fog in Chicago; help us understand what factors drive foggy weather.
AccuWeather: Fog happens when the temperature and the dew point — or, the measure of how much moisture in the atmosphere — become equal. That can occur in different ways.
Much of this fog is being caused by warmer and moist air above the ground, which has been pushing over the cold ground. That, in turn, lowers the temperature of the air. Once the dew point and the temperature get to be equal, fog forms.
WBBM: How does Chicago’s proximity to Lake Michigan affect our fog?
AccuWeather: Being near the lake can be impactful to fog, especially when the land is warmer and the lake temperatures are cooler. That’s important because any wind off the lake is bringing those cooler temperatures over the land, which can affect or push fog off the lake into our region.
Lake Michigan likely isn’t to blame for the heavy fog we’ve seen in recent days, though. This is more from the warmer air pushing in from the south over the colder ground.
WBBM: It feels like a big cloud just fell on Chicago. Is that basically what fog is? A big cloud that’s closer than normal?
AccuWeather: Absolutely. When someone tells you to keep your head out of the clouds on a foggy day, you can’t — because that is what fog is. It’s essentially a cloud at ground level.
Sometimes those clouds hang just above the surface, so we call those low clouds and patchy fog. Other times, that cloud comes right to the surface, which results in thick, dense areas of fog that are misty in between. It’s what it would feel like to walk in the clouds —they just happen to be at the surface
All Chicago-area counties will be under a National Weather Service Dense Fog Advisory until 6 p.m. Thursday.
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