Dense fog is expected to continue in the Chicago area as warmer air settles in the area, according to the National Weather Service.
A dense fog advisory has been in effect on-and-off all week and was extended until 6 p.m. Thursday through much of northern Illinois and northwest Indiana, the weather service said.
The fog could reduce visibility to a quarter of a mile or less, the service said. Low visibility could cause hazardous driving conditions, and drivers are asked to slow down, make sure to turn on headlights and keep watch for slick spots on the roads.
Dense fog happens when a warmer air pattern travels over a cold ground, and the snow seen in much of the state is conducive to the heavy fog, according to weather service meteorologist Casey Sullivan.
“Oftentimes what will happen is if the air is warm enough, it’ll melt the snow and you won’t have that fog anymore,” Sullivan said, adding that the air mass seen this week hasn’t been warm enough to melt the snow quickly.
Rain is expected in the late afternoon Thursday, which could improve visibility and clear out some fog, according to Sullivan. Fog can happen for days at a time, similar to a pattern of extreme cold like the Chicago area saw last week, he said.
“While it might be uncommon, it’s not record-breaking or unheard of to have several days of dense fog,” Sullivan said.
Temperatures will continue to hover in the 30s through the rest of the week and conditions should begin to dry after Thursday’s rain, weather service meteorologist Jake Petr said.
