Creepy fog at the beginning of Halloween

Dense fog settled over Chicago early Monday to kick off Halloween, according to the National Weather Service.

But luckily for the trick-or-treaters, the fog and rain will clear by 10 a.m., although fog may persist in places until midday.

“That fog should stick around here for at least the next couple of hours before it gradually tapers off as we head into the afternoon,” said meteorologist Todd Kluber.

Visibility will be less than a mile, so forecasters are warning drivers to increase their following distance, reduce speed and use low beams during morning commutes.

For those who plan to spend a lot of time outside, temperatures will be mild in the low 50s to low 60s in the afternoon and low 50s in the evening.

[ Halloween weather in Chicago: The warmest, coldest, snowiest and wettest since 1871 ]

“It looks like most of the subway should be clear by, say, four or five o’clock. And by clear I mean no precipitation, maybe just a little rain that lingers,” Kluber said.

The only exception, he added, will be the extreme southern suburbs and northwest Indiana, where showers could last until about 6 or 7 p.m.

adperez@chicagotribune.com