(CHICAGO)  An ice storm is expected to move through the Chicago area Tuesday evening, threatening to drop almost a half inch of ice and make travel nearly impossible on untreated surfaces.

Ice could total one-tenth to four-tenths of an inch, the National Weather Service said in an Ice Storm Warning. The highest amounts of ice are expected north of Interstate 55. The warning lasts from 6 p.m. Tuesday to 6 a.m. Wednesday.

Freezing rain will likely start after the evening commute at 8 p.m., but there’s a slim chance freezing rain could begin at 5 p.m., the weather service said. Some snow and sleet may mix with the freezing rain early in the evening.

The weather service strongly discouraged traveling during the storm. Snapped power lines and falling tree branches are also possible.

True ice storms are uncommon in this part of the county, the weather service wrote on Facebook.

“However, we are concerned that there is at least some risk for some areas to see the most significant accumulation of ice that they’ve seen in several years,” the weather service said.