Winter Weather Alert Warns Drivers of 'Freezing Fog'

The National Weather Service urged drivers to take extra caution after reports of freezing fog in parts of Wyoming early Thursday morning.

According to the National Weather Service (NWS), freezing fog occurs when tiny supercool liquid droplets freeze instantly on exposed surfaces—including tree branches, stairs, sidewalks, roads and vehicles—when surface temperatures are at or below freezing. The phenomenon can cause black ice, which is more difficult to see, to form along roadways, creating hazardous travel conditions for drivers.

Michael Musher, a public affairs specialist and meteorologist for the NWS, told Newsweek on Thursday morning that freezing fog is "not necessarily uncommon" and is more likely to occur during the late fall, winter and early spring.

Reports emerged about areas of freezing fog along Interstate 80 near Rawlins, NWS wrote in a special weather alert at 3:44 a.m. MT. Visibility down to a quarter-mile has been observed in the area, the alert said.

The alert warned drivers to use caution when driving in the area as roads may become slick, particularly on bridges and overpasses. The NWS has previously urged drivers to drive more slowly during conditions such as freezing fog.

Newsweek reached out to the NWS and Carbon County Department of Emergency Management via email for comment.

Carbon County is in southeast Wyoming and consists of roughly 14,500 people, according to U.S. Census data. Rawlins is its largest city and county seat. Temperatures in Rawlins were expected to reach a low of 18 degrees Fahrenheit on Thursday night, according to the NWS.

Areas across the country, including various parts of the Mountain West, braced for snowstorms this week. The NWS issuing advisories and watches concerning snow and strong winds for parts of Alaska, Colorado, Michigan, New York, New Mexico and Wyoming earlier this week.

Officials also issued a winter storm warning for eastern states including New Hampshire and Vermont last weekend.

Other areas of Wyoming also recently experienced freezing fog. The NWS issued a freezing fog advisory for Cheyenne, the state's largest city, that expired Tuesday. The NWS also issued a freezing fog warning for Fremont County, north of Carbon County, in late November.

Freezing fog has created problems for drivers in the past. Experts said the fog was a major factor in a 30-car crash involving a dozen semi-trucks in Washington state in December 2022. Three people suffered non-life-threatening injuries in the crash, which occurred near Kittitas Valley.

The phenomenon can also potentially disrupt air travel, as it can cause a thin layer of ice to form on aircraft, making it "very dangerous" to fly unless the aircraft is treated or uses de-icing equipment, according to the NWS.

The fog most commonly occurs on mountaintops and in Arctic regions, according to the Farmer's Almanac.