Weather Warnings Issued for 28 States as 100 Million People Impacted

Dense fog blanketed more than half of the United States on Thursday morning, prompting the National Weather Service (NWS) to issue a slew of advisories as 100 million people were impacted in 28 states and in Canada.

“Unusual” dense fog covered nearly the entire span of the U.S. earlier this week, extending from the Canadian border in Montana to the Gulf Coast in Texas only a week after an arctic blast plummeted temperatures in many states to subzero levels. When a subtropical jet stream brought more moisture up from the south, it created advection fog, which caused the dense fog across many states.

NWS Weather Prediction Center meteorologist David Roth previously told Newsweek that this type of fog occurs when warm air condenses as it passes over colder ground.

The fog was expected to stick around throughout the week, and it impacted 100 million people in the U.S. and Canada on Thursday morning, AccuWeather reported.

“Over 100 million people are under fog advisories this morning in the U.S. and Canada, likely a 20-year record high,” AccuWeather posted on X, formerly Twitter, on Thursday morning. Photos of the dense fog in Cincinnati, Ohio; Nashville, Tennessee; Dallas, Texas; Oklahoma City, Oklahoma and several other cities accompanied the post.

Newsweek reached out to AccuWeather via email for comment.

Visibility was reduced to a quarter mile or less in many areas, prompting the NWS to issue a warning for motorists attempting to drive through the dense fog.

“Low visibility could make driving conditions hazardous,” one warning said.

Another warning advised mariners to exercise caution, as well.

“If you must navigate, proceed with caution. Use proper fog signals. Make sure all running lights are on. Remember to use your radar and compass,” the warning said.

Fog is not uncommon in January, particularly along the Gulf Coast as water temperatures drop. However, Roth called the extent of the dense fog on Tuesday an “unusual” occurrence.

The fog comes as unseasonably warm temperatures grip the eastern third of the U.S. Seven states faced record-breaking temperatures, with forecasts anticipating the lows could be as much as 50 degrees above average.

Rain accompanied the springlike weather, heightening flood risk in several states across the Mississippi Valley earlier in the week. One Texas city received nearly 12 inches of rain in a 72-hour period.

The abrupt shift in weather also is causing ice jams as river ice thaws and then begins to move. The chunks become stuck in piles near bridges or river bends, which causes the river to flood.