Northwestern Utah residents and motorists Friday had to contend with heavy fog and continuing stagnant air, often typical weather conditions for this time of year.

With heavy fog blanketing the area around the Salt Lake International Airport, visibility was down to zero Friday morning. Some aircraft were able to land and take off in the fog at the airport. Others weren't, said Craig Schmidt, a meteorologist at the Salt Lake office of the National Weather Service."The fog is as dense as it has been all winter at the airport," Schmidt said.

"It's a question for the individual airlines. It depends on instrument and pilot capabilities," Barbara Gann, spokeswoman for the Salt Lake Airport Authority, said.

Motorists encountered areas of dense fog in Utah, Cache, Davis, Tooele and other northwestern Utah counties.

One accident on westbound I-80 near the Great Salt Lake occurred about 5:45 a.m. Friday. It involved two trucks, one an empty semitrailer tanker and the other a cargo truck hauling powdered milk. Preliminary investigation indicates the accident was fog-related.

A Utah Highway Patrol dispatcher said there were no injuries and that traffic was not significantly affected due to the early hour of the accident. Stagnant air is blanketing the Wasatch Front, and a Class A health advisory is in effect for Utah County.

"Due to the air stagnation, the Utah Department of Health suggests that the non-essential use of motor vehicles be reduced," Art King, environmental health scientist at the state's monitoring center, said.

That applies throughout the Wasatch Front.