Areas of dense fog were expected to reduce visibilitiy below a quater mile in scattered locations this morning, according to the National Weather Service.
The wervice warned drivers to be prepared for "drastically reduced and rapidly changing visibilities."
The notice covered a wide area including the Pittsburgh metro area, Washington, Canonsburg, Donora, California, Charleroi, Monongahela, McMurray, Waynesburg, Greensburg, New Kensington, McMurray, Jeannette, Latrobe, Uniontown, Connellsville, Ohiopyle, Wheeling, Morgantown and the riges of Westmoreland and Fayette.
Some patches of fog persisted past 9 a.m today, particularly some of the smaller valleys, said National Weather Service meteorologist Lee Hendricks.
He said the fog was the result of warm moist air moving over cold surfaces, some of which are cold enough to be snow-covered.
there's still some patches of fog particualry in some of the smaller valleys and remnant of snow laying around.