* WHAT. Visibility 4 to 5 miles in dense fog. * WHERE. Portions of northern Tennessee valley and southwest Virginia. * WHEN. Until 9 AM EDT this morning. * IMPACTS. Dense fog has developed in river valleys and low elevation areas across the northern Tennessee valley and southwest Virginia this morning. This will create hazardous driving conditions until it dissipates.

Fog will persist throughout the night, mainly in the valleys, and will be locally dense in spots. It will dissipate for most impacted areas by 8am or 9am this morning. Motorists should use caution and be prepared for sudden changes in visibility. Keep greater distance between vehicles, use low beam headlights, and allow more time to reach your destination safely.

Mostly clear skies, light winds, and lingering low-level moisture are helping areas of valley fog to develop and become dense early this morning. This fog will continue to expand through the night but likely remain thickest in the valleys. Visibilities will be below a quarter of a mile at times in the densest areas of fog. Be sure to slow down and use your low beam headlights when you encounter any fog.