Areas of Dense Fog for Portions of Our Region Today... As of 1130 AM, visibility across much of southeastern Pennsylvania is near or less than one quarter mile in fog. The lower visibility is being observed to the southeast of Reading and Allentown and just outside of Philadelphia. A Dense Fog Advisory is in effect until 2 PM where the lowest visibility is occurring. Other areas should see visibility mainly between one half mile and 2 miles, but be on the lookout for locally lower visibility in fog. When traveling in and around dense fog, use caution driving, take it slow, and give extra distance to the vehicle ahead of you. Use extra caution in areas where pedestrians are near roadways.