Fog is a natural phenomenon and is formed when water vapours in the air near the surface begin to condense into liquid water. Fog occurs over Punjab (Pakistan), during winter months of November, December and January. The aim of this study was to investigate the dense fog events and also to find the reasons of this prolonged fog. This prolonged/unusual fog affects the air and road traffic badly. Many accidents take place because of poor visibility and many people lose their lives. Using 30-year (1976-2005) real meteorological data of 10-weather stations, four dense fog years were investigated. Daily, ten-days and monthly temperature and moisture data of these four years showed significant changes during the fog events. It is observed that day time temperature decreases and night time temperature increases during fog events but the mean temperature remains below 15.5 degrees Celsius, mean relative humidity examined more than 80% for the north Punjab and more than 70% for the south Punjab and throughout the fog period,daily saturatain vapour pressure deficit found below 1hpa and with these conditions, dense fog events could be predicted precisely for next 24-48 hours.