Using 30-year (1976-2005) real meteorological data of 10-weather stations, four dense fog years (1998-1999, 1999-2000, 2001-2002 and 2002-2003) 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 saturation vapour pressure deficit found below 1 hPa. The synoptic charts for these years showed that moist currents continuously penetrate into Punjab from Bay of Bengal and a trough forms over this region. At the same time a high pressure area develops near the foot of Himalayas. Similarly, 850 hPa charts revealed that a trough persists over this area and also a ridge is present to the north east of this region. This work would be helpful to understand the reasons of fog development during winter season in Punjab and to predict the phenomenon before time to minimize the impacts on daily public life and agriculture.