Context

According to Indian Metrological department, minimum temperatures in Punjab, Haryana, and the northern reaches of Rajasthan and Uttar Pradesh hovered around 6-9 degrees C

Dense fog: It is generally a thick white cloud that forms close to the land or sea. Temperatures should be lower and abundant moisture should be available near the surface.”

Mechanism: The land surface cooling down at nigh which also led the air close to the surface also cools down. As cooler air cannot hold as much moisture as warm air(supersaturation), the water vapour in the air condenses and form fog. 

 Condition for fog formations:

• Low temperature
• Abundant moisture near the surface
• High humidity(some instance where at lower humidity it may result in fog)