Shallow to moderate fog has occurred in many parts of Bihar and West Bengal since last 2 days. Now we expect that intensity and spread of fog will increase and will cover more areas of Bihar and West Bengal. Parts of northeastern states of India are also likely to witness fog.
The reason for this fog is the difference in the temperature of Earth surface and wind blowing over it. The winds over East India are expected to start blowing from east direction. These easterly winds are slightly warm and humid in nature.
At present due to absence of any weather system the sky is clear over East India therefore the earth’s surface cools down rapidly leading to fall in night temperature.
When warm and moist winds from east direction blows over earth’s cool surface, the available moisture in the air tends to form fog. This type of fog is known as Advection Fog: such fog forms when warm, moist and stable air is blown across a cooler surface (land or water); the air temperature falls until the dew point is reached and condensation occurs.
Moreover a low pressure system which is expected to form over south central Bay of Bengal will be instrumental for the easterly winds to blow over most parts of East India. We expect this type of weather condition to go on for next 3-4 days.
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