Dust storm is nothing but force of wind which disturb the ground dust and raise it vertically up to 2 to 4 kilometer. It reduces the horizontal visibility. At different places causes are different. Over North West India it is because of dry thunder storm. Locally it is called Andhi. There are two type of dust storm over North West India.
(1) Convective type :- In this case due to intense heating or due to induced cyclonic circulation of Western Disturbance and instability in the atmosphere, Cumulonimbus (CB) cloud develop.
“Cumulonimbus are huge turbulent clouds extending upto 15 to 20 kms upward. Lightning and thunder occur in these clouds.”
If moisture content is negligible then downdraft of Cb raise the dust up to two to three kilometre reducing the horizontal visibility less than one kilometre. Duration of phenomenon is one hour or less than one hour.
(2) Pressure Gradient type :- During the later part of the pre monsoon season an intense heat low develop over North West India. On some occasion a pressure gradient develops to south of this heat low. This strong pressure gradient gives rise to the strong wind both at surface level and at lower level up to 1.5 kilometer above mean sea level. This strong wind raise the dust and sand reducing horizontal visibility to less than one kilometre. These storms are of few hours to half a day or even some time more. Upper level divergence will increase the activity.
During the 3rd May 2018 storm occurred over North West India was of first type that is convective type.