It grows when the atmosphere becomes sufficiently unstable because of localised surface heating or other causes. ... If the atmosphere is unstable further, the cumulus cloud grows vertically to form cumulonimbus cloud and subsequently a thunderstorm, popularly known as nor'wester.

What causes Kalbaisakhi?

What is Kalbaisakhi? In India, a short-lived dusty squall at the onset of the southwest monsoon (April– June) in Bengal. It is attributed by Bn. Banerji (1938) to a cool dry upper current from the north or northwest meeting a shallow surface flow of warm air from the Bay of Bengal along a quasi-stationary front.

Where norwester is found?

Based on event descriptions and the meteorological environments involved, it appears that at least some "nor'westers" are, in fact, progressive derechos. During this time Odisha, West Bengal, Assam, Bihar, Chhattisgarh, Jharkhand, Bangladesh and North-Eastern states of India are affected by violent thunderstorms.