Kalbaisakhi

A kalbaisakhi (Bengali: কাল বৈশাখী /kaːl boiʃakʰi/, Odia: କାଳ ବୈଶାଖୀ /kaɭɔ̟ bɔ̟isakʰi/,), also known in Assam as a bordoisila (বৰদৈচিলা) and in some English publications as a nor'wester, is a localised rainfall and thunderstorm event which occurs in Bangladesh as well as the Indian states of Bihar, Jharkhand, Odisha, Tripura, Assam, and West Bengal during summer.

These storms generally occur in the afternoon or just before sunset, when thick dark black clouds start appearing over the sky and then bring gale-speed wind with torrential rain, often with hail, but spanning only a short period of time.

[3] Based on event descriptions and the meteorological environments involved, these storms can be classified as progressive derechos.

They gradually gain strength as they move southeastwards and impact the states of Odisha, West Bengal, and Assam with gale-speed winds (often exceeding 100 km/h (62 mph)), torrential rains, and hailstorms.

On some occasions, incursion of moist air in these elevated places, when combined with high surface temperatures, causes violent thunderstorms.