Nor'westers or the Kalbaishakhi (Bengali: কাল বৈশাখী) (Odia: କାଳ ବୈଶାଖୀ), Bordoisila as known in Assam, are localised rainfall and thunderstorm event which occurs in Bangladesh and Indian states of Bihar, Jharkhand, Odisha, Tripura and West Bengal often exceeding 100 km/h (62 mph). These storms generally occur in 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.