Kalbaisakhi

Nor'wester in Kolkata, India, 2010

Nor'westers or the Kalbaishakhi(କାଳ ବୈଶାଖୀ), mostly referred in Odisha or Bordoisila or Bardoli Chhera an isolated rain fall and thunder storm which occurs in India and Bangladesh, often with violent hurricane-speed winds. If given enough moisture and convection currents, it can even take the form of tornadoes (such as the Bangladesh Daulatpur-Saturia tornado on April 26, 1989). These generally occur just before sunset or just few hours after it, when thick dark black clouds start appearing over the South Western sky and then bring gale-speed wind with torrential rain often with hail but span only a short period of time. Kalbaishakhi or Bordoisila occurs, with increasing frequency, from March till monsoon establishes over North-East India. 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. They cause considerable damage to life and property and are known as Kalbaisakhi or the calamity of Baishakhi( in Odisha and West Bengal) or Bordoisila ( in Assam), the month of March–May in India. Kalbaishakhi or Bordoisila is accompanied by strong squalls and sometimes by hail. On extremely rare occasions, tornados may also accompany them too. Flying through these winds can be extremely dangerous. Circumnavigating or penetrating them may be disastrous and pilots avoid them. However, the rainfall in these storms is beneficial for the tea cultivated in Assam and for the jute and rice and tea cultivated in West Bengal and Bangladesh.They generally move from West to East.

A severe Nor'wester lashed through Dhaka and northwestern region of Bangladesh late April 4, 2015, leaving at least 24 people dead and hundreds injured. Weather officials said this was the first severe storm in the usual spring storm season. It left a tail of destruction uprooting hundreds of trees and flattening many tin built houses and mud-built houses and snapping road and rail communication with affected areas.