Climate of West Bengal
West Bengal has a tropical climate. The plains are hot except during the short winter season. The mountanious region in the north is cold. On account of its altitude but there humidity is high. The classical tradition speaks of six seasons-Spring, Summer, the rainy, Autumn, mild Winter and severe Winter. Only four clearly marked seasons with a brief interregnum of spring are observed, namely the hot season, the rainy season, the post monsoon season corresponding to autumn and the cold season. The hot season lasts from mid-March to mid-June, with the day temperature ranging from 38o C to 45oC in different parts of the state. At nights, a cool southerly breeze carrying moisture from the Bay of Bengal is usually present. The high temperature often causes troughs of low pressure to form on the plains which are compensated by sudden briefs storms known as kal-baisakhi or 'nor-westers', accompanied by thunder showers. These summer storms can be quite destructive. The hills of Darjeeling district are pleasantly cool in summer, the higher reaches are sometimes enveloped in heavy fog. On some days, one is rewarded by the sight of the majestic snow-girt Kanchanjunga and the eastern Sikkim ranges and the greenness of the wooded hills and gorges that abound on all sides.
The monsoon arrives by a middle of June. Its scouts start arriving about two weeks before its normal onset. This is called the Chhota monsoon which breaks the hot spell of summer. The monsoon rains in west Bengal are caused solely by the current of wind from the Bay of Bengal.
Variability is a characteristic feature of the monsoon in west Bengal as well as Bangladesh and Orissa which all receive the impact of the south-west Bay current. Breaks in the continuity of rain are not unusual, the resultant thoughts of low pressure develop into cyclone storms especially towards the end of the season and in early autumn.
A welcome change in the weather begins to be distinctly felt towards the end of September. Autumn in West Bengal is the season for festivity in the fields the golden grain of paddy starts ripening and is harvested towards the end of the season. The conclusion of the round of the festivities marks the onset of the winter in mid-November.
Winter, which lasts about three months, is mild over the plains, the average minimum temperature not falling 15o C. It is attended by a cold and dry northern wind, substantially lowering the humidity level. Winter is the season for the rabi crops-pulses, potato and vegetables and citrus fruits that grow on the Darjeeling hills. There occurs a short interregnum of clouds and rain usually the last week of December and the first week of January, caused by the incursion of the western monsoon coming all the way from the Arabian Sea. The cold is severe on the hills and there are sometimes sleet and snow on the higher reaches during the days of rain.
The weather gets warmer by the middle February, which heralds a brief spring season lasting about a month during which the deciduous trees break out in young green leaves and flowers. But this mellow season is too short-lived and the heat is turned on until with the coming of April, clammy summer comes in full blast and the annual cycle of seasons rolls on once again.