Bangladesh is called the land of six seasons (Sadartu). It has a temperate climate because of its physical location. Though the climate of Bangladesh is mainly sub-tropical monsoon, ie warm and humid; Bangla calendar year is traditionally divided into six seasons: Grisma (summer), Barsa (rainy), Sarat (autumn), Hemanta (late autumn), Shhit (winter) and Basanta (spring). Each season comprises two months, but some seasons flow into other seasons, while others are short. Actually, Bangladesh has three distinct seasons: the pre-monsoon hot season from March through May, rainy monsoon season, which lasts from June through October, and a cool dry winter season from November through February. However, March may also be considered as the spring season, and the period from mid-October through mid-November may be called the autumn.
Winter (shit) The fifth season and the colder part of the year, in contrast to Summer, the hotter. According to the Bangla calendar it spreads over the months of Paus and Magh (mid-December to mid-February). But practically, November through February is the winter season in Bangladesh. Average temperatures in January vary from about 11’C in the northwestern and northeastern parts of the country to 20’C to 21’C in the coastal areas. Northern Bangladesh is cooler than southern Bangladesh, with occasional cold spells that claim lives. During this season, a centre of high pressure lies over the northwestern part of India (Himalayan zone). A stream of cold air flows eastward from this high pressure and enters Bangladesh through its northwest corner. During this season, winds inside Bangladesh generally have a northerly component (ie, flowing from north or northwest).
The winter season is very dry, which accounts for less than 4 percent of the total annual rainfall. Average rainfall during the season varies from less than 2 cm in the west and south to slightly over 4 cm in the northeast. Rainfall in this season is caused by the wind coming from the Mediterranean region that enters the country from the northwestern part of India along the Ganges basin. Rainfall amount is slightly enhanced in the northeastern Bangladesh by the orographic effect of the Meghalaya Plateau. These rainy spells bring the temperature down. The nights are longer than the days and mornings are often foggy. This is the time when deciduous trees shed their leaves.
Winter is the best and most enjoyable season of Bangladesh. A large variety of vegetables are available in the markets. So is fish, particularly large koi, magur, shing. Special flowers of the season are Ganda and Suryamukhi. Boroi (jujube) and oranges are among the fruits of this season. Date juice is extracted during this time, to be used as juice or made into gud (molasses). This is the season for pitha or rice cakes such as bhapa pitha, chitai pitha, patisapta and puli pitha. Source: http://en.banglapedia.org/index.php?title=Season
The seasons of Bangladesh regulate its economy, communication, trade and commerce, art and culture, and, in fact, the entire lifestyle of the people.