The year can be divided into the following four seasons on the basis of the monsoon variations.
1. The cold weather season : The cold weather persists from December to February throughout India. January is the coldest month. Temperature is between 10º C to 15ºC in northern plains and 25ºC in southern parts of the country. There is high pressure in northern plains due to the cold climatic conditions. The cold dry winds blow from the high pressure towards the low pressure equatorial regions. These winds are north westerly in the Ganga plains and north easterly over the Bay of Bengal. Only two parts of the country receive rain in this season. First is the north west part of India which receives rainfall from the Mediterranean cyclone. Second is the coast of Tamil Nadu which gets rainfall in winter.
2. The Hot Weather Season : During this period there is a rapid shifted belt of heat from south to north. In May, the rising temperature leads to a low pressure in a wider area from the Thar desert to Chhota Nagpur. Because of this low pressure, the moisture laden winds from the Arabian Sea are attracted toward this area and consequently there is rain fall.
Kerala and Western Ghats also experience the pre monsoons showers. Assam and Bengal also receive some rainfall by means of evening thunderstorms. But the north west remains dry and hot winds called the loo, engulf the whole area. Sometimes dust storms in Punjab, Haryana and U.P. are followed by light rain and cool breeze.
3. Advancing Monsoon Season : This season runs from June to September. During these months the south west monsoon winds blow northwards into two branches from the Arabian sea and the Bay of Bengal. They make rainfall almost in the whole of northern India. These winds blow from the oceanic high pressure area towards the low pressure area of land and make heavy rainfall. The Arabian sea branche causes heavy rainfall in the coastal areas of the Western Ghat but this rainfall decreases as the monsoon goes further. Kutch receives less rain fall. The Bay of Bengal causes heavy rain fall in the hills of Meghalaya. Mawsynram receive highest rainfall in the world As the monsoon winds take a turn from east to west because of Himalayas, the rain goes on decreasing. Due to the uncertainty and uneven distribution of rainfall, floods and droughts are common during this season.
4. The Retreating Monsoon : This season runs from October to November. At this time the monsoon start retreating. The lower temperature on the plains gives rise to gradual increase in pressure and as such the monsoons retreat from most parts of North India. Depressions originate in the southern part of the Bay of Bengal and start moving towards the east coast of India. Tamil Nadu receives high rainfall from these winds during this season. The distribution and the range of rainfall is not certain even during this season.
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