<P> Western disturbances, specifically the ones in winter, bring moderate to heavy rain in low - lying areas and heavy snow to mountainous areas of the Indian Subcontinent . They are the cause of most winter and pre-monsoon season rainfall across northwest India . Precipitation during the winter season has great importance in agriculture, particularly for the rabi crops . Wheat among them is one of the most important crops, which helps to meet India's food security . An average of four to five western disturbances form during the winter season . The rainfall distribution and amount varies with every western disturbance . </P> <P> Western disturbances are usually associated with cloudy sky, higher night temperatures and unusual rain . Excessive precipitation due to western disturbances can cause crop damage, landslides, floods and avalanches . Over the Indo - Gangetic plains, they occasionally bring cold wave conditions and dense fog . These conditions remain stable until disturbed by another western disturbance . When western disturbances move across northwest India before the onset of monsoon, a temporary advancement of monsoon current appears over the region . </P> <P> The strongest western disturbances usually occur in the northern parts of Pakistan, where flooding is reported number of times during the winter season . </P> <P> Western disturbances start declining in numbers after winter . During the summer months of April and May, they move across north India . The southwest monsoon current generally progresses from east to west in the northern Himalayan region, unlike western disturbances which follow a west to east trend in north India with consequent rise in pressure carrying cold pool of air . This helps in the activation of monsoon in certain parts of northwest India . </P>

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