Occurrence of weather is governed by the wind pattern. Be it the temperature, clouds, precipitation or any other weather parameter, prevailing winds have dominant role to play. In short, human comfort/discomfort are largely dictated by surface and low level winds. Along with the horizontal motion of the winds, the vertical motion is very important. Vertical motion in the atmosphere is rather small. The order of scale is few millimeters per minute and can not be measured directly. In spite of their small magnitude, vertical velocities are very essential in causing clouds and rain.
In the winter season (Dec to Feb) the winds are mostly west to north westerlies over North India, easterlies over Northeast India, variable over Central India and east to northeasterlies over peninsular India. Prevalence of normal winds over the respective zones is an indication of good weather conditions except over South India where because of the northeast monsoon; northeasterlies could prevail both during good as well as bad weather days with small variations.
North and Northeast India
The presence of anticyclone (clockwise winds) in the lower levels over Rajasthan results in northwesterlies over the plains. Change over to easterlies is indicative of approach of the weather in some form or the other. Prevalence of easterly winds over the northern plains are suggestive of increase in humidity, drop in day temperature, rise in the night temperature, drop in the visibility and possible occurrence of rain in the plains and snow over the hills. Conversely, easterlies over Assam valley and neighbourhood are indicative of clear and fair skies, while westerlies attached with marginal weather conditions are likely to affect air operations.
Variable winds over central parts of the country are associated with prominent change in the temperatures, particularly over Vidharbha, Marathwada, Chhattisgarh and Telangana region. Confluence zone of northwesterlies from the plains and easterlies as a part of North East monsoon penetrating up to these areas lead to a rapid drop or rise in temperatures.
Winds over peninsular India remain northeasterlies / easterlies barring west coast where the setting of sea breeze in the afternoon brings in reversal of wind towards the later part of the day. Winds over the east coast always remain from the east, irrespective of the time. The west coast observes easterlies during late night and morning and westerlies in the afternoon and early night. Therefore, maximum temperatures along the west coast are mostly a shade higher than the east coast during these months.