In the next two days, the first cold wave of the season can be seen in North India. The Meteorological Department has issued an alert in view of the possibility of cold wave in some parts of Punjab, Haryana and North Rajasthan. The Meteorological Department announces a cold wave when the minimum temperature drops below 10 degrees Celsius or 4.5 degrees below normal for two days. Cold wave is declared in the plains even when the minimum temperature is less than 4 degrees.
The minimum temperature in Delhi fell to 9.6 degrees on November 17 and 9.8 degrees on Sunday, with the temperature being 3 degrees below normal on both the days. According to RK Jenamani, there is a possibility of a drop in the minimum temperature in Delhi too, but there is no possibility of cold wave. However, cold wave may be recorded in Haryana and Punjab. The minimum temperature on Monday was 11.4 degrees. Hisar in Haryana recorded a temperature of 7.2 degrees Celsius on Monday, four notches below normal.
According to DS Pai, head of scientific and climate research and services at IMD Pune, there are two ways for the temperature to drop. One is the clear sky, due to which the heat from the surface returns rapidly. This is called Radiational Cooling. At present, the sky is clear in Northwest India.
The second reason for increasing cold is the flow of cold and dry north-westerly winds passing through the Himalayas. As soon as these winds reach the plains, the cold increases. Presently, a low pressure area has developed over the Arabian Sea which indirectly helps in the entry of north-westerly winds over the entire north-west region. This happens in winter. A continuous low pressure area has formed over the Arabian Sea.