The India Meteorological Department (IMD) announced on Monday that there will be more cold wave days than usual this winter in Delhi, Haryana, Punjab, eastern Uttar Pradesh, northern Madhya Pradesh, western Maharashtra, and Arunachal Pradesh. A 'cold wave' is defined by the IMD as a minimum temperature of 10°C or less in the plains and 0°C or less in hilly areas. Also, if temperatures drop 4.5°C to 6.4°C below normal, it counts as a cold wave day. IMD said, "The upcoming winter months from December to February are likely to be normal to below-normal minimum temperatures and are likely over most parts of central India, adjoining peninsular India, and northwest India, while above-normal minimum temperatures are expected in the remaining parts of the country. Cold wave occurrences are expected to be above normal over parts of central, northwest, and northeast India during the season." M. Mohapatra, Director General of IMD, explained that fewer western disturbances, which normally bring rain and raise minimum temperatures, are a key reason for longer cold wave spells. He added, "This is also a La Nina year (characterised by cooler temperatures in the Central Pacific). While there is no direct correlation, historically La Nina years tend to correlate with cold waves." Cold wave spells started unusually early this year, in November, due to the Polar Vortex — bands of very cold air that usually stay near the poles but sometimes move south. "The Himalayas protect India from the Polar Vortex, but we can feel some of its effects," Mohapatra said. He also noted that recent cyclones Senyar and Ditwah brought heavy rainfall causing damage, with Senyar being unusual for originating from the Straits of Malacca and Ditwah causing severe flooding in Sri Lanka.