Not minus 4, but Delhi, north India will definitely shiver

North India is in the grip of a bone-chilling cold wave. Delhi has witnessed a record-breaking January. This year, it witnessed the third-worst cold spell in 23 years. The temperature dipped to minus 6 degrees Celsius in Kashmir. Similarly, there was dense fog in Amritsar and extreme cold in Churu. Predictions by the India Meteorological Department say the next few days will be colder.Why are temperatures set to fall again after the brief respite?Western disturbances regulate weather during winters in north India. These are low-pressure systems that carry a lot of moisture from the Mediterranean region. They go eastward and then to north India, and bring wet weather. If it is an active system, it brings wet weather and snow in the Himalayas and rains in the northern plains. When western disturbances approach this region, temperatures go up in the planes. This is what happened in the last three to four days — a western disturbance approached breaking the cold spell. Now that disturbance is leaving us and bringing the chill back. Therefore, there are forecasts of falling temperatures, especially from January 16.Will it be colder than early January? Will Delhi witness -4 degrees Celsius?I think minus 4 degrees is not going to happen in Delhi. The weather department has predicted cold waves in some parts of the city. The temperature is likely to fall around 3 degrees Celsius in many stations of Delhi and NCR. The minus 4 degrees Celsius prediction was not for Delhi. It was for parts of north India, especially like some regions in Rajasthan where temperatures really go down during peak winter. How long will the cold wave last?It will not last too long. From January 18, there will be a fresh western disturbance. When that happens, the wind direction changes from north-westerly to easterly. north-westerly winds are cold and icy during this part of the year, while easterly winds are warmer. But we could get another spell of relatively cold weather after January 20. Why did north India experience a record-breaking cold wave in early January?We had a prolonged cold-wave spell this year. That happens when we don't get an active western disturbance for a long period. Western disturbances are low-pressure systems that have moisture when they come into the region and break the cold spell. But this year, there weren’t too many active western disturbances. In fact, from December till now, we did not get an active western disturbance in north India. This is odd. In the absence of a western disturbance, especially when north-westerly winds are blowing, the weather becomes cold. If the cold spell is prolonged then the temperatures can really fall, as we saw this time.What is a cold wave? What are the core cold wave zones in India? A cold wave is when the minimum temperature is 4 degrees or more below the normal of that period in the region. Most of north India faces cold waves. But temperatures in northern plains, especially in parts of Rajasthan, Haryana, and some parts of Punjab can really fall. But a cold wave in, for instance, Bihar, would be different from a cold wave in Rajasthan. In Bihar, the temperature will not go really low.Since the normal temperatures in Bihar, West Bengal, Odisha, and other such places in East India do not dip too low, a cold wave would mean that it is colder than usual. But it will not be freezing as in Rajasthan, Punjab, Delhi, Haryana, or Western Uttar Pradesh. On Friday, Fatehpur in Rajasthan witnessed a record minus 3.5 degrees Celsius. Audio Production: Sahil Gupta