On Saturday, Delhi recorded a maximum temperature of 13.3 degrees Celsius and a minimum of 2.4 degrees Celsius. On the same day, Shimla and Mussoorie recorded maximum and minimum temperatures of 14.8 and 4, and 14.1 and 3.9, degrees Celsius, respectively. Simply put, Delhi and other areas in the north Indian plains have been recording temperatures lower than those in hill stations. Add to that, the maximum temperature in Delhi took a big tumble on Monday, settling at 9.4 degrees Celsius, making it the coldest December day since 1901—over a century. The minimum temperature at Palam was 2.9 degrees Celsius, Lodhi Road was 2.2 degrees Celsius, and Ayanagar 2.5 degrees Celsius. However, according to Times of India, a respite is expected in the coming days as the wind direction is likely to change on Monday when warmer easterly winds are expected in the region.
For the past weeks, frigid conditions persisted across the Indo-Gangetic plains, and northern India in general. Churk in Uttar Pradesh recorded 0.8 degree Celsius. Muzaffarnagar recorded a low of 1 degree Celsius, followed by Kanpur (1.6 degree Celsius), Agra (1.9 degrees Celsius), Jhansi (2.2 degrees Celsius), Varanasi (2.3 degrees Celsius) and Meerut (2.5 degrees Celsius). State capital Lucknow recorded a minimum temperature of 6.7 degrees Celsius, one notch below normal.
In Haryana, minimum temperatures hovered close to the freezing point at some places on Sunday. On the same day, Rajasthan capital Jaipur's minimum temperature settled at 1.4 degrees Celsius—the lowest in more than five decades. Faridkot in Punjab was the coldest place in the state, recording a minimum temperature of 0.7 degrees Celsius, six notches below normal limits. Among other places in Punjab, freezing cold swept Amritsar, which recorded a low of 1.2 deg C, Ludhiana, Patiala and Gurdaspur recorded near similar below normal minimums at 4.6, 4.5 and 4.2 degrees Celsius.
The causes of the cold wave
The factors responsible for such a cold December are a "very long spell" of icy winds and a layer of fog lingering over vast swathes of the northern plains for 10-12 days. Mahesh Palawat, Vice President (Meteorology and Climate Change) of Skymet Weather, told PTI the continuous flow of icy cold winds from the western Himalayas have not stopped in the past 10 days. "This is an unusual phenomenon. Usually, there is a western disturbance which helps break the cold wave spell but this did not happen in last 10 days," Palawat said. Western disturbance is a cyclonic circulation that originates in the Mediterranean Sea and brings rains over northwest India.
In a nutshell: Western disturbances in early and mid-December, as per its usual trajectory, led to heavy snowfall in hilly areas north of Delhi and frigid winds blew from there. But, in a gap of three to four days, another western disturbance was expected, as a result of which the wind direction changes. This time, the cold winds continued unhindered for over 10 days in the absence of a strong western disturbance.
Dense fog across the Indo-Gangetic belt, which hindered sun rays from reaching the ground, also aggravated the situation, according to experts. In the hills, the sun rays are able to penetrate the fog and helps clear the sky. With the sun rays reaching the ground, the temperature rises despite the chill. The density of fog increased this year as the flow of warm easterly winds began at a time the northerly cold winds already existed, Mrutyunjay Mohapatra, Director General of the India Meteorological Department (IMD), told PTI.
L.S. Rathore, former director general of the IMD, said fog factors differ in the hills and the plains. "The rays hit the hills first and there is more scope for the fog to dissipate. So, the temperature in the hills settles down after sunrise. On the contrary, in the plains, it becomes difficult for the rays to penetrate through fog. This is why the Indo-Gangetic belt is cold throughout the day."
Flight operations disrupted in national capital
Dense fog played havoc with flight operations at the Delhi airport on Monday with around 530 flights delayed, 40 cancelled and 21 diverted. Flights are operating at the airport under CAT III B conditions, which means the runway visual range (RVR) is between 50 metres and 175 metres. Giving an update on flight operations, an official said 21 flights have been diverted and around 40 cancelled as of now. "Around 530 flights—which includes 320 departures as well as 210 arrivals approximately—have been delayed on Monday," the official added. In a statement, IndiGo airline said,"Owing to dense fog in north India our flights have been impacted across India. We will continue to review the situation and provide real time updates on our social platforms." The airline also requested passengers to check flight status before leaving home and reach out to its customer care. Vistara airline said on Twitter that its Delhi-Mumbai flight UK933, as well as Mumbai-Delhi flight UK996, stands cancelled due to poor visibility in Delhi.
-Inputs from PTI