Strong winds clear the air, western disturbance all set to bring back the chill

Just a day after Delhi reported “severe” air quality, for the sixth time since New Year, strong winds came to the rescue and dispersed the accumulated pollutants, thereby allowing the air quality index to touch the considerably better ”poor“category.

India Meteorological Department (IMD) has forecasted that winds will continue to blow at high speeds on Thursday as well, allowing for a further improvement in air quality. Also, a fresh western disturbance is likely to affect the western Himalayan region from January 22, causing widespread rain and snow in those parts between January 22 and 24,and a resultant chill in Delhi and other cities in the plains, the IMD has said.

The Central Pollution Control Board (CPCB) recordings show that on Wednesday, the overall air quality index of Delhi was 283, in the ”poor” zone. This was a major improvement from Tuesday, when the AQI was 404, in the ”severe” zone.

The IMD scientists said winds in Delhi have been strong since Tuesday afternoon and will get more intense on Thursday. VK Soni, head of IMD’s environment monitoring and research centre, said the difference in maximum and minimum temperatures often lead to an increase in wind speeds over a region.

On Wednesday, the maximum temperature at the Safdarjung observatory, which is considered the official marker for the city, was 18.3 degrees Celsius, while the minimum was 7.8 degrees Celsius.

“The wind speeds are expected to be higher on Thursday and the air quality will improve further, but remain in the “poor” zone. On Friday, there air quality may deteriorate again, but it will be a temporary dip as there is a forecast of wind speeds going up again from January 23,” Soni said.

Kuldeep Srivastava, head of IMD’s regional weather forecasting centre, said the wind speed on Wednesday ranged between 15 and 16kmph and was blowing from the north-west. He said because of the strong winds, the “feels like” temperature, which is the temperature that a human body perceives, was also lower than the actual recording.

“In the morning hours, we had shallow to moderate fog. In the coming days, the temperature will be around 7-8 degrees Celsius, but there will be a fall from January 24. The minimum temperature is likely to fall to around 4 degree Celsius and the maximum temperature is also expected to fall by two to three degrees,” Srivastava said.

He said the fall will be the result of a western disturbance over the western Himalayas, which will lead to rainfall and snowfall in parts of Jammu and Kashmir and Himachal Pradesh on January 22 and January 23.

“After this western disturbance passes, the wind direction will change and the temperatures in Delhi and neighbouring areas will fall,” Srivastava said.

Minimum temperatures are likely to fall by 2-4 degrees over most parts of north-west India, over the next three days, leading to cold wave conditions.

“Cold day” or ”severe cold day” conditions are likely over west Rajasthan during next 24 hours and over Bihar during next three days, IMD said in its Tuesday bulletin.

According to IMD, a cold day or a severe cold day is classified as such based on two parameters—a minimum temperature of under 10 degrees Celsius and a maximum temperature of 4.5 degree Celsius or 6.4 degrees Celsius below normal, respectively.

A cold wave occurs in the plains when the minimum temperature is 10 degrees Celsius or below and/or is 4.5 notches lower than the season’s normal for two consecutive days. A cold wave is also declared when the minimum temperature is less than 4 degrees Celsius in the plains.