There’s many a twist in Delhi winter’s tail
The western disturbance that caused rain and chilly winds on Monday and Tuesday will likely continue till Thursday and another disturbance is expected on March 2 and 3, the India Meteorological Department (IMD) has said, highlighting the profusion of these extratropical storms that have hit north-west India this winter.
“Widespread rain, snow along with isolated thunderstorms and hailstorms are likely over Himachal Pradesh and Uttarakhand and scattered to fairly widespread rainfall with isolated hailstorms over Haryana, Chandigarh, Delhi and Uttar Pradesh during next 24 hours,” IMD’s bulletin on Wednesday stated.
The disturbance made Wednesday the coldest late February day in at least seven years, IMD said, with day-time temperature dropping to 20 degrees Celsius, at least six degrees below normal.
Strong surface winds speed reaching 30-40 kmph gusting to 50 kmph are also likely over plains of northwest India, over Haryana, Uttar Pradesh and north Madhya Pradesh till Thursday evening, IMD added.
The western disturbance on March 2 and 3, the 15th of the season, is likely to cause severe weather again in northwest India, but only on those two days.
IMD meteorologists said there may only be a marginal and temporary drop in temperature following it. “We are expecting rain and thunderstorms in the northern plains and snowfall in the hills on March 2 and 3. The temperature drop after the western disturbance passes will not be significant,” said M Mohapatra, director general of meteorology at IMD.
“This could be the last chill of the winter months, as according to meteorological terms December, January and February are considered the official winter months. From March, the wind pattern starts changing, paving way for the summer season. March is more of a transient month in which we experience both winter and summer type temperatures,” said B P Yadav, referring to Wednesday’s chill.
India usually sees five to six western disturbances in winter. Mohapatra explained the frequency and number of disturbances are high this year because of the weakening of the Polar Vortex. The disturbances develop due to a temperature difference between northern and southern latitudes. They are more intense this time because of the higher temperature gradient which is a result of the weakening of the Polar Vortex, he said.
Polar Vortex is a pocket of very cold air in the northern hemisphere which lies near the polar region in winter. Due to disturbances in its jet stream, cold air affects parts of US. For example, this year large parts of North America were gripped by an influx of Arctic air.
IMD data since 2012 shows that night temperature hovers between 13 and 15 degrees Celsius in the last week of February. It has never dropped below 10 degrees over the past six years. The maximum temperature ranges between 25 and 32 degrees Celsius during the last seven days of February.
This year, average night temperature since February 20 is 11.8 degrees Celsius and average day temperature, 23.2 degrees Celsius. The rain and strong winds helped settle dust and blow away local emissions, taking Delhi’s air quality index (AQI) to the “satisfactory” category, which is a rare occurrence. According to the Central Pollution Control Board data, the overall AQI in the city was 99.