Delhi has been experiencing below-normal temperatures for the last couple of weeks, thanks to weather phenomena such as western disturbances. But what exactly are western disturbances and how do they influence the weather in the Capital?
Minimum temperatures in March normally fluctuate between 12 and 18 degree Celsius, with the mercury rising as the month moves along.
However, temperatures dropped to 9.4 degrees Celsius on Holi, and further dropped to 9.1 degrees Celsius by Tuesday, a day after the festival. This was way below the expected normal minimum temperature for the time of the year, 15 degrees Celsius.
This is quite uncharacteristic as Delhi has not had temperatures lower than 10 degrees Celsius during March, since 2011, according to the India Meteorological Department records. The lowest temperature that was recorded in Delhi during March was in 1945, when the minimum temperature dropped to 4.4 degrees Celsius on March 6.
Weathermen have blamed western disturbances for the unexpectedly cold days in Delhi. Western disturbances are essentially ‘storms’ that originate in the Mediterranean. They create a pocket of wind and pressure differences, which also changes wind directions influencing temperature levels in northwestern parts of India.
“This year, the frequency of western disturbances have been very high. This would explain why the weather kept changing so often in Delhi,” explained a weather expert.
Delhi is usually warmer when the western disturbance is right to the west of India, and it gets cooler once the storm moves to over north and north western Himalayas and moves across India.
“Ahead of a western disturbance coming to India, temperatures tend to rise. This is because it pushes warm air in front of it. This is followed by a gush of cooler air, after it passes,” said an India Meteorological Department (IMD) official.
The winds that follow a western disturbance are usually stronger westerly winds, which are cooler as they pass over colder regions of the Himalayas before reaching the national capital.
Western disturbances are also held responsible for winter and pre-monsoon showers in Delhi and neighbouring parts, as they bring moisture-rich winds with it too. So a western disturbance moves in a cyclic manner, where it first raises the temperatures of the city, with slower warmer winds, this may give way to some rainfall, before it cools down again with stronger colder westerly winds.
Though western disturbances are common during winters, they can occur at other times too, which explains the sporadic weather over the last week.
Under the influence of a western disturbance, temperatures were docked above normal ranges before Holi, which was followed by some rainfall in the city. This then gave way to the chilly Holi day on Monday.
With another western disturbance currently brewing just to the west of India, the city is expected to witness similar weather patterns soon again. Temperatures settled at 14 degrees Celsius on Thursday morning, and is expected to rise as high 29 degrees Celsius during the course of the day.
The minimum temperature is expected to rise to 15 by Sunday, before dropping to 14 degrees Celsius again by Wednesday.
Weathermen at the IMD have predicted the possibility of rain and thunderstorm on Sunday.
However, this time after the western disturbance passes, the temperature is expected to keep rising.
“This is just seasonal change. This time of the year, as a precursor to monsoon, it usually gets warmer in the city,” explained the IMD official.
By Wednesday, the maximum and minimum temperatures are expected to be 33 and 14 degrees Celsius respectively.