New Delhi: As heavy rainfall lashed the Capital on Monday, residents woke up to what they called a ‘night-like morning’, as dark clouds blanketed the whole city until 9 am, amid roaring thunder and lightning flashes.
While it is not the first time that such weather was observed over Delhi, meteorologists stated that an activity like this does occur during winter months. Similar weather was observed around January 24 last year, when skies in the city remained engulfed in dark clouds till 11:30 am, recall officials.
“The weather was not unusual. It was because of an active western disturbance located over north Pakistan and adjoining Jammu and Kashmir, which has brought heavy rain, thunderstorm and hailstorms to north-western states. However, the current system was intense and so a heavy rainfall alert was issued for the region," said senior scientist M Mohapatra, who is also Head Services, India Meteorological Department (IMD), New Delhi.
Western disturbances are basically extra-tropical storms which originate over the Mediterranean region and are noticed as cyclonic circulation/trough, or as a low pressure area on the surface. Loaded with moisture from Mediterranean Sea, Caspian Sea and Black Sea, these storms move eastwards towards Iran-Afghanistan, Pakistan and India, where the Himalayas obstruct them and cause rain and snowfall over the region.
In general, this system is mostly active along the western Himalayas, but occasionally the intensity is so high, that it reaches the north-western plains and brings heavy rainfall.
“The current system was very intense," said Sathi Devi, Head, National Weather Forecasting Centre, India Meteorological Department (IMD). “So, it could reach up till Delhi and brought rainfall and thunderstorm. Not all western disturbances impact the plains."
Out of around five western disturbances which usually hit the western Himalayas in a month, not more than three reach the plains and cause rainfall, highlight officials. This year, out of the three systems formed so far, only two caused rainfall in Delhi.
"The passage of western disturbances is a regular feature in the winter season from October to February, but January is the peak season for such weather systems," said Kuldeep Srivastava, Director, Regional Weather Forecasting Centre (RWFC) of IMD.
Weather scientists also contend that the movement of new upper air troughs could also be affecting the western disturbances, leading to heavy rainfall and thunderstorms. The current system also had high moisture feeding from Arabian Sea.
“In western disturbances, cyclonic circulation is formed at the lower and middle level of the troposphere and trough at the upper level. If a trough starts forming in the upper troposphere over the Mediterranean region and it leads to formation of a low pressure region over north-west India, causing an incursion of moisture from the Arabian Sea, then it can produce heavy rains," said Srivastava.
The government’s weather department had located the disturbance over North Pakistan and Jammu and Kashmir on January 21 and issued a warning of an intense spell of rain over north-west India, coupled with a possibility of thunderstorm and isolated hailstorm in the region from January 21 to January 25. A red-alert for widespread heavy rainfall was also issued for Jammu and Kashmir and Himachal Pradesh.
In its latest forecast, IMD has issued an alert for yet another western disturbance which is likely to hit the western Himalayas around January 25, however weather officials highlight it is not likely to be as strong as the current spell. But it will bring light rainfall and snowfall, mainly in Jammu and Kashmir, Uttarakhand and Himachal Pradesh.
Meanwhile, the night temperatures are also expected to fall by 2 to 4 °C after Tuesday and maximum temperatures would be in the range of 20 to 22 °C, as per the forecast.