Dense February fog leaves weather experts surprised

In February, very dense fog has already been recorded for 3-4 hours. On Friday too, visibility at the Palam weather station fell below 50 metres. Other parts of the city also witnessed moderate fog.

Delhi over the last one week has witnessed a “never seen before” weather phenomenon for this time of the year. The temperatures have remained higher than normal, but the morning and evening hours have witnessed dense fog.

IMD categorises fog into four categories based on visibility-shallow (visibility up to 500 metres), moderate (up to 200m), dense (up to 50m) and very dense (zero visibility). (Representative Image) (HT photo/Raj K Raj)

IMD categorises fog into four categories based on visibility-shallow (visibility up to 500 metres), moderate (up to 200m), dense (up to 50m) and very dense (zero visibility).

India Meteorological Department (IMD) scientists said that Delhi has been witnessing dense fog since Monday, when visibility had fallen to less than 50 metres for some hours. Delhi, however, was not alone to be covered in this thick layer of fog. According to MeT officials, this fog cover has persisted during morning and evening hours above the entire Delhi-Haryana-Punjab region since February 11.

Scientists said that such dense fog over this region in the latter part of February was “never seen before”. IMD recordings show that till February 19, Delhi’s Indira Gandhi International Airport had already witnessed dense fog conditions for 13 hours, as against the average of 12 hours that is usually witnessed for the entire month.

Data also shows that in December last year, Delhi had experienced only one hour of very dense fog when visibility had hit zero.

In February, very dense fog has already been recorded for 3-4 hours. On Friday too, visibility at the Palam weather station fell below 50 metres. Other parts of the city also witnessed moderate fog.

RK Jenamani, senior scientist at the National Weather Forecasting Centre, said that such a long spell of dense fog has not been witnessed at such a large region at this time of the year ever before.

“This pattern of fog over Delhi and neighbouring states is unusual and has never been seen before. We have recorded dense fog over Delhi in February before, but that is only for two or three days, and that too in the first week of February. This time, the fog spell has occurred even when the night time temperature was 2-3 degrees above normal and that is unique,” said Jenamani.

He added that this weather phenomenon has also led to the visibility falling to zero in parts of Punjab as early as 7-8pm.

Weather recordings show that Delhi has been experiencing higher than normal maximum and minimum temperatures this month. Kuldeep Srivastava, head of IMD’s regional weather forecasting centre, said that except for four days, Delhi this February has recorded temperatures 3-4 degrees above normal.

“The maximum and the minimum temperatures have seen a spike this time and this is primarily because of clear skies and the absence of an active western disturbance over the plains for a prolonged period. Because there is no cloud cover, sunlight is hitting the ground with no interruptions,” Srivastava said.

On Friday, the maximum temperature recorded at the Safdarjung observatory, was 26.8 degrees Celsius, two degrees below the season’s normal. The minimum temperature was 9.9 degrees Celsius.

He also said that high pollution in Delhi is also contributing to low visibility.

“The low wind speed is not letting the pollution particles disperse and that coupled with the fog is also hampering visibility,” Srivastava said.

Central Pollution Control Board (CPCB) data shows that on Friday, the overall air quality index (AQI) of Delhi was 311, in the ‘very poor’ zone.

Scientists also explained that the last active western disturbance over Delhi was on February 4, and such a prolonged absence, can also be a reason behind foggy mornings and evenings. Another reason behind high temperatures and fog conditions is low wind speed and easterly winds coming into Delhi from Madhya Pradesh.

Easterly winds tend to be high in moisture content, and this has kept the levels of humidity high in Delhi. High moisture and low wind speed are basically the perfect combination for fog formation.

IMD forecast also showed that February this year is expected to break records of higher than usual temperatures and could also be the month when most number of dense fog days are recorded.

“There are no western disturbances forecasted, which means that foggy mornings and higher temperatures are expected to continue,” Srivastava said.