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Dense fog has hit Delhi several times over the past 10 days, in what meteorologists are calling a “unique” event. Dense fog events are not common in the second and third week of February, as temperatures start rising.
IMD officials said moist easterly winds, low wind speed, lack of western disturbances, and an easterly system over central India are responsible for the weather event, which has affected Delhi, Punjab and Haryana.
On Friday, flight departures were stopped between 7.15 am and 8.30 am and around 70 flights were delayed. As airlines have many pilots trained to land in very low visibility conditions, only departures were affected, not arrivals, airport officials said.
In the last 10 days, at least 15 flights have been affected each day due to low visibility levels, the official said. “Unusual and very dense fog coverage over the Delhi-Haryana-Punjab and Lahore-Amritsar-Hisar-Delhi belts has been seen persistently at the airport as well as in satellite data. It is an unusual spell in terms of its duration. It lasted over Punjab, especially at Amritsar, airport from 7-8 pm till around 10.30 am the next morning. In Delhi, it has caused very dense fog on 3-4 mornings. Never has there been such dense fog over large areas simultaneously for long durations daily for so many days, after February 10 in any winter. Dense fog in February is normal, but only in the first week. This year, this spell has occurred when night temperatures were 2 to 3 degrees Celsius above normal. This is unique,” said RK Jenamani, DGM, National Weather Forecasting Centre.
According to officials, while very dense fog (visibility dropping to zero) was seen in December for only 1.5 to 2 hours, in February, there have already been 5 hours with very dense fog.
Among the main reasons for this trend, Jenamani said, was the absence of an active western disturbance affecting the plains: “This caused an anti-cyclone high pressure belt. Anti-cyclone causes stable boundary layer and inversion and calm winds at lower levels — the number one criteria for dense fog to persist.”
High pollution levels — Delhi’s air quality on Friday was very poor with the AQI at 311 — also contribute to fog formation.
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Easterly wind patterns over central India have also contributed to bringing more moisture in Delhi’s air. Usually at this time of the year, dry wind blows in from the west or northwest region. Moisture is a prerequisite for fog. On Thursday and Friday, the highest humidity recorded was 100% (during morning hours).
IMD has forecast moderate to dense fog on Saturday, and moderate fog on Sunday and Monday.
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