Delhi NCR woke up to a thick blanket of fog this morning, with visibility dipping to as low as 600 metres in parts of the region during the early hours. The development surprised many, as both minimum and maximum temperatures have remained well above normal in recent days.
For the past few days, Delhi and adjoining areas have been witnessing unusual weather phenomena that have caught many residents off guard. Since the beginning of this month, maximum temperatures have consistently hovered above 35 degrees Celsius, marking one of the hottest early March periods in nearly 50 years.
The India Meteorological Department (IMD) attributed Tuesday's dense fog to a combination of meteorological factors. At present, a Western Disturbance is impacting the mountains of the western Himalayas. This has led to the formation of a stable boundary layer at lower levels.
The stability has been accompanied by easterly winds bringing higher moisture from the Bay of Bengal. The combination of these conditions trapped cool, moist air near the surface, resulting in fog formation despite the daytime heat.
IMD scientists said such events are not entirely unusual for early March in northwest India, including west Uttar Pradesh and adjoining Delhi-NCR, when similar atmospheric conditions prevail.
Breaking Down the Meteorological Factors
Fog typically forms when moist air cools to its dew point overnight and persists into the morning under calm winds and high humidity. On Tuesday morning, the Western Disturbance over the Himalayas blocked stronger winds, creating stability that prevented vertical mixing of air.
At the same time, easterly winds, unusual for this time of year, transported moisture from the Bay of Bengal, enhancing condensation even as daytime temperatures climbed due to clear skies and solar heating.
Daytime temperatures above 35 degrees Celsius are largely due to the absence of prolonged cloud cover, while nights cool relatively quickly during spring, creating favourable conditions for radiation fog.
Is It Really Abnormal For March?
Data suggests that fog spells in March have occurred in the region earlier under comparable conditions. One notable episode took place between March 6 and 8, 2008, when dense fog triggered multiple failures in critical electrical transmission lines across northern India, causing widespread power outages.
Similar incidents were reported in 2010 and 2013, when fog-induced insulator pollution and line faults led to grid disruptions.
IMD records show that early March fog in west Uttar Pradesh and Delhi-NCR is often linked to weak Western Disturbances. This year too, dense fog was observed around March 3-4 under similar atmospheric conditions.
