Delhi-NCR residents woke up on Makar Sankranti, January 14, 2026, expecting a familiar winter scene of lingering cold, routine fog and sluggish traffic. Instead, the capital witnessed an unusual and dramatic weather event that unfolded within minutes and vanished just as quickly.
Between 7:45 am and 8 am, a dense curtain of fog suddenly enveloped large parts of Delhi and its surrounding regions, reducing visibility to almost zero. Roads, flyovers and railway tracks disappeared under a thick white haze, leaving commuters stunned. What made the event striking was its brevity. Within a short span, the fog began to thin and dissolve, restoring visibility almost as suddenly as it had vanished.
This was not the typical overnight fog that blankets north India during winter. Meteorologists describe the episode as a case of rapid-onset fog, commonly referred to as flash fog, a rare phenomenon that forms and dissipates under highly specific atmospheric conditions.
Fog, in simple terms, is a cloud that forms at ground level when air near the surface cools enough for water vapour to condense into tiny droplets. In north India, this usually happens gradually overnight due to radiation cooling, leading to the familiar morning fog that lifts slowly with sunlight.
Flash fog, however, behaves very differently. In Delhi’s case, the atmosphere already contained high moisture levels from lingering overnight fog. As daylight began to break, a brief influx of colder air near the surface, triggered by subtle shifts in wind direction and weak air movement, prevented temperatures from rising as expected. Instead, temperatures dipped or stagnated abruptly, pushing the air to its dew point and causing immediate condensation.
The process is similar to breathing onto a cold mirror, where moisture condenses instantly. When this happens over a wide area already saturated with moisture, fog can form almost instantly and become extremely dense.
High humidity played a central role in the intensity of the fog. In urban environments like Delhi-NCR, pollution particles act as condensation nuclei, providing surfaces for water droplets to cling to. This interaction makes fog thicker and more opaque, causing visibility to drop to just a few metres within minutes.
Low wind speeds further worsened the situation. With little air movement to disperse the moisture, the fog settled quickly over roads, residential areas and open spaces, creating dangerous conditions for drivers and commuters.
The disappearance of the fog was just as swift. As sunlight strengthened, surface temperatures rose enough to disrupt the fragile balance that had allowed the fog to form. Even a slight increase in warmth, combined with marginal airflow, caused the suspended droplets to evaporate back into water vapour. The fog did not drift away; it simply ceased to exist.
Meteorologists warn that flash fog events are particularly hazardous because they occur with little to no warning. Unlike overnight fog, which can be forecast hours in advance, rapid-onset fog catches commuters, pilots and transport authorities off guard, increasing the risk of accidents.
With cold wave conditions continuing across north India, experts caution that similar short-lived but intense fog episodes could recur in the coming days. These sudden weather surprises may be brief, but their impact on visibility and safety can be severe.