On the morning of Makar Sankranti, January 14, 2026, Delhi-NCR was engulfed by a sudden, dense fog that reduced visibility to near zero within minutes, only to vanish almost as quickly as it appeared. This intense, short-lived event was a classic case of ‘flash fog’, a rapid-onset phenomenon that poses unique risks.
Key Takeaways
- Sudden Onset: Dense fog formed between 7:45 and 8 AM, catching the city off guard.
- Specific Conditions: Triggered by a mix of cold wave, high humidity, and sudden wind/temperature shifts.
- High Danger: Flash fog is a major safety hazard for transport due to its unpredictable nature.
- May Recur: Meteorologists warn such episodes could happen again this winter.
What is Flash Fog?
Fog is essentially a cloud at ground level, forming when air cools enough for water vapour to condense. While typical winter fog in North India forms slowly overnight (radiation fog), flash fog develops and dissipates rapidly under specific conditions.
Meteorologists explain the January 14 event was caused by a combination of ongoing cold wave conditions, high atmospheric moisture, and a sudden change. As the sun rose, a brief influx of colder air—likely from shifting light winds—caused ground-level temperatures to dip suddenly. This rapid cooling pushed the air to its dew point, triggering instant condensation, much like breath fogging a cold mirror.
Why Did It Get So Dense, So Fast?
The high humidity was a primary factor. When the air is already saturated, even a small temperature drop can produce dramatic results. In urban areas like Delhi-NCR, pollution particles act as condensation nuclei, providing more surfaces for water vapour to cling to, resulting in a thicker, denser fog.
Low wind speeds also contributed, allowing the fog to pool rapidly over roads and open spaces instead of being dispersed. The fog’s equally swift disappearance was due to strengthening sunlight. A slight rise in surface temperature, coupled with marginally increased air movement, caused the water droplets to evaporate. The fog didn’t drift away; it simply ceased to exist.
Why Flash Fog is a Serious Concern
Rapid-onset fog events are particularly dangerous. They catch commuters, drivers, and pilots completely off guard. Unlike predictable overnight fog, flash fog offers little to no warning time, making sudden visibility loss a critical safety risk.
With winter continuing and cold wave conditions persisting, meteorologists warn that such short, sharp, and disruptive fog episodes may recur. Understanding the science behind them is the first step in improving preparedness and public safety alerts.
