Residents across north interior Karnataka and Bengaluru were caught off guard last week as temperatures dipped sharply, making mornings and nights feel more like peak winter than the usual mild December weather. Between December 8 and 14, several regions recorded temperatures far below normal — but what caused this sudden chill?
According to weather experts, the cold spell was not the result of a single factor. Instead, it was caused by a rare combination of global weather patterns, long-distance wind movement, and local atmospheric conditions working together.
A Global Weather Pattern Set the Stage
To understand why Karnataka felt unusually cold, scientists say we need to look far beyond India — all the way to the Pacific Ocean. This winter is unfolding under La Niña conditions, a global climate phenomenon marked by cooler-than-normal ocean temperatures.
La Niña doesn’t just affect one region; it alters weather patterns across the globe. By strengthening trade winds and shifting atmospheric circulation, it often increases the chances of colder winters in parts of Asia, including India.
In simple terms, La Niña created the right background conditions for colder air to move southward.
Cold Air Travelled From Siberia
While La Niña prepared the atmosphere, the main source of the cold was the Siberian High — a massive zone of cold, dry air that forms over northern Asia every winter.
Normally, this icy air mass remains confined to its region, blocked by mountain ranges like the Himalayas. However, this December saw a unique pressure setup that allowed some of that cold air to break free and move south.
As a result, districts such as Vijayapura and Bidar recorded temperatures close to 7°C, nearly 8 degrees lower than normal. Even Bengaluru, which typically stays warmer due to urban heat, saw temperatures drop to around 12.9°C at the airport.
Clear Skies Made Nights Even Colder
But the cold winds alone don’t fully explain how severe the chill felt — especially at night.
Scientists point to a process called nocturnal radiative cooling. During this period, the atmosphere over Karnataka was extremely dry, with clear skies and very little moisture in the air.
Normally, clouds and water vapour act like a blanket, trapping heat near the ground. Without that protective layer, the earth’s surface lost heat rapidly after sunset — almost like leaving a window open on a cold night.
This led to dramatic temperature swings, with daytime warmth quickly giving way to sharp nighttime drops of 15°C or more.
Pleasant Days, Biting Nights
The result was a classic winter contrast: comfortable afternoons followed by freezing nights and early mornings. Bonfires became common sights in many areas as people tried to keep warm during dawn hours.
Experts say such conditions are uncommon but not impossible, especially when global and local weather factors align so precisely.
What Happens Next?
While temperatures are expected to gradually stabilise, scientists note that climate patterns like La Niña can continue to influence weather for weeks. Residents are advised to stay prepared for cooler-than-usual nights, especially in interior regions.
This cold spell serves as a reminder that even regions close to the Equator are not immune to the ripple effects of global climate systems.
