The winter of 2021-2022 in North India has been noticeably colder and prolonged. Daytime temperatures have been significantly lower than the average, causing a chillier feel. This shift in climate is more than simply cold weather; it’s a result of various factors including Western Disturbances and La Nina.
Assessing the Weather Patterns
Since December 2021, the maximum temperatures across North, Northwest, and Central India have remained below average, resulting in “cold day” conditions. A “cold day” refers to times when the maximum temperature drops below 16 degrees Celsius, which is a familiar occurrence during the winter months in India’s northern plains.
Apart from the low temperatures, light to moderate rainfall is also fairly common during the winters in regions neighboring North India. However, January 2022 saw extensive rain across central, northwestern, northern, eastern, and northeastern parts of India. A remarkable 24 states or Union Territories reported varying degrees of excess rainfall this month.
Dense fog is another characteristic of North India’s December and January weather. However, January 2022 saw a decrease in fog hours in Delhi, reaching a low unseen since 1991-92.
The Causes: Western Disturbances and La Niña
Several factors contributed to this year’s unusually cold winter. By January 25, 2022, seven western disturbances had passed over India. These strong systems caused widespread rain, snowfall, and turbulent weather across large areas spanning from Pakistan to Northeast India. They triggered hailstorms in northern Maharashtra and heavy rainfall in Tamil Nadu.
Western disturbances are more frequent and numerous during La Niña. Currently, moderate intensity La Niña conditions are prevailing, characterized by cooler than average sea surface temperatures in the equatorial Pacific Ocean.
Following the passage of a western disturbance, cold winds from India’s far north penetrate lower latitudes, reaching as far as Telangana and Maharashtra. This leads to colder weather and occasionally to cold wave conditions.
The availability of low-lying clouds and moisture along the Indo-Gangetic plains also contributed to the cold day conditions and the additional chill factor experienced during daytime. This has been the longest and most intense spell of the season so far.
Understanding Western Disturbance
A Western Disturbance (WD) is an extra-tropical storm originating in the Mediterranean that triggers sudden showers, snow, and fog in northwest India. The disturbance moves from the “western” to the eastern direction, carried by high-altitude westerly jet streams. A disturbance refers to an area with reduced air pressure, and which strives to normalize its pressure.
La Niña Phenomenon
La Niña represents periods of below-average sea surface temperatures across the east-central Equatorial Pacific. It is indicated when the sea-surface temperature decreases by more than 0.9℉ for at least five consecutive three-month seasons. In India, La Niña typically results in cooler than average winters and above-average rainfall.