Why this winter has been colder, wetter, and largely fogless
- For many people, especially in North India, the winter of 2021-22 is appearing to be unusually cold and unusually long.
- The days, in particular, have felt colder and chillier than normal.
- Since December 2021, maximum temperatures across the North, Northwest and Central India regions have persistently remained below normal, resulting in “cold day” conditions.
- Technically, this means more than just a day that is cold.
- The India Meteorological Department (IMD) defines a “cold day” as one in which the maximum temperature falls below 16 degrees Celsius.
- This winter, the national capital Delhi witnessed eight days in January (until January 25) when the maximum temperature remained below 16 degrees, with the lowest maximum temperature recorded at 12.2 degrees Celsius on Tuesday (January 25).
- Similarly cold Januaries in recent years were felt in 2003, which saw 19 “cold days” in January, 2015 (11 days), and 2010, 2013, and 2004 (9 days each). There are several days still to go in January 2022.
Weather systems active over the country
- Winters over India are directly affected by the intensity and frequency of western disturbances — eastward propagating wind streams as a cyclonic circulation or trough, capable of inducing rain or snow-bearing weather systems along their path of movement.
- Until January 25, seven western disturbances had passed over India — nearly all of them strong enough to cause widespread rain, snowfall, and squally weather across large geographical areas between Pakistan and Northeast India.
- These systems caused hailstorms in northern Maharashtra, and heavy rainfall in Tamil Nadu.
- After a western disturbance crosses India, cold winds from the far north of the country penetrate to lower latitudes, and can reach up to even Telangana and Maharashtra, leading to colder weather, and sometimes to cold wave conditions.
- Back-to-back western disturbances separated by 10 days earlier this month caused a prolonged cold spell in Jammu and Kashmir, Punjab, Haryana, Rajasthan, Himachal Pradesh, Uttar Pradesh, Delhi, and Bihar between January 11 and 20.
- Precipitation, mostly in the form of snow, is common during winter over Jammu and Kashmir, Ladakh, Uttarakhand, and Himachal Pradesh.
- Light to moderate intensity rainfall is also commonly seen during winters in neighbouring regions of North India.
- This January, however, has seen widespread rain across the central, northwestern, northern, eastern, and northeastearn regions of India.
- As many as 24 states or Union Territories have recorded rainfall varying from excess to large excess this month.
- January has been significantly wet over Delhi, Odisha, Madhya Pradesh, Uttar Pradesh, Uttarakhand, Haryana, Punjab, Chhattisgarh, Himachal Pradesh, Jammu and Kashmir, Ladakh, and Rajasthan, taking the all-India rainfall figure to 38.1 mm so far, which is 196 per cent above normal.
Foggy than normal
- December and January are known for the formation of dense fog across North India.
- Delhi in December normally witnesses 278 hours of fog — during which visibility falls below 1,000 metres — over 26 days, but December 2021 saw only 75 hours of fog spread over 22 days.
- This was the lowest for December since 1982.
- In January too, the national capital remained affected by fog for 252 hours against a normal of 292 hours — the lowest since 2008.
- IMD officials said the ongoing winter has recorded the lowest fog hours since 1991-92 over Delhi.
- Conditions for the development of fog are not forecast for the rest of January.