Cold air, fog will persist over North India as Western Disturbances remain away.

January remained cold in North India. Cold or severe cold wave conditions are exacerbated by lingering fog as weather-generating western disturbances stay away. This is unusual for an El Nino phase, when active westerly disturbances are the norm rather than the exception, bringing snow to high elevations and rain/thunderstorms to the plains. This also goes against India Meteorological Department (IMD) forecasts and international weather models. For example, the IMD projected monthly rainfall to be above normal (and 122 percent of the long-term average, LPA). For the country as a whole, it was forecast to remain below normal (jagt; 118 percent LPA) over most of the country, except some pockets of Northeast India and Northwest India.

All India Rainfall Deficit

All India Deficit till January 23 was 56 percent, Deficit category included four Met subdivisions, 15 in the category of great deficit; while five received no rain at all. With only a week left for the end of January, the west coast and the adjacent southern peninsula received heavy to heavy rainfall, while the north-west, east and east-central parts of India were noticeably deficient. The rainfall deficit is due to the lack of westerly disturbances following the howling winds as part of the upper-level jet stream remains stationary over northern India, forcing seasonally cold arctic winds to descend. They held back not only the cold air, but also the seasonal fog in the huge hold, and refused to let go for almost a week. The IMD said on Wednesday that these conditions will dominate the country for another 4-5 days, including Republic Day.

Moisture Transport

Winter rain and snow are controlled by moisture transport in the upper atmosphere (jet stream) with induced circulation in the lower levels of the Arabian Sea. Moisture from the Arabian Sea is the main factor causing heavy rainfall near the Himalayas due to rapid vertical ascent and intense cloud formation due to the orographic (mountain effect). Moisture condenses quickly to form clouds, rain or snow, which are important to the region in winter. Induced circulation develops after active/intense western disturbances that rarely occurred during the winter. But they also require separate heating from the cold air to the north of the jet stream and the warm air to the south, which may have somehow played a role this year, although El Nino years usually cause western disturbances. Active disturbances sink into the subtropical jet stream over northern India, but not this year.

Excess Rain in South

While North India has been blank so far, the West Coast and South Peninsula have experienced excess/severe excess rain due to a western disturbance over the Bay of Bengal/Arabian Sea. Coastal Karnataka was the biggest beneficiary at +2,346 percent, followed by Konkan and Goa (+1,126 percent); and Lakshadweep (+992 percent). Kerala and Mahe managed +907 percent; South Interior Karnataka, +383 by crack; and Tamil Nadu, Puducherry and Karaikal, +363 percent..

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