The hills and adjoining immediate plains of North-West India could look to some brief respite from the biting cold as a weather-altering western disturbance ambles in from across the international border.

Western disturbances carry moisture generated from the differential heating of the latitudes they traverse during winter; set up clouds which trap solar heat from escaping the atmosphere; and help maintain the surface warmth to the extent possible.

This is the type of respite that can do a world of good to most of the affected parts of North-West India, Central India and West India — thanks to severe cold conditions being kept at bay, though briefly.

Feeble disturbances

Attributing the severe cold to the lack of western disturbance activity, the India Met Department (IMD) said on Friday that three such disturbances moving across the Himalayan region last week were feeble ones.

They lacked moisture to precipitate as rain or snow; instead whatever moisture they had, got converted into fog or dense fog as they moved across the cold terrain of the region.

Rain and snow are generated when the disturbances venture deeper into the South as to scoop incremental moisture from the North Arabian Sea off Gujarat-Konkan and set up induced cyclonic circulations.

According to the IMD, the easterly wave activity across the Bay of Bengal in the South was confined to the Equatorial belt (Sri Lanka and further South). These waves can at times interact with western disturbances and set up interactive rain.

This also did not happen. The net result was that the cold wave conditions over North-West India became severe as the last week progressed. Colder Arctic westerlies to northwesterlies filled the plains to accentuate the winter climes.

Deficit N-E monsoon

The sole exception was the heavy rain lashing isolated places Andaman & Nicobar Islands on the December 20 and over Kerala on December 25. They seemed to have been the only beneficiaries of easterly wave activity.

The IMD assessed that rainfall during the week was 83 per cent below the long-period average for the country as a whole. North-West India and Central India drew a blank (deficit of 100 per cent) East and North-East India fared barely better with 95 per cent.

South Peninsula alone was in the ‘green’ with a deviation of +4 per cent, thanks to excess rain over Andaman & Nicobar Islands, Kerala and adjoining Coastal Karnataka, and Lakshadweep.

The North-East monsoon season so far (October 1 to December 26) has delivered a deficit of 43 per cent for the country as a whole. Central India and East and North-East India returned the worst individual deficit figures of 51 per cent each.

For North-West India, the deficit for the season so far was 39 per cent and for the South Peninsula, 36 per cent. Forecast for the next two weeks (December 28-January 3 and January 4-10) hinted at hit-or-miss showers for parts of Kerala and Tamil Nadu.

comment COMMENT NOW