The fact that no significant weather system is affecting the country for the time being has allowed dry and cold air to filter into the plains of Northwest, Central and even Peninsular India.
An update by the Noida-based National Centre for Medium-Range Weather Forecasting (NCMRWF) said that a feeble western disturbance sat over the northern parts of the country on Sunday.
FOG LIKELY
The system will get a move away to the east by Monday, and may set up fog to shallow fog conditions over the plains of Northwest India mainly during the morning hours.
Another western disturbance is likely to affect the northern parts of the country from later in the week, around Thursday, the NCMRWF said. The European Centre for Medium-Range Weather Forecasts (ECMWF) was in agreement with this.
Meanwhile, an India Meteorological Department (IMD) update on Sunday said that minimum temperatures have fallen by 2- 4 deg Celsius over East Uttar Pradesh, Bihar, Meghalaya, Manipur, Tripura, Madhya Pradesh, Vidarbha, Telangana and North Interior Karnataka.
POLAR AIR
These are places where colder polar northwesterly winds have been blowing from across the Northwest border.
The rest of West and Central India have continental westerlies as prevailing winds, steered around the West Madhya Pradesh-Mumbai area and into the Arabian Sea, bringing down the minimum temperatures in the process.
A seasonal IMD outlook had earlier said that moisture incursion, persistent clouding and rainfall had dented maximum temperatures and ratcheted up minimum temperatures over Northwest and adjoining Central India.
The setting in of northerlies/northwesterlies in the lower levels over the northern plains, which are generally responsible for advection of cold and dry continental air from the North, was also delayed in this manner.
COLD SNAP
But the mean temperatures for December are expected to remain slightly below normal.
The experimental extended range forecasts of IMD for the month also indicate higher (60-90 per cent) probability of below normal maximum and minimum temperatures over the plains.
Other global centres have also predicted high probability of below normal temperatures during this winter, the IMD said.
In this context, it cited the probabilistic forecast by ECMWF, which indicated a high probability of below normal temperatures during the three months period of December 2010 to February 2011.
LA NINA OUTLOOK
The Climate Prediction Centre (CPC) of the US National Weather Services quoted some international models as saying that prevailing La Nina conditions in the East Pacific could persist into the summer of 2011.
Historically, there are more multi-year La Nina episodes than El Nino episodes, but other than support from a few model runs, there is no consensus for a multi-year La Nina at this time, it said.
Consequently, La Nina is anticipated to continue into the Northern Hemisphere spring, with no particular outcome favoured thereafter.
The Regional Institute for Global Climate in Tokyo is already on record with a prediction for La Nina to extend into early 2012.
Back home, an IMD forecast for Northwest, West, Central and East India said that mainly dry weather would prevail over these regions until Wednesday.
MERCURY DIP
A gradual fall in minimum temperatures is to be expected over northwest, central and adjoining east India during the following three days from colder northwesterly winds. Continental westerlies may reduce the chill effect for West India.
As for South India, the last 24 hours ending Sunday morning saw scattered rainfall over Kerala, Lakshadweep, Assam, Arunachal Pradesh and Andaman and Nicobar Islands.
An Insat cloud imagery on Sunday showed the presence of convective (rain-bearing) clouds over parts of Southeast Bay of Bengal and the Andaman Sea.
The scattered rain and thundershower activity may continue over Kerala, Coastal and South Karnataka, Tamil Nadu and Lakshadweep for the rest of the week as westerlies blow in across the Arabian Sea.
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