Cold snap: Expect a long winter, says weather dept

Experts cite La Niña, IOD as reason for extended cold front.


Sumera Khan January 21, 2012

ISLAMABAD:


Pakistan is bracing for a long winter this year with weather experts predicting a colder than usual spell over the next few weeks – one that will extend till March. This winter is likely to be the coldest of the last two decades, according to the Pakistan Meteorological Department’s (MET) experts.


“Since the beginning of December 2011, Pakistan is in the grip of a cold wave,” said Dr Ghulam Rasool, chief meteorologist who heads the department of research and development in Islamabad.

Rasool told The Express Tribune that colder than normal temperatures were useful for wheat as vegetative growth of the plants retarded, and the tilling process started increasing the number of tillers per plant. On the other hand, potato and young vegetable crops suffered serious damage due to continued frost during December and January. Three spells of snowfall gathered lot of snow over the Himalayas, Hindukush and Karakoram.

December was a cold and dry month, sending chill winds down to the coastal areas including Karachi, while January brought some rains to Barani (rain-fed) areas of Khyber-Pakhtunkhwa and upper Punjab, which provided relief to the Rabi crops, particularly wheat, which was attacked by termites in some areas due to the extended dry spell.

While describing the reasons behind the second anomaly of the year 2012, Rasool said that the persistent cold wave over Pakistan and other Asian countries is the combined effect of La Niña and the Indian Ocean Dipole (IOD), oceanic processes in the Pacific and Indian Ocean, respectively.

He added that La Niña conditions occur when eastern equatorial Pacific water becomes colder than normal. It is the reverse of El Niño, and sends such a strong signal that this single event can shatter the weather pattern all over the globe. Now the Pacific water in that region is 1C colder than normal. IOD is a seesaw like temperature pattern of the eastern and western Indian Ocean with a respective warmer and colder zone. IOD is now in negative phase. He said both the factors favoured to draw the cold air of higher latitudes to the tropical and sub-tropical Asia. This pattern is expected to persist for a couple of months and make this winter a bit longer and considerably colder than normal.

Weather conditions ahead

On average, three to four westerly waves per month are expected to pass across the northern latitudes of the country till the end of March. They are likely to produce substantial snowfall over the mountains providing good frozen water reserves to maintain river flows in the typically dry months of May and June by way of melted water. Westerly waves may bring good amount of rainfall over the agricultural plains of the country. Expected cold and wet spells in February and early March will provide favourable conditions for growth and development of wheat crops. Due to abundant moisture in the air, dense foggy conditions would hamper road transport and other activities during February also.

January

According to model predictions, precipitation in January was below normal by about 25-30%. Mainly dry weather continued over low elevation plains.

February

A few good rains are expected in the second half of February which would neutralize the drier first half. In this way February is expected to receive a normal amount of precipitation.

March

Due to increased convection, localized precipitation events will occur producing about 15-20% above normal precipitation during March.

Published in The Express Tribune, January 21st, 2012.

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