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Cloud cover, hint of rain to keep Celsius in cool zone

Sunday was the coolest March 2 in five years as an overcast sky produced a sprinkling of rain that scientist call “traces of rainfall”.

The forecast for the next two days, according to the Met office, is “an outside chance of rain” because of a trough pulling moisture to the city from the Bay.

The blink-and-miss weekend rain and the accompanying clouds had a big cooling effect. The maximum temperature did not climb beyond 29.7 degrees Celsius, two notches below normal, with the sun playing peekaboo throughout Sunday.

The weather hasn’t been so kind in the past years. The city had sweltered at 37.1 degrees Celsius on March 2, 2010. (See chart)

According to the experts, the weather will remain pleasant on Monday. Rain is expected but the chill is unlikely to return.

“We expect rain in Jharkhand, Bihar and parts of Bengal on Monday. The wind and pressure patterns reveal an outside chance of rain in the city,” said an official of the India Meteorological Department, Calcutta.

The maximum temperature is expected to remain below the 30-degree mark in the next couple of days.

The minimum reading of 19.5 degrees Celsius on Sunday was below normal too, but only just. Not much fluctuation is expected in the nights till Tuesday.

“The cloud cover over Calcutta, because of a trough of low pressure in the upper levels of the atmosphere, stretches from Chhattisgarh to the western districts of Bengal. This is drawing moisture from the Bay of Bengal and producing clouds,” said an official of the IMD.

A trough with lower atmospheric pressure than its surroundings attracts air towards it. The one above the districts is pulling moisture-laden air from the Bay.

The maximum temperature in Calcutta has been on the lower side for the past week because of several conditions working towards cloud formation.

A high-pressure belt on the Bengal-Odisha coast had pushed moisture inland last Tuesday. As the week progressed, a cyclonic circulation over Jharkhand and adjoining areas supplemented the coastal system.

By Friday, thunderclouds covered almost the whole of eastern India because the confluence of hot and cold air in the Jharkhand-Chhattisgarh-Madhya Pradesh belt. Before this system dissipated, another trough of low pressure started brewing.

Meteorologists said the trough would weaken on Wednesday. That means no more clouds to protect the city from a scorching sun.