Don't further delay that visit to the dry-cleaners to dust up your blazers and coats. Winter is likely to set in a bit early this year.

The Met department has forecast that temperatures will dip in the coming days. Reason - there is a western disturbance as an upper air cyclonic circulation is hovering over north Pakistan and neighbouring areas.

A western disturbance is an extra tropical storm originating in the Mediterranean region that brings sudden winter accompanied by rain and fog to the Indian sub-continent.

"It is a non-monsoonal precipitation pattern driven by the westerlies," said a Patna Met department official.

Another reason for the sudden weather change is that the winds are currently blowing from the northwest direction, as against from southwest till a couple of days ago, causing intrusion of cold air, he added.

The mercury has been plunging in Patna since last week.

From around 36°C a week ago, the maximum temperature has already dipped to 32°C and is likely to dip further down, to around 30°C in the next two-three days, according to data provided by the India Meteorological Department (IMD).

Similar is the case with minimum temperatures.

The minimum temperature in Patna was around 26°C till a week back and has come down to 22°C.

It is further expected to come down two notches lower to 20°C by October 23.

With the southwest monsoon having completely withdrawn from Bihar, winter is gradually setting in.

Already, residents can feel a nip in the air in the early mornings and also late at night.

Though the exact date of onset of winter in the state has not been officially announced, weathermen claim it will cover the state fully after Chhath, around November 10.

It is officially called winter when the minimum temperature dips below 15°C.

In Patna, winter had set in on November 18 last year and around the first week of December in 2013 and 2014.

As of now, there is big variation in diurnal temperatures. "This is the transition period as we are approaching winter," said Patna meteorological centre director Soumendu Sengupta.

"The western disturbance, which affects day to day weather in northwest India, especially during winter, will continue for another few days."

Another factor behind cooling down of the temperature is the upper air cyclonic circulation over east central Bay of Bengal and its neighbourhood, extending up to 3.1km above mean sea level now, the India Meteorological Department website said on Tuesday.

Under its influence, a low-pressure area is likely to develop over the region during the next 24 hours, it said.

In a low-pressure system, air rises, cools down further and clouds begin to form.