There is nip in the air, but the winter has not officially arrived in the city.

The minimum temperature has hovered between slightly above 13°C and 15°C in the past fortnight, giving people the chill feel. But according to meteorology, winter officially sets in at a place only after the minimum temperature remains below 13°C for at least a week.

Met officials have claimed that the temperature would start dropping from the next week. Thus, the official onset of winter is expected in the first week of December.

The north-westerly winds — the prerequisite for the drop in the mercury column in the winter — is blowing in the city but concurrent low pressure over the Bay of Bengal is keeping the winter season at bay. Weathermen have claimed that the low-pressure area over the Bay of Bengal is causing continuous incursion of moisture in the lower level of the atmosphere in the state, restricting the drop in the temperature.

The mean minimum November temperature in Patna is 14.9°C.

The lowest temperature at a place is usually recorded shortly before the sunrise. The presence of moisture in the lower level of the atmosphere at this time of the year retains the solar heat reaching the earth’s surface in the daytime, restricting the drop in the temperature at night and early morning.

Ashish Sen, the director of India Meteorological Department, Patna, claimed that the winter conditions were prevailing in the city but it had not set in officially.

“The prevailing north-westerly winds have brought the nip in the air but frequent depressions over the Bay of Bengal are not allowing the minimum temperature to drop drastically. A cyclonic circulation and a depression have formed in the Bay of Bengal over the past fortnight and two more depressions are expected within four days. All such weather systems are causing heavy moisture incursion in the troposphere, the lower level of the atmosphere, restricting the drop in the mercury column,” Sen told The Telegraph on Tuesday.

He added: “The two weather systems over the Bay of Bengal are expected to neutralise by November 23. The minimum temperature is expected to remain below 13°C thereafter.”

As the winter knocks on the doors of Patna, people have started feeling the chill. “I am making my four-year-old daughter wear four layers of clothes as she leaves for school at 6 in the morning. She wears an inner, a half- sweater, a shirt and a full sweater on top of them. I can feel the chill inside home, so I make sure that she is completely covered when she goes out,” said Arpita, a resident of Ashiana Nagar.

Not just the children, people of all age groups have taken out their woollens. They are wearing them in the morning and evening hours.

The nip in the air has prompted rise in the cases of cold-related ailments. “These days are dangerous because the body is still not accustomed to the falling temperature conditions. People suffering from hypertension, heart diseases and diabetes should be cautious at this time of the year,” said Dr Rajeev Ranjan Prasad, faculty member, physiology, Patna Medical College and Hospital.

Flight withdrawn

Air India has withdrawn its afternoon flight AI-407/408 under its winter schedule, to be effective between December 1 and February 15, 2014. It has also rescheduled its morning flight AI 409. It will arrive at the Patna airport at 10.20am instead of 8.50am.