Over NW India, air quality decreases; the temperature should remain below average.

Key sentence: 

1. Winds are expected to slow down, and ventilation is likely to decrease significantly from 14 to January 18.
2. Minimum temperatures were likely to stay below average for most northwestern India parts over the next 3-4 days.
3. Several towns and cities across northwestern India began to report very poorly to extreme air quality on Thursday.

ventilation is likely to reduce from January 14 to 18:

Under the Ministry of Earth Sciences’ air quality warning system for Delhi, winds are expected to slow down, and ventilation is likely to decrease significantly from 14 to January 18, leading to a further deterioration in air quality.

Air quality is expected to deteriorate and hit the upper end on Thursday of the very poor category and Friday of the extreme category.

An Air quality index of 389: 

With such an air quality index of 389 today, Delhi registered very poor air, though Ghaziabad, Faridabad, and Greater Noida are in the extreme group.

Minimum temperatures were likely to stay below average for most northwestern India parts over the next 3-4 days due to dry north/northwestern winds blowing over the area.

Severe cold day conditions are likely to continue in such places: 

Cold day/severe cold day situations over Punjab and Haryana Chandigarh, Delhi, and even in some pockets of Uttar Pradesh including Uttarakhand over the next three days are likely to persist in many pockets.

Cold wave/severe cold wave situations over Punjab, Haryana, Chandigarh, Delhi, and Uttar Pradesh are likely in several pockets; over East Rajasthan in certain pockets West Rajasthan in isolated pockets within the next 3-4 days.

Land frost over Uttarakhand, Chandigarh, West Uttar Pradesh, Punjab, Haryana, and north Rajasthan is also quite likely to occur in isolated pockets next two days.

According to India Meteorological Department: 

A cold day or extreme cold day is defined as such based on two criteria, as per the India Meteorological Department: a minimum temperature below 10 degrees and a maximum temperature of 4.5 degrees C or 6.4 degrees C below average, accordingly.

In the plains, a cold snap occurs whenever the minimum temperature is 10 degrees Celsius or under and for two consecutive days, 4.5 notches lower than the regular season. Often, a cold wave is announced when the plains’ minimum temperature is far less than 4 degrees C.