New Delhi, Jan 19 (PTI) The minimum temperature in the national capital settled at 7.4 degrees Celsius Wednesday morning with several parts of the city reporting shallow fog.Foggy and cloudy weather may lead to cold day conditions in several areas of Delhi, an IMD official said.Parts of the city have been reeling under "cold day" conditions since Thursday. The Safdarjung Observatory, considered the official marker for the city, also recorded a cold day on January 14 and January 15.According to the IMD, a "cold day" is when the minimum temperature is less than 10 degrees Celsius and the maximum is at least 4.5 degrees Celsius below normal.  A "severe" cold day is when the maximum temperature is at least 6.5 notches below normal.The IMD said minimum temperatures are likely to rise by two to four degrees Celsius in Northwest India during the next five days, under the influence of a fresh western disturbance (WD).   Widespread rainfall is likely over Punjab, Haryana, Delhi, west Uttar Pradesh and north Rajasthan from January 21 to January 23 due to the WD, it said.  The air quality index (AQI) of Delhi was recorded in the "very poor" category (330), data from the Central Pollution Control Board showed. An AQI between zero and 50 is considered good, 51 and 100 satisfactory, 101 and 200 moderate, 201 and 300 poor, 301 and 400 very poor, and 401 and 500 severe. PTI GVS  SRY