As temperatures continue to waver in unexpected directions, Delhi saw an unusual episode of shallow fog on Thursday morning, with mercury falling to 15.8 degrees Celsius, the coldest May morning since 1901.

May, which is historically the hottest month of the year in the national capital, usually recalls the maximum temperature of 39.5 degrees Celsius.

The Safdarjung Observatory recorded the maximum temperature at least 10 degrees below normal on Sunday, Monday, and Tuesday in Delhi.

This was due to intermittent rainfall and cloudy weather under the influence of successive western disturbances.

On Monday, the maximum temperature dropped to 26.2 degrees Celsius, making it the coolest first day of May ever since the weather keeping started in the country.

Delhi recorded a maximum of 28.3 degrees Celsius on Tuesday.

Why did Delhi see fog in May?

According to weather department officials, high moisture content in the air, calm winds and a significant difference between the day and night temperatures create conditions that form fog, according to news agency PTI.

According to the IMD, shallow fog is when visibility is between 501 and 1,000 metres.

Delhi is experiencing an unexpected pattern with cloudy skies, sporadic rain, and cool weather, which officials attribute to back-to-back western disturbances affecting northwest India.

Residents posted videos and pictures of fog blanketing the city’s skyline on social media.

The Safdarjung Observatory, Delhi’s primary weather station, recorded 30 mm of rainfall in 24 hours ending at 8.30 am on Thursday.

It logged a maximum temperature of 30.6 degrees Celsius, nine notches below normal, on Wednesday and a minimum temperature of 15.8 degrees Celsius on Thursday, the third lowest in the month since the weather keeping started in 1901.

The all-time low of 15.1 degrees Celsius was recorded on May 2, 1969. The city recorded a minimum temperature of 15.2 degrees Celsius on May 2, 1982.

Humidity levels oscillated between 80 per cent and 100 per cent at most places in the city.

Another spell of rain is likely Friday onwards, weather officials said.

Delhi recorded more than 20 mm of rainfall in April, the highest in the month since 2017, due to back-to-back western disturbances.

Another western disturbance is likely to affect northwest India starting May 5. Under its influence, cloudy skies and sporadic rain is predicted in the capital until May 7, an IMD official said.

The maximum temperature is predicted to remain below 35 degrees Celsius until May 8.

The Met office has predicted below-normal maximum temperatures and fewer heatwave days in northwest India in May.