Delhi saw an unusual episode of shallow fog on Thursday morning much to the bemusement of its residents used to searing May days. At 15.8 degrees Celsius, it was the third coldest May morning since 1901.

May has historically been the hottest month of the year in the city with a mean maximum temperature of 39.5 degrees Celsius.

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.

"Fog on a May morning in Delhi. Never ever before have I experienced this in over 4 decades of living in this city. This is surreal!" a Twitter user said.

"Fog in Delhi on a summer morning! Same time last year, we were in a heat wave!" another person said.

Weather department officials said high moisture content in the air, calm winds and a significant difference between the daytime and nighttime temperatures create conditions that are favourable for the formation of fog.

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

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.

The Safdarjung Observatory recorded the maximum temperature at least 10 degrees below normal on Sunday, Monday, and Tuesday due to intermittent rainfall and cloudy weather under the influence of successive western disturbances.

The maximum temperature settled at 28.7 degrees Celsius on Sunday and dropped to 26.2 degrees Celsius on Monday, making it the coolest first day of May ever since the weather keeping started in the country. The city recorded a maximum of 28.3 degrees Celsius on Tuesday.

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.

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