Mercury to cross 42 degrees today in Delhi , yellow alert issued: What this means

Delhi weather update: The temperature in Delhi is expected to breach the 42-degree mark on Wednesday and cross 44 degrees Celsius by Thursday. Here's what a ‘yellow alert’ means.

Delhi is predicted to face an extreme heatwave in the next two days, the weather department has said, sounding a yellow alert warning for the residents of the national capital. The maximum temperature may even leap to 46 degrees Celsius in parts of Delhi, an official told PTI.

A heatwave is declared when the maximum temperature hits 45 degrees Celsius or is above 40 degrees Celsius in summer with a variation of five degrees or more above the normal temperatures. (File photo)

The temperature in Delhi is expected to breach the 42-degree mark on Wednesday and cross 44 degrees Celsius by Thursday as per the India Meteorological Department (IMD). “The heatwave conditions are likely to prevail in isolated pockets in Delhi till Thursday,” the Met Department said in a tweet. “Dust Storm and gusty winds” over Delhi, along with the adjoining states of Punjab, Haryana, and Uttar Pradesh have also been predicted for April 29.

The Safdarjung Observatory in Delhi reported a maximum temperature of 40.8 degrees Celsius on Tuesday as per news agency PTI. The all-time high maximum temperature for the month of April in Delhi was 45.6 degrees Celsius in 1941.

The alert system of the weather department in India

The India Meteorological Department (IMD) uses four colour codes for weather warnings:

Green - meaning no action needed

Yellow - suggesting vigilance

Orange - meaning residents must be prepared

Red - calling for immediate action

While the general view around the colour codes stays as mentioned above, IMD issues more specific guidelines to the public and authorities depending on the type of weather condition- rainfall, snowfall, thunderstorm, lightning, dust storm, heatwave, etc.

Declaring a heatwave

For the plains - as in the case of Delhi - a heatwave is declared when the maximum temperature is over 40 degrees Celsius and at least 4.5 notches above normal. A severe heatwave is declared if the departure from normal temperature is more than 6.4 notches, according to the IMD.

(With inputs from PTI)