A thunderstorm arrives like a troupe of monkeys on a tin roof. Or it sounds like a train thundering through your house. But it lasts only a bit. That’s enough, for the remainder of the day won’t be the same.

Now, you can use whatever you have at hand—a newspaper, plastic bag, book, kerchief, whatever—as armour against the fat raindrops from hitting your skull and face; you also can spit your curses up in the air over the ruined shirt, missed appointment, washed-off make-up and tousled mass of wet hair.

Or, you can regard the thunderstorm like a meteorologist. If you think about it, you cannot deny that this meteorological mass of air columns provide a brief respite from the heat when they open up.

Summer weather breeds thunderstorms. As temperatures shoot through the roof, more and more moisture accumulates in the atmosphere, and that moisture masses up and builds clouds. It especially builds thunder-and-lightning-making cumulonimbus clouds.

Every storm has the same fundamental ingredients: moisture, atmospheric instability and the trigger that keeps the interaction between the two going.  

Thunderstorms develop when the sun heats the ground, warming the air above it. This warm air rises in columns, creating an unstable situation as it meets cooler air above. For the instability to grow, a constant supply of warm air is needed from below, which can be pushed up by mountains or other barriers. As the warm air clashes with the cooler air, clouds grow larger, and moisture condenses into ice crystals.

These crystals collide, generating electrical charges that discharge as lightning. The rapid heating of the air from lightning causes it to expand violently, creating thunder. Most lightning occurs between clouds, with only a small percentage striking the ground.

Raghu Nadimpalli explains that thunderstorms are short-lived convective systems, mostly triggered by local dynamics rather than large scale changes. Raghu is a scientist with IMD, specialising in numerical weather prediction and forecasting.

Thunderstorms are associated with lightning, thunder, winds, and heavy rain. Sometimes they come with what are called squall winds, gusting up to 40 km per hour, escalating to 80, 90 and even 100km per hour. Sometimes, there is hail, too.

While south India experiences a few thunderstorms with occasional hail, the eastern and northeastern regions, as well as parts of West Bengal, experience more frequent hailstorms coupled with intense thunderstorms. This is because their topography allows the cloud layers to extend higher into the atmosphere, with ice-bearing clouds reaching altitudes of up to 10-12 kilometres, especially during severe storms, Raghu says.

To forecast thunderstorms, Raghu and his colleagues look for specific features and indices. The first is the synoptic situation. They assess whether instability is developing due to temperature differences, particularly by analysing the play between the air temperature and the dew point temperature, Raghu explains.

Most importantly, they look for thermodynamic indices of the atmosphere. That is, how much fuel is available for storms to feed on. With land and oceans heating up due to emissions, the atmosphere contains more moisture, wind shear and more CAPE (convective available potential energy).

As per the 2024 monsoon report: “The monsoon season of 2024 was noted for a slow progress in monsoon over north and east India, with a long hiatus during most of June, especially over the Indo-Gangetic plains of India. This was on account of weak monsoon flow, and resulted in below normal convective activity over the northern parts of India. This was reflected in the decreased frequency of thunderstorm activity over most parts of the north and west peninsular India during June. This decreased thunderstorm activity resulted in poor performance of 3 hourly nowcasts but did not affect the 24 hour forecast skill in June. The 24 hour forecast skill in fact deteriorated thereafter and was least in August throughout the country.”

In their paper, published in the journal Urban Climate, Raghu and his colleagues, led by Prof. Dev Niyogi of the University of Texas at Austin, state that by incorporating a realistic representation of anthropogenic fluxes of heat, they found that higher human activity leads to higher variation in storm activity.

In another study, published in the journal Computational Urban Science, they conducted a numerical study over Bhubaneswar to see how thunderstorms are forming; they found that local features—urban agglomeration, the type of material used for building construction, population density, among others—influence thunderstorm activity.

“Urbanisation is altering thunderstorm characteristics,” Raghu says.

They also say that city outskirts are getting more. As Raghu explains, a city has higher temperatures because of the heat island effect, and it sets up a temperature difference between it and the outskirts. The higher, elevated temperatures in the city help clouds dissipate rather than amass; in the outskirts, this is not the case.

Prof. Krishna K. Osuri, National Institute of Technology Rourkela, says that they have known the effects of soil moisture and temperature, especially in central and eastern India, which is more important in predicting these mammoth storms and so they developed a coupled atmosphere-land model that incorporates soil moisture and soil temperature for the whole of India at a very high resolution.

When they ran the model, there was an improvement in the prediction of  thunderstorm activities, especially for the eastern and northeastern regions. They published their results in Nature Scientific Reports on 27 January 2017.

Odisha and West Bengal, eastern Bihar, and the northeast are more prone to thunderstorms. Of these, Angul, Jharsuguda, Mayurbhanj, and such places in Odisha are especially prone. That’s due to their topography, the effect of the Eastern Ghats. The northeast too has high thunderstorm activity due to its topography. There is availability of moisture and hills can lift the hot air up. The combination is a recipe for thunderstorms.

Prof. Osuri says there is a definite effect of climate change on thunderstorms. Because there is so much moisture available, storms can unleash more water. Apart from that, condensation releases heat, which fuels storms more.

To better understand, they are currently working on a U.S.-India collaborative project that integrates ocean, land, and atmosphere variables.  

“The beauty of this particular system development is I can zoom over the thunderstorm region for more accuracy and better understanding,” Osuri says.