If viewed from space on the morning of July 19, much of India would have appeared hidden beneath an expansive blanket of monsoon clouds.
Satellite imagery captured that day showed a broad swathe of cloud cover stretching from Jammu and Kashmir across the Gangetic plains and extending into the northeastern states, highlighting the widespread influence of the southwest monsoon.
How Much of India Was Under Cloud Cover?
An assessment of visible satellite imagery alongside infrared observations from the INSAT-3DR weather satellite indicates that approximately 60 to 70 per cent of India's land area was covered by clouds on July 19.
The densest cloud formations were concentrated over the northern plains, extending from Punjab through Uttar Pradesh, Bihar and West Bengal, as well as across much of the Northeast. Long bands of monsoon clouds also spread over peninsular India, sustained by moisture-laden winds arriving from the Arabian Sea.
In contrast, western Rajasthan and parts of Tamil Nadu remained relatively clear. The estimate represents a snapshot in time, with cloud cover naturally changing throughout the day as weather systems develop and dissipate.
How Do Weather Satellites Detect Clouds?
The INSAT-3DR weather satellite, developed by the Indian Space Research Organisation (ISRO), continuously monitors the Indian subcontinent from a geostationary orbit approximately 36,000 kilometres above the equator.
Because it remains fixed over the same location relative to Earth, the satellite is able to capture updated images of the region every 30 minutes. The India Meteorological Department (IMD) relies extensively on these observations for weather monitoring and forecasting.
INSAT-3DR observes clouds using two primary imaging systems.
The visible imaging channel functions like a conventional camera, recording sunlight reflected from the Earth's surface and cloud formations. Thick clouds appear brighter because they reflect more sunlight.
The thermal infrared channel operates differently. Rather than detecting visible light, it measures heat emitted by clouds at a wavelength of 10.8 micrometres, allowing observations both during the day and at night. This helps meteorologists estimate the temperature at the top of cloud formations.
Understanding Cloud Top Brightness Temperature
Cloud Top Brightness Temperature (CTBT) refers to the temperature of the upper surface of a cloud as measured by a weather satellite. It does not represent the air temperature experienced at ground level.
Since atmospheric temperature generally decreases by about 6.5 degrees Celsius for every kilometre of altitude, colder cloud tops indicate taller cloud formations.
Cloud tops colder than minus 40 degrees Celsius typically signify deep thunderclouds, while temperatures below minus 70 degrees Celsius indicate extremely powerful storm systems reaching close to the upper boundary of the troposphere.
The CTBT imagery from July 19 revealed exceptionally cold cloud tops—below minus 80 degrees Celsius—over Jammu and Kashmir. Additional areas with cloud-top temperatures below minus 50 degrees Celsius were observed across Uttar Pradesh, Bihar, Jharkhand, the northeastern states, and parts of Karnataka, Telangana and Andhra Pradesh.
These extremely low temperatures suggest the presence of intense convective storms capable of producing heavy rainfall.
Does Extensive Cloud Cover Mean It Is Raining Everywhere?
Not necessarily.
Although nearly two-thirds of the country was covered by clouds, much of that consisted of thin high-altitude cirrus clouds or widespread monsoon overcast that produces little or no rainfall.
Heavy precipitation occurs primarily beneath the deepest convective storm systems, which occupy only a relatively small proportion of India's total land area at any given time.
The coldest cloud tops, measuring below minus 80 degrees Celsius, correspond to towering thunderstorms over Jammu and Kashmir, the Gangetic plains and the northeastern region, where the most intense rainfall activity was concentrated.
These powerful storms are sustained by the enormous amount of energy released during condensation. Every kilogram of water vapour that condenses into liquid water releases roughly 2.5 million joules of latent heat, strengthening upward air currents and allowing storm clouds to grow to heights of around 15 kilometres.
With the monsoon trough currently active across northern India, these atmospheric processes continue to support widespread cloud development and vigorous thunderstorm activity across large parts of the country.
