Monsoon playing hide and seek: Why some clouds rain, and others don't

India's monsoon has slowed sharply even as clouds persist across many regions. The pause reflects weak atmospheric lift, leaving a 64% rainfall deficit in mid-June.

In Short

• India logged 19.2 mm rain against a normal 53.7 mm
• The nationwide rainfall deficit stood at 64% between June 4 and 15
• Cumulus and stratus clouds usually lack the growth needed for downpours

The southwest monsoon has hit a major roadblock, with satellite imagery revealing a sharp decline in cloud activity across much of India despite recent advances into southern and central regions.

According to IMD data, India recorded just 19.2 mm of rainfall between June 4 and June 15 compared to the normal 53.7 mm, resulting in a nationwide rainfall shortfall of 64%.

As the southwest monsoon struggles to gain momentum across India, many people are looking up at the sky and asking a simple question: if there are clouds overhead, why isn't it raining?

The answer lies in the complex physics of cloud formation, atmospheric moisture and air movement. Not all clouds are created equal, and only a small fraction are capable of producing significant rainfall.

WHAT ARE THE TYPES OF CLOUDS?

Meteorologists classify clouds into several types, each with different rainfall potential.

Cumulus clouds, the fluffy cotton-like clouds often seen on sunny days, generally do not produce rain. They form due to localised heating near the ground and are usually shallow.

Stratus clouds are flat, grey layers that blanket the sky. They may produce light drizzle but rarely generate heavy rainfall because they lack strong vertical growth.

The real rain-makers are cumulonimbus clouds. These towering thunderstorm clouds can rise more than 15 kilometres into the atmosphere and contain powerful updrafts that help droplets grow rapidly. They are responsible for intense monsoon downpours, thunderstorms, lightning and even hail.

Another important monsoon cloud type is nimbostratus, which produces widespread, steady rain over large areas without the dramatic thunder and lightning associated with cumulonimbus clouds.

HOW DO RAIN CLOUDS FORM?

Clouds form when warm, moist air rises and cools. As the air cools, water vapour condenses onto tiny particles such as dust, salt or pollution, creating billions of microscopic water droplets. However, the presence of cloud droplets alone does not guarantee rain.

For rainfall to occur, these droplets must collide and merge into larger drops. Once the droplets become heavy enough to overcome the upward motion of air, they begin falling as rain.

If the droplets remain too small, the cloud may simply drift away or evaporate without producing precipitation.

India's current monsoon slowdown highlights another key factor: atmospheric conditions above the clouds.

Meteorologists say a southward shift of the westerly jet stream has disrupted the upper-level easterly jet that normally supports monsoon circulation. As a result, air is not rising vigorously enough over many regions, preventing clouds from growing into rain-bearing giants.

In other words, moisture is available, and clouds are present, but the atmosphere is not providing the lift needed to transform them into effective rain producers.

Until stronger upward motion returns to the atmosphere, many of India's clouds may continue to look impressive without delivering the widespread monsoon rains farmers and cities are waiting for.

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