The IMD has put Delhi-NCR under an orange alert, with a light thunderstorm, lightning and 40 to 60 kmph winds likely within the next 2 hours. (Photo: PTI)

Rain in Delhi-NCR likely: IMD issues orange alert, gusty winds on approach

The India Meteorological Department has placed Delhi-NCR under an orange alert, with a light thunderstorm, lightning and gusty winds likely within two hours. Here is the science behind the sudden storm, what an orange alert really means and how to stay safe.

by · India Today

In Short

  • IMD issues orange alert for moderate thunderstorm across Delhi-NCR districts.
  • Light thunderstorm and lightning likely in Delhi-NCR within two hours.
  • Gusty winds of 40 to 60 kilometres per hour expected.

The Delhi sky did not wait for the monsoon to announce itself. By late afternoon on June 28, the clouds had thickened over the capital, and the India Meteorological Department (IMD) had a warning ready.

At 3.30 pm, its bulletin said light rainfall with a light thunderstorm, lightning and gusty winds of 40 to 60 kilometres per hour was very likely across the whole of Delhi and the National Capital Region (NCR) within the next two hours.

By 4.10 pm, a district-level nowcast, a very short-range forecast for the hours immediately ahead, had pushed several districts into an orange alert.

WHAT IS AN ORANGE ALERT FROM THE IMD?

The IMD grades weather risk with four colours. Green means no warning. Yellow asks you to stay updated.

Orange, the level Delhi is under now, means be prepared: a moderate thunderstorm with lightning and winds of 40 to 60 kilometres per hour is on the way.

The IMD district-level nowcast for June 28 shades much of Delhi orange, flagging the likelihood of a moderate thunderstorm with lightning by 7:10 pm IST. (Photo: PTI)

Red, the most serious, means taking action against severe weather.

Orange is not a reason to panic. It is a nudge to bring in loose objects, step indoors and keep an eye on the sky.

WHY IS DELHI GETTING A THUNDERSTORM RIGHT NOW?

Late June is the handover between fierce pre-monsoon heat and the arriving southwest monsoon, and Delhi has been baking at 41 to 43 degrees Celsius.

That heat is the fuel. As the hot ground warms the moist air above it, the air turns buoyant and shoots upward.

Scientists measure this stored energy as convective available potential energy, or CAPE, which is simply how much lift the atmosphere has waiting to be released.

Fierce June heat and incoming monsoon moisture feed towering cumulonimbus clouds, the engines that drive Delhi's sudden evening storms. (Photo: PTI)

Two more ingredients finish the recipe. Moist winds drifting in from the Bay of Bengal and the Arabian Sea supply the water.

A western disturbance, a band of moisture-bearing winds that travels from the Mediterranean across north India, gives the air an extra shove upward.

Together, they build cumulonimbus clouds, the towering, anvil-topped storm clouds that can climb more than 10 kilometres high.

WHAT DOES THE WEATHER RADAR ACTUALLY SHOW?

The animated radar loop doing the rounds comes from a Doppler weather radar, an instrument that fires radio waves at clouds and reads what bounces back.

The bright blobs are not paint. They show reflectivity on a scale called dBZ, which measures how heavily a cloud is raining. Blues are light rain. Yellows and oranges are the intense cores where rain is heaviest and updraughts are strongest.

Watching them grow and drift is how forecasters time a storm.

Rain in Delhi-NCR likely: IMD issues orange alert, gusty winds on approach

The gusty winds come from cool air crashing down out of these clouds and spreading along the ground as a gust front.

Lightning is born when ice crystals and soft hail collide inside the cloud, separating electrical charge until it leaps free in a flash.

It is, in short, a textbook late-June Delhi storm. Brief, dramatic and, for a few hours at least, a welcome break from the heat.

- Ends