A wall of dust is forecast to sweep across the Delhi-NCR skyline in the next two hours. (Photo: PTI)

Dust storm to hit Delhi-NCR with 70 kmph winds, lightning and rain in next 2 hours

A wall of dust is forecast to sweep across Delhi-NCR within the next two hours, with thunder, lightning and rain to follow. Here is the simple science behind the aandhi, the fierce pre-monsoon dust storm that hits northwest India every summer.

by · India Today

In Short

  • Dust storm, thunderstorms and rain are forecast to hit Delhi-NCR.
  • Aandhi forms when storm downdrafts lift desert dust into walls.
  • IMD warns of fifty to seventy kilometre winds over Delhi.

A towering wall of dust is set to sweep across Delhi and the National Capital Region (NCR) within the next two hours, with thunder, lightning and rain expected to follow.

The India Meteorological Department has warned of a dust storm trailed by thunderstorms, with winds of 50 to 70 kilometres per hour.

WHAT IS AN AANDHI, AND WHY DOES DELHI GET ONE?

Aandhi is the local name for the violent pre-monsoon dust storms that hit northwest India in late May.

Fierce summer heat warms the ground and makes the air unstable, the fuel storms feed on.

Pre-monsoon aandhis are common over northwest India in late May. (Photo: PTI)

Dry, loose soil from Rajasthan and the Thar Desert supplies the dust.

HOW DOES A DUST STORM BECOME A THUNDERSTORM?

Inside a growing storm cloud, cool air plunges towards the ground in a downdraft.

When it lands, it spreads outwards as a gust front, a sudden rush of wind that scoops soil into a moving wall, also called a haboob.

Dust storm to hit Delhi-NCR with 70 kmph winds, lightning and rain in next 2 hours

The same tall cloud then releases its rain.

WHY IS THERE SO MUCH LIGHTNING?

High up, ice crystals and water droplets smash together and swap electric charge.

Lighter positive charges gather at the top and heavier negative ones sink to the base.

When the gap grows large enough, it snaps as a lightning bolt, and the air it heats expands to give the thunderclap.

HOW DO SATELLITES SPOT THESE STORMS COMING?

Forecasters watch water vapour satellite images, which sense moisture in the middle and upper atmosphere.

Dark patches show dry air higher up, while bright white areas reveal damp air or tall storm clouds.

These pictures also trace the high winds and jet streams that steer and organise the storms.

WILL THIS BRING RELIEF FROM THE HEAT?

The IMD says the heat wave has eased over central India, and Delhi's maximum is several degrees below normal, around 36 to 38 degrees Celsius.

The rain also marks the advancing southwest monsoon, though a below normal season is expected, near 90 per cent of the long period average, as El Nino builds.

(With inputs from Anmol Nath Bali)

- Ends