IAS Gyan

Daily News Analysis

Slow winds, clear skies: What’s behind Delhi’s unusually cool October?

1st November, 2020 Geography

Context: With the approaching winter, minimum temperatures in the national capital have trended downward over the last one week.

How is the weather changing in Delhi?

  • Delhi is in the phase of seasonal transition between the southwest monsoon, which has withdrawn from the country, and winter.

What is causing the cooler weather in Delhi?

  • The weather is dry and the sky is mostly clear over North and Northwest India. Gentle northwesterly winds are blowing over the region.
  • Western disturbance developed as a trough at mid-tropospheric level, but did not significantly influence the local weather.

Western disturbance

  • A western disturbance is an extra-tropical storm originating in the Mediterranean region that brings sudden winter rain to the northwestern parts of the Indian subcontinent.
  • It is a non-monsoonal precipitation pattern driven by the westerlies.
  • The moisture in these storms usually originates over the Mediterranean Sea, the Caspian Sea and the Black Sea.
  • Extratropical storms are a global phenomena with moisture usually carried in the upper atmosphere, unlike their tropical counterparts where the moisture is carried in the lower atmosphere.
  • In the case of the Indian subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.
  • Western disturbances are more frequent and strong in winter season.
  • Western disturbances are important for the development of the rabi crop, which includes the locally important staple wheat.