Slow winds, clear skies: What’s behind Delhi’s unusually cool October?
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- Delhi is in the phase of seasonal transition between the southwest monsoon, which has withdrawn from the country, and winter.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.
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