BharatNotes What is Loo (Hot Wind)?
The Loo is a strong, gusty, hot and dry wind that blows from the west over the Indo-Gangetic Plain of North India and Pakistan during the pre-monsoon summer, especially in May and June. It is a classic example of a local wind — generated by local temperature and pressure differences rather than the large-scale planetary wind system. Afternoon temperatures in the Loo can reach 45-50°C, and the air is extremely dry, producing a severe drying (browning) effect on vegetation and a high risk of fatal heatstroke.
How the Loo Forms
In May and June the sun shines almost directly overhead in North India. The Thar Desert and surrounding plains heat intensely, creating a thermal low-pressure area. Hot, dry desert air moves toward this low, accelerating into a hot surface wind. Because the air originates over arid land and is heated further as it travels, it arrives with very low humidity and very high temperature. The Loo typically begins by late morning, peaks in the afternoon, and can continue into the evening. It fades with the arrival of the south-west monsoon, whose moist, cooler air ends the season.
Areas Affected and Key Features
The Loo is felt across Punjab, Haryana, Delhi, Rajasthan, Uttar Pradesh, Bihar and Madhya Pradesh, and is most intense near the Thar Desert.
| Feature | Detail |
|---|---|
| Type | Local wind (thermally induced) |
| Direction | From the west / north-west |
| Season | Pre-monsoon summer (chiefly May-June) |
| Time of day | Mainly afternoon, into evening |
| Temperature | ~45-50°C |
| Humidity | Very low (dry wind) |
| Hazard | Heatstroke, dehydration, crop/vegetation drying |
Traditional coping practices in affected regions include drinking aam panna (raw-mango drink) and buttermilk, staying hydrated, wearing loose clothing, and avoiding the outdoors during peak afternoon hours.
Loo and Heat Waves
Severe Loo conditions frequently coincide with official heat-wave alerts. As per the India Meteorological Department (IMD) criteria, a heat wave for the plains is considered when the maximum temperature is at least 40°C (at least 30°C for hilly regions). When the normal maximum is ≤40°C, a heat wave is declared at a departure of 5-6°C above normal (severe at 7°C or more); when actual maximum temperature reaches 45°C or more, a heat wave is declared irrespective of the normal. The condition must be met at two or more stations in a meteorological sub-division for at least two consecutive days.
Distinguish From Related Winds
Do not confuse the Loo with other Indian local winds: andhi are violent dust storms of the north-western plains in summer, while Nor'westers (Kalbaisakhi) are squally pre-monsoon thunderstorms of eastern India (West Bengal, Assam, Bihar) that bring rain rather than dry heat. Western Disturbances are entirely separate — Mediterranean-origin winter weather systems that bring rain and snow to the north-west, not summer heat.
