In north India, the Loo is a strong, gusty, extremely hot and dry westerly wind that blows across the north-west and the plains during the daytime in May and June, pushing temperatures above 45 degrees Celsius and causing heatstroke. The word “loo” comes from Hindi, Urdu and Punjabi, and it is one of the oldest named features of the north Indian summer, familiar to anyone who has felt the air turn from warm to scorching on a May afternoon.
The Loo is not a separate weather system so much as the most dangerous face of an Indian heatwave over the dry interior. It blows in the afternoon, fades at night and ends when the monsoon or a dust-and-thunderstorm spell interrupts it. This explainer describes where the Loo comes from, which regions it affects, why it is so harmful to the body, and how people can protect themselves.
| The Loo: Quick Facts | |
|---|---|
| What it is | A hot, dry, gusty daytime wind of the Indian summer |
| Direction | Westerly to north-westerly, blowing from the arid interior towards the plains |
| Season | Mainly May and June, sometimes from late April |
| Time of day | Strongest in the afternoon, from around noon to evening |
| Regions affected | Rajasthan, Punjab, Haryana, Delhi, Uttar Pradesh, Bihar, Madhya Pradesh and parts of Gujarat |
| Temperatures | Daytime maximums commonly above 42 to 45 degrees Celsius, with very low humidity |
| Main health risk | Heatstroke, heat exhaustion and severe dehydration |
| Official monitoring | India Meteorological Department (IMD), which issues heatwave warnings |
| Ends with | Onset of the south-west monsoon or a spell of pre-monsoon thunderstorms |
Key Takeaways
- The Loo is a hot, dry westerly wind that blows over north-west and north India in May and June, and it is strongest in the afternoon.
- The Loo forms because intense heating of the Thar Desert and nearby plains builds a heat low and draws dry, hot air across the region.
- Exposure to the Loo can cause heatstroke, a medical emergency in which body temperature rises above about 40 degrees Celsius and the brain and organs begin to fail.
- The Loo is dry heat, which means sweat evaporates quickly and the body loses water fast, often without the victim noticing how dehydrated they have become.
- People can reduce Loo-related risk by avoiding outdoor work between noon and 4 pm, drinking fluids regularly, and wearing loose, light cotton clothes with a head covering.
- The Loo usually weakens when moist monsoon air or a thunderstorm brings cooler, humid conditions to the plains.
What Exactly Is the Loo?
The Loo is a hot, dry, westerly wind of the Indian pre-monsoon summer that blows over the plains of north-west and central India, usually between noon and evening. It is felt as a blast of furnace-like air, often with dust, and it can raise the apparent heat so strongly that standing in the open becomes painful within minutes.
The wind is a regional name rather than a formal meteorological category, much like the “Chinook” or the “Santa Ana”. In weather reports, the Loo is covered by the IMD’s heatwave warnings, and when someone says “Loo lag gayi” in north India, the person means a heatstroke caused by this wind. Folk practices around summer drinks, midday rest and wet cloth head coverings have grown up because of it.
Why Does the Loo Blow in North India?
The Loo blows because strong summer heating creates a zone of low pressure over north-west India, and air rushes in from the dry west to fill it. By May the sun is almost overhead, and the Thar Desert and neighbouring plains absorb enormous energy during the day. The hot ground heats the air above it, which rises and leaves lower pressure near the surface.
This area of low pressure is commonly called the heat low, and it deepens as the pre-monsoon season advances. Surrounding air flows towards it, and over the arid west the air coming in has very little moisture. Because it passes over bare, sun-baked land, it gets hotter on the way. The result is a dry, westerly flow with surface temperatures that can exceed 45 degrees Celsius, and humidity that can fall to single digits in the afternoon.
Why the Loo is strongest in the afternoon
The Loo peaks in the afternoon because ground temperature climbs through the morning and reaches its maximum between about 2 pm and 4 pm. As the day heats, vertical mixing grows, and faster winds from higher in the atmosphere are brought down to the surface. That adds the gusty character of the Loo. At night the ground cools, mixing dies down and the wind drops, though in intense spells even the nights stay uncomfortably warm.
The role of the dry upper-level air
Dry air aloft keeps the sky clear and lets the sun heat the land without interruption. Dust and haze often carry in from the desert, which is why the Loo can bring a hazy, brownish sky. Without moisture, there is little cloud to shield the surface, and the heat builds day after day.
Which Regions of India Are Hit by the Loo?
The Loo mainly affects the north-west and north Indian plains, with its core over Rajasthan, Punjab, Haryana, Delhi and Uttar Pradesh, and it extends to Bihar, Madhya Pradesh and Gujarat in strong spells. Western Rajasthan, home to the Thar Desert, has some of the highest temperatures in the country.
- Rajasthan: Phalodi recorded 51.0 degrees Celsius on 19 May 2016, the highest temperature officially recorded in India, and towns such as Barmer, Jaisalmer, Churu and Sri Ganganagar regularly cross 47 degrees.
- Punjab, Haryana and Delhi: Dry heat builds across the plains in May, and the Delhi region regularly sees maximums near or above 45 degrees in the worst spells.
- Uttar Pradesh and Bihar: The Loo blows across the Gangetic plain, and cities such as Banda, Prayagraj and Varanasi become some of the hottest in the country.
- Madhya Pradesh and Vidarbha: Central India is hot in May, though the wind is generally less strong than in the north-west.
Coastal and eastern regions are usually less exposed to the Loo, because moist sea air limits the dryness and the wind. They suffer a different form of heat stress, with high humidity making the air feel oppressive even at lower temperatures.
How Does the Loo Cause Heatstroke?
The Loo causes heatstroke when the body can no longer lose heat as fast as it gains it, so its core temperature climbs beyond the safe range. Normally, sweat evaporates from the skin and carries heat away. In a Loo, the air is so hot and the wind so strong that the body gains heat from the surroundings, and sweat evaporates so fast that the person can lose large amounts of water without feeling wet.
Stages of heat illness
| Condition | Signs | What to do |
|---|---|---|
| Heat cramps | Painful muscle spasms in legs, arms or abdomen, heavy sweating | Rest in shade, drink water or oral rehydration solution (ORS) |
| Heat exhaustion | Fatigue, dizziness, headache, nausea, cool and clammy skin, rapid pulse | Move to a cool place, loosen clothes, sip fluids, cool the skin with wet cloth |
| Heatstroke | Body temperature above about 40 degrees Celsius, hot and often dry skin, confusion, fits, collapse | Emergency: cool the person quickly and call 108 or 112 at once |
Heatstroke is dangerous because it can damage the brain, heart, kidneys and muscles within a short time, and death can occur if the body is not cooled quickly. Older people, infants, pregnant women, people with heart, kidney or diabetic conditions, and those on certain medicines are at higher risk.
Who Is Most Vulnerable to the Loo?
Outdoor workers, the elderly, young children and the urban poor are the most vulnerable to the Loo, because they have the greatest exposure or the least ability to cool down. Farm labourers, construction workers, street vendors, rickshaw pullers, traffic police and delivery workers spend long hours in the afternoon sun.
Homes also matter. Families living under tin or asbestos sheets, in cramped slum housing, or without fans, coolers or reliable power cannot escape the heat even indoors. Power cuts during heatwaves add to the risk. Livestock and wild animals suffer too, with birds and cattle sometimes dying in extreme spells.
How Can You Protect Yourself From the Loo?
The most effective protection from the Loo is to avoid outdoor exposure in the hottest hours, drink fluids regularly, and keep the body cool. The Ministry of Health and Family Welfare and the National Disaster Management Authority (NDMA) publish summer advisories that follow the same principles.
- Stay indoors in the afternoon: Avoid going out between about noon and 4 pm unless essential, and plan work for early morning or evening.
- Drink before you feel thirsty: Take water, buttermilk (chaas), lassi, lemon water, coconut water and ORS through the day, and avoid alcohol, tea, coffee and sugary fizzy drinks in excess.
- Dress for the heat: Wear light-coloured, loose cotton clothes, and cover the head with a cap, scarf or umbrella. Use a damp cloth around the neck if working outdoors.
- Keep homes cool: Close curtains on sun-facing windows by day, open windows at night, and use fans, wet curtains or coolers where available.
- Never leave anyone in a parked vehicle: The interior of a closed car can reach dangerous temperatures within minutes, and children and pets must not be left inside.
- Look after others: Check on elderly neighbours and children, and give outdoor workers shade and water breaks.
Traditional remedies
Traditional drinks such as aam panna, made from raw mango, and sattu drinks are widely used to stay hydrated and replace salts during the north Indian summer. Many families also carry a raw onion or wrap a wet cloth around the head. Aam panna and sattu are nutritious and refreshing, but there is little formal clinical evidence that an onion prevents heatstroke, so these folk practices should supplement rather than replace shade, fluids and rest.
What Should You Do If Someone Gets Heatstroke?
If someone shows signs of heatstroke, call an ambulance on 108 or 112 immediately and start cooling the person without delay. Heatstroke is a medical emergency, and every minute of delayed cooling raises the risk of lasting damage.
- Move the person to a shaded or air-conditioned place and lay them down with the legs slightly raised.
- Remove extra clothing and cool the body with wet cloths, a wet sheet, a fan or by sponging the neck, armpits and groin.
- If the person is conscious and able to swallow, give small sips of water or ORS. Do not force fluids on someone who is confused or unconscious.
- Do not give medicines such as paracetamol to lower the temperature, because heatstroke is not caused by a fever and these medicines do not help.
- Continue cooling until medical help arrives and take the person to a hospital even if they seem to recover.
How Does the Loo Differ From a Heatwave?
The Loo differs from a heatwave in that the Loo is a specific hot, dry wind, while a heatwave is an official weather condition defined by temperature thresholds. A heatwave can occur without a strong wind, and the Loo can blow on days that fall just short of the formal heatwave criteria.
In practice the two overlap heavily. A heatwave in the north Indian plains is nearly always accompanied by the Loo, and public warnings often use both terms. The IMD declares a heatwave when the maximum temperature in the plains reaches at least 40 degrees Celsius and is several degrees above normal, or when it crosses 45 degrees outright. The Loo is the lived experience of that heat: the hot gust on the face and the dry air in the throat.
Is the Loo Getting Worse?
The Loo is probably being intensified by warming, because longer and hotter heatwaves in the north Indian plains have been observed over recent decades. The IMD and independent climate studies point to a rising number of heatwave days in north-west India, and early heat in March and April has become more common.
Urban growth adds to the burden. Concrete, asphalt and the lack of trees raise city temperatures above those in surrounding countryside, and heat in the night reduces recovery time. Heatwave years such as 2015 and 2022 saw long dry spells across the north and many reported deaths. Exact long-term trends depend on location, but the direction is toward more frequent and prolonged dangerous heat.
When Does the Loo End?
The Loo ends when moist air from the south-west monsoon or a pre-monsoon thunderstorm spell brings humidity and cloud to the plains. Western disturbances and dust storms (andhi) can also interrupt the Loo for a few days, cooling the temperature and clearing the heat for a short time.
The monsoon usually reaches Kerala around the start of June and advances north, arriving in Delhi and north-west India in late June or early July. Until then, the final weeks before the monsoon can be among the hottest. The relief from the monsoon is tempered by humidity, which brings its own form of heat stress.
Bottom Line
The Loo is the hot, dry wind that defines the north Indian summer, and it is dangerous because it can overwhelm the body quickly. Staying indoors at midday, drinking fluids, covering the head and acting fast against heatstroke can keep most people safe until the monsoon arrives.
Frequently Asked Questions
What is the Loo in India?
The Loo is a hot, dry, gusty westerly wind that blows across north-west and north India in May and June. It is strongest in the afternoon and can push temperatures above 45 degrees Celsius. The wind is a major cause of heatstroke in the region.
Why is the Loo so hot and dry?
The Loo is hot and dry because it forms over the Thar Desert and nearby plains, where strong summer sun heats the ground and builds a low-pressure zone. Dry air from the west flows in to fill that low and heats further as it travels over bare land. Little moisture is present, so humidity can fall very low.
What is the best way to protect yourself from the Loo?
The best way to protect yourself from the Loo is to avoid going out between noon and 4 pm, drink fluids regularly and wear loose cotton clothes with your head covered. Keep indoor spaces cool and check on children and older people. Seek medical help at once if anyone shows confusion or collapses.
What are the signs of heatstroke from the Loo?
The signs of heatstroke include a body temperature above about 40 degrees Celsius, hot and often dry skin, a rapid pulse, headache, confusion, fits and fainting. It is an emergency. Call 108 or 112 and cool the person quickly while waiting for help.
Which Indian states are affected by the Loo?
The Loo mainly affects Rajasthan, Punjab, Haryana, Delhi, Uttar Pradesh and Bihar, and it extends to Madhya Pradesh and Gujarat in strong spells. Western Rajasthan, including Phalodi, which recorded the national high of 51 degrees Celsius in 2016, is among the hottest areas. Coastal regions are generally less affected by this dry wind.
When does the Loo stop?
The Loo stops when the monsoon or a pre-monsoon thunderstorm brings moist air and cloud to north India. The monsoon usually reaches the north-west plains in late June or early July. Dust storms and western disturbances can give short breaks earlier.
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