Delhi mornings colder at about 16°C with more rain due on 29-30 October; winter pollution rules from 1 Nov

The weather was rougher in parts of the neighbouring states. Isolated hailstorms hit central and south Delhi, and hail was reported in Ferozepur in Punjab and in Sirsa, Kurukshetra and Fatehabad in Haryana. Gusts of up to 85 km an hour were recorded in Kaithal. The same system brought fresh snow to high-altitude areas of Jammu and Kashmir, Himachal Pradesh and Uttarakhand.

The IMD said that a weak western disturbance in the middle and upper layers of the atmosphere combined with moisture from the Arabian Sea at lower levels to produce cloud and scattered light rain over Punjab, Haryana and Delhi. The rain that is expected later in the week is linked in one report to a cyclonic system over the Bay of Bengal. The weather office has also warned of heavy rain for Delhi, Haryana, Chandigarh, Punjab and Uttar Pradesh from 28 October to 1 November, in a bulletin that was issued as Cyclone Arnab came ashore in Andhra Pradesh.

Air quality

Rain helped the air. Delhi's 24-hour average air quality index improved by 38 points on Sunday, from 191 on Saturday to 153, which is in the moderate range of 101 to 200. The relief may not last. The air quality early warning system expects the air to slip into the poor category between 26 and 28 October, and then to fluctuate between poor and moderate for the six days that follow.

The Union Environment Ministry and the Commission for Air Quality Management have directed Delhi and the four neighbouring states to strengthen their measures against pollution, and the winter action plan starts across the National Capital Region on 1 November. The measures include mechanical sweeping of roads, sprinkling of water, 100 per cent collection of waste and limits on coal-fired tandoors and diesel generators. Construction and demolition work faces restrictions under the existing guidelines.

In Delhi, commercial and private petrol and diesel vehicles that do not meet BS-VI emission standards will face restrictions from 1 November. Owners of older vehicles should check the rules before they plan trips into the city.

The two forecasts in circulation differ in strength. The weather office's Delhi forecast speaks of light rain around 29 and 30 October, while a wider bulletin issued as Cyclone Arnab came ashore warns of heavy rain over Delhi, Haryana, Chandigarh, Punjab and Uttar Pradesh until 1 November. Residents should check the latest alert from the weather office each day and not rely on one forecast.

A western disturbance is a system of cloud and moisture that moves in from the west, usually from the Mediterranean region, and it brings rain and snow to north India in the cooler months. When it meets moisture from the sea, rain can be heavier, and the clouds and the rain pull the night temperature down because the ground cools after the showers. A change from warm to cool weather in a short time is also the period when colds, coughs and viral fevers become more common, so children and older people should dress in layers.

Light rain is likely around 29 and 30 October, and mornings and evenings should feel colder. People who travel early, especially two-wheeler riders and those who walk, should carry a light jacket and an umbrella. Those with breathing problems should watch the air quality index, since the rain may clear the air for a day or two but the readings are expected to rise again.

Farmers in Punjab and Haryana, where hail and strong winds were reported, may check standing crops for damage, and the state authorities will be the ones to assess losses in the affected areas.