Knowledge Nugget | What are Western Disturbances?

Let’s understand the mechanism of western disturbances, various alerts issued by the IMD, and new initiatives for improving weather forecasting in India.

Key takeaways:

1. Western disturbances are rain-bearing wind systems, originating beyond Afghanistan and Iran, that pick up moisture from the Mediterranean Sea, the Black Sea, the Caspian Sea and the Arabian Sea as they move eastward towards India.

2. Western Disturbances trigger rain (and snowfall in higher altitudes) in the northwest, north, northeast and some parts of eastern India during the non-monsoon months (June-September). This also holds true for early March, when the effect of winter is still lingering.

3. As India is transitioning from cold weather season to hot weather season, several changes are happening in the direction of trade winds, change in temperature, pressure, and western cyclonic disturbances.

4. According to NCERT, along with latitude and altitude, pressure winds that include surface winds, Upper air circulation; and  western cyclonic disturbances and cyclonic disturbances affect India’s climate.

5. During the cold weather season which generally begins from mid-November in northern India and stays till February, the northeast trade winds prevail over the country. They blow from land to sea and hence, for most parts of the country, it is a dry season.

6. The inflow of cyclonic disturbances from the west and the northwest is one of the characteristic features of the cold weather season over the northern plains. They bring the much-needed winter rains over the plains and snowfall in the mountains. This winter rainfall is locally known as ‘mahawat’ which is important for the cultivation of ‘rabi’ crops.

7. The peninsular region of India does not have a well-defined cold season. There is hardly any noticeable seasonal change in temperature pattern during winters due to the moderating influence of the sea.

What changes with the advent of the hot weather season?

8. Generally, March to May is the hot weather season in India. The global heat belt shifts northwards with the apparent northward movement of the Sun. This leads to an increase in temperature in the northern plains. A temperature of 45 degree celsius is common in the northwestern part of the country in the month of May. In peninsular India, temperatures remain lower due to the moderating influence of the oceans.

(AI-generated)

9. As per the NCERT, the strong, gusty, hot dry winds called ‘loo’ are one of the striking features of the hot weather season. Along with this, dust storms are also common in the month of May in northern India, which brings temporary relief. The localised thunderstorms in West Bengal are known as the ‘Kaal Baisakhi’ or Nor’westers.

10. Towards the close of the summer season, pre-monsoon showers are common, especially in Kerala and Karnataka. They help in the early ripening of mangoes, and are often referred to as ‘mango showers’.

BEYOND THE NUGGET: IMD’s weather forecasting system

1. Since 2003, the IMD has been using INSAT data for its operational meteorology purposes. The advent of satellite-based products brought significant improvements in the forecast accuracy, monitoring of atmosphere and ocean parameters and overall enhanced the meteorological services, leading to a reduction in loss to property, life, and livelihood.

2. Satellites: India has three satellites in space — INSAT-3D, INSAT-3DR, and INSAT-3DS —that are used mainly for meteorological observations. Of these, INSAT-3D and INSAT-3DR have been in space for over 8 years, and nearly completed their mission lives. INSAT-3DS was launched in 2024.

3. Monsoon Mission: The IMD has launched several key initiatives aimed at improving its capabilities. One of its flagship initiatives is the Monsoon Mission, an extensive programme that uses advanced Numerical Weather Prediction (NWP) models powered by High-Performance Computing (HPC) to effectively forecast monsoon rainfall across various time scales.

4. BFS: IMD officially adopted the Bharat Forecast System (BFS) – a new indigenously built weather model developed by the Indian Institute of Tropical Meteorology (IITM) – on 26th May 2025.

5. This model features a high spatial resolution of 6km x 6km, providing forecasts for units of 36 sq km – a significant leap from the existing 12km x 12km resolution model, which covered a 144 sq km area as a single unit. The BFS is expected to significantly improve the accuracy of IMD’s forecasts and enable precision forecasting even at the Panchayat level.

6. Mission Mausum: Yet another notable initiative is the Mission Mausum. On the occasion of 150 years of IMD in service, Mission Mausam was inaugurated by Prime Minister Narendra Modi on January 14. It aims to upgrade the capabilities of India’s weather department in forecasting, modelling, and dissemination. It has a budget outlay of Rs 2,000 crore for the first two years of its implementation.

Post Read Question

Consider the following pairs:

1. Kaal Baisakhi: localised thunderstorms in West Bengal

2. Mahawat: winter rainfall in north India

3. Mango showers: pre-monsoon showers of Kerala

How many of the above pairs are correct?

(a) Only one

(b) Only two

(c) All three

(d) None

(Sources: NCERT Geography, How IMD became central to India’s climate and disaster preparedness, India’s weather forecasting)

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