**Answer:**

**Introduction:**
Snowfall in the Himalayas during the winter season is primarily caused by western disturbances. Western disturbances are extratropical storms that originate in the Mediterranean Sea and travel eastwards. These disturbances bring rain and snowfall to various regions, including the Himalayas, during the winter season.

**Explanation:**

1. **Western disturbances:** Western disturbances are low-pressure systems that develop over the Mediterranean Sea and move eastwards towards the Indian subcontinent. They are responsible for the winter rainfall and snowfall in the Himalayas. These disturbances bring moisture and cold air from the Mediterranean region, and as they move over the Himalayas, they cause precipitation in the form of snow.

2. **Interaction with the Himalayas:** As western disturbances approach the Himalayas, they interact with the topography and atmospheric conditions of the region. The Himalayas are a significant barrier that forces the air to rise, leading to the condensation of moisture and the formation of clouds. The rising air cools, and the moisture in the clouds condenses, resulting in precipitation in the form of snowfall.

3. **Effect of temperature inversion:** During the winter season, temperature inversion occurs in the Himalayan region. Temperature inversion refers to a situation where the temperature increases with altitude instead of decreasing. This inversion layer traps the cold air near the surface and prevents it from mixing with the warmer air above. As a result, the cold air remains closer to the ground, creating favorable conditions for snowfall.

4. **Advancing monsoon and retreating monsoon:** While both the advancing and retreating monsoons bring rainfall to the Himalayas, they are not the primary cause of snowfall during the winter season. The advancing monsoon occurs from June to September, bringing rain to the Himalayas, but not snowfall. The retreating monsoon occurs from October to December and may bring some rainfall, but it is not the primary cause of snowfall in the Himalayas.

5. **Bay of Bengal Branch:** The Bay of Bengal Branch of the monsoon is associated with rainfall in the northeastern parts of India and the eastern slopes of the Himalayas. However, it is not the primary cause of snowfall in the Himalayas during the winter season.

In conclusion, snowfall in the Himalayas during the winter season is primarily caused by western disturbances. These disturbances bring moisture and cold air from the Mediterranean region, and as they interact with the topography and atmospheric conditions of the Himalayas, they cause precipitation in the form of snowfall.

Western disturbances...