Some hilly areas of Koshi, Bagmati and Gandaki provinces are most likely to witness light rainfall on Monday, as a western disturbance originating in the Mediterranean is bringing a change in the ongoing weather system.

The Meteorological Forecasting Division of the Department of Hydrology and Meteorology said that most parts of the country could witness light rainfall on Tuesday and Wednesday as well.

“High hills and mountainous areas will witness snowfall and the rest of the countries will witness rainfall on Tuesday and Wednesday,” said Saroj Pudasaini, a meteorologist at the division. “This rainfall will lessen minimum temperature, meaning that cold will increase, lessen the dust pollution and remove fog and mist in the Tarai region.”

Districts of the Tarai region have been witnessing thick fog in the morning for the last several days, which has also affected domestic flights and vehicular movements.

Earlier, districts in the Sudurpaschim and Karnali provinces witnessed rainfall on December 5.

A lack of rainfall for a long time has raised the pollution level in the country.

On Sunday, the Kathmandu Valley ranked the 11th most polluted city in the world with PM2.5 levels reaching 170 per cubic meter (μg/m3), as per IQ Air, a Swiss group that collects air-quality data from around the world.

Experts say that when air quality reaches 151–200, it is considered unhealthy; everyone may experience problems, with sensitive groups feeling more severe effects.

When the Air Quality Index exceeds 300, it is considered “hazardous” for everyone and may prompt emergency condition alerts.

An elongated dry spell has made the year 2023 the warmest in Nepal in 13 years and the second warmest in the past 42 years.

According to the Department of Hydrology and Meteorology, which maintains records of temperature, precipitation and other meteorological activities, the country received lower-than-normal precipitation, with the average maximum temperature rising above 0.7 degrees Celsius between January and October last year.

“The average maximum temperature of the country during January to October was 28 degrees Celsius, which is the second warmest year since 1981. It was +0.7 degrees Celsius above normal,” said Sudarshan Humagain, a meteorologist at the department. “In 2010, the average maximum temperature was 28.1 degrees Celsius.”

Officials say that the final data for November and December is yet to be updated, which could make some difference in calculating average temperature increase.

A report prepared by the department states that during the same 10 months, the country received 11 percent lower-than-normal rainfall, which is the sixth lowest precipitation since 1981. The average maximum temperature from January to October was 0.7°C above normal. The average minimum temperature in the period was 0.2°C above normal.

This year, several stations broke previous records of extreme temperature and precipitation. Bandipur in Tanahun, Chatara in Sunsari, Chautara in Sindhupalchok, Dharan Bazaar in Sunsari, Damkauli in Nawalparasi East, Gorkha, Janakpur Airport of Dhanusha, Kanyam Tea Estate of Ilam, Okhaldhunga, Chitwan, Simara Airport of Bara, and Siraha recorded extreme temperatures.

Evidence indicates that the maximum temperature in Nepal is rising at a greater rate (0.05 degrees Celsius per year) than the minimum temperature (0.03 degrees Celsius per year).

Experts say extreme weather events—excessive rainfall in a short span of time, continuous rain for several days in the post-monsoon period, dry spells and droughts, below-average precipitation and above-normal temperatures in winter—have become more frequent in Nepal.