Most parts of the country except the districts of Madhesh and Koshi Province witnessed cloudy weather conditions on Monday causing delays in several domestic flights.

According to the Meteorological Forecasting Division of the Department of Hydrology and Meteorology, westerly winds, responsible for the cloudy conditions, are also causing light rainfall and snowfall in several places of Gandaki, Lumbini and Karnali provinces.

“Rainfall has been continuing in the western region,” said Shanti Kandel, a meteorologist at the division. “Snowfall occurred in the high hills and mountainous regions of Gandaki, Lumbini and Karnali.”

The weather system, which is moving from west to east, will reach Madhesh and Koshi provinces Monday night. Some places of Bagmati, Gandaki, and Lumbini could witness light rainfall on Monday night as well, according to the meteorologist.

The change in the weather system also worsened the air quality of the Kathmandu Valley reaching an unhealthy level, which raises serious public health concerns.

According to IQAir, the Swiss air quality technology company, air pollution in Suryabinayak of Bhaktapur has risen with the PM2.5 level reaching 177. The air quality level of Kathmandu reached 158.

IQAir collects real-time air-quality data from around the world. PM 2.5 refers to particulate matter or solid and liquid droplets in the air that are less than 2.5 micrometres, or 400th of a millimetre, in diameter. As per the United States Environment Protection Agency’s air quality index, when PM2.5 reaches 151 to 200 μg/m3, air quality is considered unhealthy; everyone may experience problems, with sensitive groups feeling more severe effects.

Although a decline in air quality during winter and dry seasons is a common phenomenon, a sudden rise in air pollution levels is alarming, public health experts say.

“Weather will improve on Tuesday from the western region, but there will be clouds in the rest of the provinces,” said Sanjeev Adhikari, a meteorologist at the division. “Minimum temperature will decline in the western region after the improvement in the weather. Maximum temperature will decline in Madhesh and Koshi Province on Tuesday due to cloudy conditions.”

Met officials said that a cyclone developed in the Bay of Bengal will bring clouds to Koshi Province on Tuesday, which could also cause snowfall in the high hills and mountains.