It could now be a race against the South-West monsoon for the government and multilateral agencies engaged in relief and rescue operations in quake-hit Nepal.

Already, afternoon thunderstorms intervene in these efforts mounted most notably by neighbouring India and aid agencies which have to battling both the weather and occasional aftershocks.

Western disturbances

The main weather-triggering feature is the western disturbance that travels from west to east over Pakistan, north-west India and east and north-east India.

One such is perched over eastern Jammu and Kashmir, according to an India Met Department update on Tuesday.

It is expected to move away to the east by Wednesday, but would have sent ripples across the Himalayas into Nepal to trigger rain and thundershowers.

Another western disturbance is expected to impact the western Himalayan region from Thursday, the Met Department said, with implications for downstream Nepal.

Monsoon onset

The weather has added to the discomfort after relief operations were slowed down by the inability of the small airport to handle aircraft flying in men and material.

In the medium to long term, it should be the onset of monsoon over a landscape ploughed by the massive M7.9 quake that should worry the Nepalese government.

The seasonal rain first reaches the Himalayan ranges over Bhutan, Sikkim and eastern Nepal, where it arrives the earliest and stays the longest.

The eastern Himalayas consequently receive the highest total precipitation during the year.

The monsoon sets in from the east and the normal onset date is June 10 for eastern Nepal and June 12 for Kathmandu. It is closely intertwined with the progress of monsoon over neighbouring India.

The advancement is also generally from east to west; it takes two days to reach the Kathmandu valley and five days to cover the whole country.

Early rains?

Last year, the monsoon entered eastern Nepal on June 20, delayed by 10 days against the normal date. This year, odd forecasts signal the onset likely earlier by a week over southwest coast of India.

The summer monsoon is responsible for 60- to 90 per cent of the rainfall recorded annually in the kingdom. The onset takes place in the eastern parts of the kingdom, and for this reason, the monsoon activity is more in the east rather than in the west.

Meanwhile, the US Climate Prediction Centre has forecast rain and thunderstorms for both northeast India and adjoining Nepal during the week ending May 3.

The week that follows could see the rain spread out to more parts of Nepal, especially to the west. North-East India and southern peninsula also could witness stormy weather and thundershowers.

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