Thunderstorms seen lining up over North-West and South

Parts of north-west, north-east and southern India will experience rain or thunderstorms intermittently during the next two weeks.

Two back-to-back western disturbances blowing in cooler air from across the Indo-Pakistan border will be the trigger for regionally violent weather.

‘Trough’ present The cool air will prevail over land that is just to beginning to warm up. The land-air contrast will set up the background for pyrotechnics in the atmosphere manifesting as localised high winds, thunderstorms and rain.

An India Met Department update on Wednesday said that a ‘trough of lower pressure’ in the atmosphere is already extending from Odisha to south Tamil Nadu.

Atmospheric troughs represent narrow corridors which feature winds charge in from opposite directions to set up instability.

Troughs forming during this time of year are breeding grounds for thunderstorms which line up along its length from north to south. In this manner, they also announce the setting in of the pre-monsoon season.

The Met Department sees the trough persisting in intensity for the next coupe of days. But international models indicate that the formation could be in for a longer haul.

Long haul In fact, there is a second trough, though smaller in size, over eastern India linking Assam and neighbourhood with Gangetic West Bengal.

This trough is expected to be even more intense thanks to moist south-westerly winds from adjoining Bay of Bengal blowing in straight into it.

The Met Department expects that a follow-up western disturbance will roll into the northwest India by the weekend. It will only help perpetuate the thunderstorm regime in the region.

The Met said that minimum (night) temperatures stayed below normal by 2 to 5 deg Celsius overnight in many parts of northwest and central India in what is seen as an indicator of the extended winter.

Harsh in south At the same time, day temperatures have begun to look up elsewhere, especially in the South, which signals how the summer is catching up in earnest.

International models had indicated earlier that north and north-west India are likely to stay cooler than normal during April/May. Harsher summer conditions are expected in peninsular India.

This pattern is one factor that could affect the strength of the South West monsoon since heating of north-west India is a crucial enabler for rain-bearing winds to blow in from the south-west (Kerala coast).

Heating causes the air over land to lift and pressure to reduce. This in turn guides monsoon winds from the south-west to fan into the farming heartland of north-west India.

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