The devastating thunder-squall of Tuesday night had signs of a tornado.

In a latest finding, the weather observatory at the Chunapur airbase at Purnea - the worst-hit district - recorded the average wind speed during the thunder-squall at around 180kmph. Such extremely high wind speed has caught the attention of senior officials in India Meteorological Department (IMD), which does not have its observatory in Purnea.

Ashish Sen, director at Patna meteorological centre, claimed that a storm having a wind speed of 140km per hour and above qualifies to be a tornado-like weather phenomenon. But it has to meet several other criteria for officially being declared a tornado.

"There is not much difference between a severe thunder-squall and a tornado. Once the wind speed under a thunder-squall goes above 140kmph at the ground level, we look into the possibility of it being a tornado," said Sen.

A senior official in the Indian Air Force at the Chunapur airbase told The Telegraph on Friday afternoon that a maximum of 180kmph of wind speed was recorded at their observatory at the time of the thunder-squall.

One of the criteria of tornado listed by the Met chief is uprooting of huge trees like peepal and banyan, followed by their vertical lifting by the high speed wind and falling a few feet away from their original location in the end. A hole also needs to be formed in the ground from where it is uprooted.

While moving in the rural as well as urban areas in Purnea, The Telegraph did spot a number of gigantic banyan and peepal trees completely uprooted. They were lying on the streets. The uprooting of the trees did lead to formation of hole at the place of their root but it could not be assessed clearly whether they have fallen several feet away from their original location.

The severe impact of the high-speed wind was also visible in the form of broken stem of strong banyan and peepal trees at a number of places.

Another criterion listed for a thunder-squall being declared a tornado is the feeling of a sudden and momentary heat before it reaches its peak. Many residents of Kohilwa panchayat in Dagarwa block in Purnea accepted that they felt sudden heat during the devastating squall.

"It felt suddenly very hot immediately before and after the squall. In fact, it felt like aag ka gola (fireballs) were falling from the skies," said Shyam Kumar Mandal, a resident of Kohilwa panchayat.

Though several conditions for satisfying the norms for being tornado are being found in the case of the thunder-squall on April 21 night but weathermen claimed that it did not seem to satisfy the criteria of vertical lifting of objects.

"If there would have been a case of vertical lifting as well, the uprooted trees would have fallen a few feet away from their original location. The asbestos and metallic sheds would have been found hanging on trees. But we could not find any substantial evidence of such incidents, thus we are still not confirming it to be a tornado," said Sen.

The disaster management department report on storm put the number of affected families at 71,123 in different districts. The report said a total of 224 panchayats in 43 blocks have been hit by the high speed storm.

It said 51 animals perished in the storm and the maximum, 50, are in worst-hit Purnea. A total of 69,773 dwellings have been ravaged either totally or partially, the report said. Most of them - 41,350 - are in Purnea while 16,624 are in neighbouring Katihar district, the report said.