Patna: A small weather system in the form of a cyclonic circulation in the Himalayan Bengal and a trough line starting from north-eastern Uttar Pradesh and passing through the centre of Bihar have not allowed the mercury level to cross 40°C till now this summer.

In fact, under the impact of the twin weather phenomena, some parts of north Bihar may also witness thunderstorms.

Earlier, the Patna Met office had hinted that weather in most parts of the state would remain clear and the temperature level was likely to cross the 40°C mark this week and westerly was likely to be the dominant wind during most part of the week. Thankfully, however, the weather didn't follow the script. The easterly became the dominant wind from Monday, not allowing the mercury to soar much.

On Tuesday morning, a few patches of clouds were also visible and a few places in eastern Bihar received some rain. Patna Met office meteorologist Sandeep Kumar attributed the prevailing weather condition in Bihar to a small weather system prevailing in the Himalayan region in Bengal, and the positioning of the trough line.

"Under the impact of these factors, easterly wind is blowing in most parts of the state and some places in eastern Bihar including Purnea, which is nearer to Bengal, also received some light rainfall. Also, due to passage of the trough line through the state, one or two places in north Bihar may witness thunderstorm also," Sandeep said. Easterly winds generally lead to moisture incursion in the atmosphere. This moisture does not all allow clear passage of the sunrays to the Earth's surface and hence the temperature levels do not rise much. In case of westerlies being the dominant wind, the moisture level goes down, allowing free passage of sunrays to the Earth's surface which leads to increase in the day temperature.

Speaking about the likely temperature conditions in coming few days, the meteorologist said that the easterly was likely to prevail in most part of the state till April 21 and hence the day temperature was not likely to cross 40°C in north and eastern parts of the state.

He, however, added that westerly was likely to become dominant wind April 22 onwards, after which the day temperature would increase.