Mercury set to scorch North

 "Towards the end of next week, temperature is likely to rise to 43-45 degrees Celsius. The condition may stay for 7-10 days," Ajit Tyagi, director general of the Indian Meteorological Department told Deccan Herald.

While Delhi struggled under the smouldering 44 degree Celsius on Sunday, the mercury continued to climb northwards with Agra registering 46 degree. Gwalior, Varanasi, Ahmedabad, Nagpur and Gaya sizzled just a degree shy with 45 degrees. Temperature remained between 41 and 43 degree Celsius in many of the north and north-eastern cities, five to six degrees above normal.

The north, including the national capital, can expect a drop in temperature on Monday and Tuesday due to a western disturbance which has already brought some rains over Jammu. But that is the only good news the region would have, as the searing heat is likely to return during the second half of the week due to weather patterns like "subsidence" or "blocking high", accentuated by the absence of western disturbances and a clear sky. Subsidence is seen in high-pressure areas where the air generally sinks or subside. As air falls it warms, preventing cloud formation. Blocking high happened when a high pressure zone stays in the same place for some days and create blocks for other weather systems. "Subsidence can happen over a large area and caused by downward movement of air. It can remain stagnant for days. A tropical cyclone can disturb such a system," said Tyagi.

Another factor contributing to the heat wave would be an "anti-cyclone movement", which also prevents cloud formation.  "Probability of April being warmer than normal in most parts of the country especially in the southern peninsula is very high," says an IMD analysis of the unusually warm March 2010.

Possibilities of thundershowers in April are also less this time round. Even though March is known as the summer-to-winter transition month, heat waves were seen in March itself. It was the second warmest March in Delhi since 1901.

As many as 21 meteorological sub-divisions out of 36 witnessed heat wave conditions in March which recorded 17 per cent heat wave incidents - the second highest after June.