India is a vast country, stretching from 8N way up to 35N. And there can be huge variations in climate and weather in such a difference in latitude. As well as the geographical topography differs all along the length of the country.
When does Summer begin for our region? On the basis of previous years' behaviour of the rising temperatures, and from past records and observations, i would consider 1st March as the start of the Summer season for the entire stretch of India, barring the Northern States of Kashmir, H.P. Utterakhand, and the NE states , east of Bangladesh.
These exempted states have a prolonged winter, by 15 days, before they too fall prey to the blazing sub-continent sun.
And, normally, the behaviour of the rising temperatures, that is the "route" summer would take is from the South towards the North.
Too early ? You think 1st March is an early assumption of Summer arrival date ?
Well, look at this image of the not to distant future !
1st March 2009, and the 41s are into sindh (Pakistan).
And for the Northward movement of Summer, check this image of 14th. March 2008. 47c in Sindh !
Last year, 2010 March, was hot from the start itself. Reason: A high pressure ridge at 500 mb had established itself over the Sindh/Gujarat region in early March itself. This ridge moved east and plonked over NW India.
This prevented the westerlies, and the jet streams, associated with the W.Ds from coming and precipitating over the sub-continent. Instead the W.D.s and cold fronts were pushed up further North into Central Asia last year.
Well, we have exceptional years like this image too ! March 14th. 2007.
March 2011 has F5 transversing across the Northern States of the sub-continent till the 5th. of March. So week 1 is ok and cool. As of now, week 2 has no W.D. coming up to keep things cool. But M1 is a possibility around 10th.March. But we will wait and watch for the developments.
I see temperatures rising after 8th. March in the Northern regions. But central regions will see rising temperatures by about 2c in the 1st week itself.