The main source of winter rain in these states (excluding that of South India) is a western disturbance (or an upper air trough). The location and amount of rainfall in the plains depend on the location and strength of these western disturbances. If they strike Jammu and Kashmir and are weak, then this will produce a localised effect i.e North and Central India's plains won’t get any significant impact. But if they strike in lower latitudes and are strong, then the plains receive widespread impact in terms of rain and cloud cover.
As till date, we have been witnessing sluggish western disturbances, it was being doubted whether India will receive any widespread rain event in this winter. This rain is very beneficial for winter crops (provided it occurs at the right time). So after a long waiting period, many states of India will witness the first rainfall of this year starting from Sunday, January 17 2016 till Friday, January 22, 2016.