Whoa - that's a really nice trip with interesting options.
There are direct flights, trains and buses for this journey. New Delhi (Delhi) to Jammu (Jammu And Kashmir) distance is 583 km and you can get there by flight in just over 1 hour and 10 minutes or by train fares starting from ₹ 162.
The weather at Jammu is varying from "nice" to "hotter than nice".