I visited Patnitop this weekend and it was a real fun vacation. It is around 3 hour drive from Jammu and the weather becomes pleasant only after you cross Udhampur. Until then, its not much different from the weather in Jammu or in delhi for that matter.
On way we halted for 30 minutes at Jhajar Kotli which is a river shore and many locals come there to enjoy playing in water. Its a very busy and famous picnic spot for many schools in Jammu and near by areas. After enjoying the fresh water of river tawi, we continued our journey, driving slowly and halting multiple times on road side to enjoy the scenic beauty of valley.