I like to elaborate JudyB' s statement for whoever is new to this hobby. If the new growth comes out when it is cold, the cold temperature will kill the young tender parts of the tree. It means the tree unnecessarily lost its energy and this situation may lead to the tree's death.
The plants will go into winter dormancy when air temperature goes down less than 50 degrees F in about 7 days and the day length is shorter. The parts of the plant above the ground will go to sleep but the root system is still awake during dormancy. Prior to pruning in the end of the Summer, one must make sure that the new growth will not push out in Fall or winter after pruning. I always closely follow the prior 2 week- weather broadcast to decide which work I can do on the tree such as pruning, transplanting. When I see the nighttime temp. has been constantly below 50 degrees F, it is the time to perform those work on my trees.
Bonhe