When to Trim a Tree
Most shade trees are best pruned while they are dormant, and dead or broken limbs come off any time of year.
With the leaves down we can see every limb and how the tree is built, insects and disease are at their quietest around a fresh cut, and the wounds start closing as soon as the tree wakes up in spring. So late fall through winter is when we like to shape a tree, thin it or lift its crown.
A dead branch or a limb a storm has cracked does not wait for winter. It is a hazard now, and taking it off now does the tree no harm.