Flower buds are some of the least cold-hardy parts of the tree. The low winter temperatures might have been enough to damage the flower buds but not the leaf buds and other vegetative parts of the plant. In this case the plant will leaf out normally but will not bloom. Sparsity of bees can reduce the crop, although some fruit should set by self pollination. Plant a tree of a different cultivar of apple within 40 feet of your tree.
Crabapples also make good sources of pollen.
Frost during the bloom period, or very cold weather just before bloom can damage the flowers and prevent them from setting fruit. Rain or damp weather during bloom can reduce bee activity. It can also make the pollen grains clump together and make it difficult for bees to carry them. Low relative humidity and drying winds can damage the style and stigma of the flower and prevent fertilization. Bees don't fly effectively in windy weather.