As an important index to measure the reliability of interchange power trading, available transfer capability (ATC) has been widely employed and investigated in existing studies and projects. With the rapid development of energy storage (ES) technology, ES can take advantage of responsive capability to flexibly shift peak load to valley hours, thus effectively enhancing regional ATC. However, the impacts of ES on ATC have not yet been systematically explored. To fill this gap, we evaluate the contributions of energy storage to ATC enhancement in this paper. A two-stage ATC evaluation framework is developed considering the load shifting capability of ES. In the first stage, a day-ahead unit commitment model is formulated to schedule generators and ES. Scenario-based stochastic programming is adopted to depict the uncertainty in renewable power and load. In the second stage, a real-time ATC model is used to quantify the maximal capacity of further interchange power trading. Case studies based on IEEE 14-bus system demonstrate the impacts of ES on enhancing realtime ATC while facilitating renewable energy accommodation.