Complex sentence: On 21 November, a cold front left the east coast of the United States, and slowly moved eastward, then stalled midway between Bermuda and the Azores Islands on 25 November.
Split into simpler sentences: On 21 November, a cold front left the east coast of the United States, and slowly moved eastward. It then stalled midway between Bermuda and the Azores Islands on 25 November.