ALBUQUERQUE (KRQE) – During the overnight hours, cool air from the mountains sinks into the valley. This creates a cool, northerly flow at the surface. Meanwhile, the upper level winds are predominately southerly. The northerly surface wind allows the balloons to initially drift southward. Then, as the balloons encounter the southerly upper level winds, they begin to track back toward the north, passing the point of takeoff. As the balloon descends, they once again encounter the northerly surface winds allowing the balloon to return to the point of takeoff, thus creating a box shape during the course of the flight.