An expandable grain tank is provided for covering the open end of a grain tank of an agricultural combine. The expandable tank includes a tarp and a support structure for raising and lowering the tarp. The support structure is configured with an upper frame, a plurality of expandable legs connected to the upper frame and the grain tank, and an actuator to expand and retract the expandable legs. The expandable tank is configured to be moved between a retracted position and an expanded position.