Weather Radar Coverage Improvement Act This bill requires the National Oceanic and Atmospheric Administration to develop a plan to replace the Next Generation Weather Radar (NEXRAD) system of the National Weather Service by September 30, 2040. The plan must incorporate certain elements, including estimates of improvements to coverage and accuracy and the potential use of commercial radars. The bill also authorizes the National Weather Service to contract with third parties to fill gaps in radar coverage so as to better detect significant weather events over a larger area.