Improving Atmospheric River Forecasts ActThis bill requires the National Oceanic and Atmospheric Administration (NOAA) to establish an atmospheric river forecast improvement program.In carrying out the program, NOAA must seek to reduce loss of life and property and other economic losses caused by atmospheric river events through research and development on accurate, effective, and actionable forecasting and warnings. The program must generally involve the establishment of quantitative atmospheric river forecast skill metrics, the development of an atmospheric river forecast system within a unified forecast system, and the development of tools and products to predict periods of active or inactive atmospheric river landfalls and inland penetration, among other activities. The program must periodically test and evaluate the value of incorporating innovative observations (e.g., observations from radar, aircraft, ocean buoys, and other sources) to facilitate the improvement of modeling and forecasting. The program must also consider the development of best practices for communicating the existence and severity of atmospheric river events, as well as other information about atmospheric rivers. The program may seek to improve precipitation modeling, with an emphasis on forecasting for complex terrain. The bill also requires NOAA to acquire and sustain adequate crewed and uncrewed aircraft (i.e., drones), equipment, and personnel necessary to meet air reconnaissance mission requirements annually during the expected atmospheric river season (November through March).