Improving Atmospheric River Forecasts Act This bill requires the National Oceanic and Atmospheric Administration (NOAA) to establish programs that support atmospheric river forecasts. Specifically, NOAA must establish at least one pilot program to support subseasonal and seasonal precipitation forecasts for water management in the western region of the United States, including improvements with respect to atmospheric river modeling. NOAA must also establish an atmospheric river forecast improvement program to reduce the loss of life and economic losses from atmospheric rivers. The program must evaluate the value of innovative observation methods, such as uncrewed aircrafts and other emerging technology.