Reducing bias in OAR’s Earth System Model is an indicator of the improved skill of precipitation simulation. Bias is defined as the long-term mean (or average over time) difference between a simulated (model generated) value and the observed value. This performance measure will track the reduction in bias (e.g., percent reduction of the current FY21 bias) in U.S. seasonal precipitation simulations in OAR Earth System models based on a percentage of bias in past Earth System models.