An appraisal of the Great Lakes advanced hydrologic prediction system

► AHPS forecasts capture seasonal and inter-annual Great Lakes water level dynamics. ► AHPS forecasts underestimate observed variability of Great Lakes water levels. ►Our findings provide a benchmark for future water level model testing. ► Our findings serve as a basis for identifying and prioritizing model improvements. ► Including a calibrated model error term in AHPS is a short-term research priority.