. Successes and Failures of Deterministic Quantitative Precipitation Forecasts leading up to the 2017 Oroville Dam Crisis

Abstract
During the period from February 2-11, 2017, the California coast was impacted by multiple atmospheric river events which contributed significantly to a record-breaking season of rainfall. Lake Oroville, already storing more than average amounts of water, experienced inflows of over 150,000 cfs during this period, however efforts to reduce the water level significantly were not begun until February 7, at which point the heaviest rainfall had begun to fall. Damage to the dam’s main spillway forced a reduction in release rates, which could not keep up with inflows, resulting in the use of the emergency spillway for the first time in the dam’s nearly 50 year existence. Erosion below both the damaged main spillway and the emergency spillway resulted in concerns of uncontrolled flows into the Feather River, and 180,000 residents downstream were evacuated as a precaution. An Independent Forensic Report found many issues with dam operations and maintenance that contributed to the crisis, but could underestimated or mis-located forecast precipitation also have been a factor? This study will examine deterministic precipitation forecasts for the upper Feather River and surrounding areas on decision-making timescales of a few days down to several hours using both global and regional forecast models. Questions to be addressed include: How did forecasts evolve in the days leading up to and early in the event? Did any forecast models produce the quantities of rainfall that were observed in the basin, and if so, were they correctly located? What about a given models’ treatment of the storm may have contributed to a successful or failed forecast? How may terrain interactions have affected the forecast? How might the forecast have changed with upgraded forecast models?