Operations meeting in a wafer fab involves daily alignment of action items among key stakeholders: operations, maintenance, engineering and planning department. They have conflicting job functions. The maintenance department is required to conduct preventive maintenance (PM) to improve tools' reliability The engineering department is required to qualify new products and processes. Both cases interfere with the flow of production lots. The planning department must ensure production ramp up. This can have a short term impact on overall fab delivery and capacity. The primary challenge is to reach aligned decisions e.g. the best timing for PM or optimizing dispatch prioritization of production and development lots to ensure on-time delivery while maximizing capacity and tool utilization. In this paper we discuss the associated modelling issues of a 7-day simulation-based forecast, providing forecast of incoming WIP, moves and utilization at work center level. The simulation forecast consistently achieved an accuracy above 90%.