Write an expense forecast model specification in a {{tone}} tone for {{target_audience}} in the {{industry}} sector, with purpose {{model_purpose}}. Cover model overview, input assumptions, 3-tab structure (Assumptions & Inputs, Expense Forecast Core, Output Dashboard), scenario analysis (Base/Bull/Bear), sensitivity tables, and quality checks. Keep under 1800 words. Use Excel-compatible formulas. Skip any section if information is unknown. Paste any relevant background information after these instructions before running.