Reliable Grid Forecasting: State Space Models for Safety-Critical Energy Systems

Accurate grid load forecasting is safety-critical: under-predictions risk supply shortfalls, while symmetric error metrics mask this operational asymmetry. We introduce a grid-specific evaluation framework (Asymmetric MAPE, Under-Prediction Rate, and Reserve Margin) that directly measures operational risk rather than statistical accuracy alone. Using this framework, we conduct a systematic evaluation of Mamba-based State Space Models for California grid forecasting on a weather-aligned CA ISO-TAC dataset spanning Nov 2023 to Nov 2025 (84,498 hourly records across 5 transmission areas). Our analysis reveals that standard accuracy metrics are poor proxies for operational safety: models with identical MAPE can require vastly different reserve margins. We demonstrate that forecast errors are weakly but statistically significantly associated with temperature (r = 0.16), motivating weather-aware modeling rather than loss function modification alone. The S-Mamba model achieves the lowest 99.5th-percentile reserve margin (14.12 percent) compared to 16.66 percent for iTransformer, demonstrating superior forecast reliability under a 99.5th-percentile tail-risk reserve proxy.