arXiv:2611.14439v1 Announce Type: new Abstract: This paper presents a cascading contingency analysis and risk assessment framework that incorporates probabilistic mode transitions motivated by stochastic hybrid system (SHS) concepts together with power-flow-based stress evaluation. A two-stage modeling approach is adopted in which sensitivity-based analysis is first used to identify candidate cascading transitions, followed by DC power flow re-evaluation to accurately capture post-contingency stress redistribution, islanding behavior, and load shedding. A probabilistic propagation model is constructed using mode-dependent transition probabilities derived from line loading conditions. A Cascading Risk Index (CRI) is introduced to quantify the expected load shedding accumulated over cascade progression. Case studies on the IEEE 39-bus system demonstrate that the proposed framework captures diverse cascading routes under multiple initiating outages and identifies critical propagation patterns that are not revealed by N-1/N-2 screening. The results highlight the importance of SHS modeling in assessing cascading risk and providing a scalable framework for resilience evaluation in modern power systems.