Electricity systems must expand and rapidly decarbonize while also withstanding extreme weather events that are becoming more frequent and severe due to climate change. Projecting the vulnerability and resilience of bulk electric power systems to both short- and long-term influences, from local to continental scales in the United States, requires new models tailored for explatory modeling (including high volume simulation under uncertainty).  However, a persistent challenge for power system modelers is striking an appropriate balance between model fidelity (e.g., scale and resolution) and computational tractability (e.g., wall clock run-time). This talk will discuss development of an open source power systems analysis tool designed explicitly to support MSD research. The tool, called GO (grid operations), was developed as part of the Integrated Multisector Multiscale Modeling (IM3) project. It is entirely open source and publicly available. GO allows users to customize quick instantiation of direct current optimal power flow (DC OPF) models for the three major electrical interconnections in the United States. Here, we detail how GO is used to build and and calibrate these models, and how these models can interact with weather and climate datasets to provide stationary and/or forward-looking assessments of physical grid reliability and market risk under a range of climate and technology futures.