This research investigates the dynamics of GCs through very high-resolution idealized Weather Research and Forecasting (WRF) simulations: first under stability and shear conditions representative of the 14-15 February 2010 cyclone, then under modified radiative forcing, and idealized shear and stability profiles. This talk will discuss the development, maintenance, and structure of GCs (or lack thereof) under a wide range of upper-tropospheric conditions in the context of PLOWS observations. Under initially unstable conditions at cloud-top, GCs develop regardless of radiative forcing, but only persist clearly with radiative forcing. Cloud-top destabilization due to longwave cooling leads to development of GCs even under initially neutral and stable conditions, providing a physical explanation for the observed ubiquity of GCs atop winter cyclones. GCs do not develop in initially stable simulations with no radiative forcing. Decreased range in vertical velocity spectra under daytime radiative forcing is consistent with offset of the destabilizing influence of longwave cooling by shortwave heating.