Roll Clouds are frequent features of the arctic atmosphere near the ice-ocean margins where strong horizontal thermal gradients exist. Previous 2-D model work has shown that ice microphysics, and in particular, ice nuclei can significantly modulate roll cloud dynamics through modifications to the precipitation process. Our current work, which we will present at the meeting, extends our earlier studies using a 3-D LES model with explicit microphysics. We will present results that illustrate how microphysics alters roll cloud structure (such as wavelength, depth, etc.) and dynamics.