We revisit the computation of a "snow line'' in a passive protoplanetary disk during the stage of planetesimal formation. We examine how shadowing and illumination in the vicinity of a planet affects where in the disk ice can form, making use of our method for calculating radiative transfer on disk perturbations with some improvements on the model. We adopt a model for the unperturbed disk structure that is more consistent with observations and use opacities for reprocessed dust instead of interstellar medium dust. We use the improved disk model to calculate the temperature variation for a range of planet masses and distances and find that planets at the gap-opening threshold can induce temperature variations of up to +/- 30%. Temperature variations this significant may have ramifications for planetary accretion rates and migration rates. We discuss in particular the effect of temperature variations near the sublimation point of water, since the formation of ice can enhance the accretion rate of disk material onto a planet. Shadowing effects can cool the disk enough that ice will form closer to the star than previously expected, effectively moving the snow line inward.
