Wind-tunnel tests were conducted using a 30%-scale DrivAer model, in estateback and notchback rear-geometry configurations, to investigate aerodynamic performance changes associated with snow and ice buildup on passenger vehicles. Around 20 snow/ice accumulation patterns were tested, at a Reynolds number of 2.8 million based on model wheelbase, for each of the notchback and estateback variants. 5 additional patterns were tested on the estateback with roof-rack support bars. Snow accumulation was modelled with foam, while ice accumulation was simulated with aluminum tape hand-formed to the desired shape. A simulated full-scale snow thickness of 58 mm on the hood, roof and trunk increased the wind-averaged drag coefficient by 16% for both model variants. With 90 mm of snow, the drag of the estateback variant increased by 19%. Drag changes increased with, but were not proportional to, snow thickness. Chamfered front and rear edges, representing windblown shapes, reduced the drag penalty compared to square-edged snow models. The largest drag increases, of 18% and 20%, respectively, for the notchback and estateback configurations, were due to simulated patchy snow and ice on multiple surfaces. Localized ice/snow patches sometimes caused stronger increases in drag than a similar or larger volume of precipitation elsewhere. Critical surfaces include the A and aft-most (C/D) pillars, the lower-front corners, the leading-edge of the hood and the leading- and trailing-edges of the roof. Simulated snow and ice at more upstream positions often caused higher increases in drag than accumulations further downstream. Drag and base pressure were more likely to be correlated for changes closer to the rear of the model. Some snow/ice patterns were found to increase side force and rolling moment in crosswinds, or to increase lift and change the pitching moment, potentially affecting vehicle stability and traction. The results are intended to support additional studies that will examine the impacts of snow/ice accumulation on fuel/energy use and safety.