Abstract: A rain guard and wind deflector device employs a flat panel of transparent plastic material installed by its mounting edge and adjoining opposing linear sides to corresponding linear sides of a window frame or window trim. The flat panel has a width to its free end extending over a substantial portion of the width of a window pane slidable on an inner track for opening the window. The flat panel leaves a small gap distance from the typical window screen in an outer track space of the window frame to allow air ventilation under rainy or windy conditions, while deterring dampness or dust passing into the interior of the house. A preferred plastic material is polymethyl methacrylate (PMMA). The flat panel can be preformed in standard sizes or cut to size and installed directly on the window frame or window trim without special tools and using common types of fasteners.