“… a similar but lesser effect from rain”, re de-icing fluid.
IIRC some old studies of the effects of de-icing fluid on lift and drag concluded that any deterioration was minor. However more recently, several manufacturers evaluated the new higher-viscosity de-icing fluids, which depending on aircraft type showed some deterioration or the need to adjust configuration / speeds to maintain controllability standards.
Rain, in comparison with de-icing fluid, has relatively low viscosity and thus might not be such a problem.