Rain can seriously affect the lift and drag characteristics of certain wing aerofoils.
Anything with a laminar flow wing may have degraded performance in rain.
Well... no certified airplane will be dramatically affected by rain on the wings. Certain amateur built designs are reputed to be more sensitive to airfoil contamination. If you're flying one of those types, you should be seeking specialist type wisdom.
Rain, in and of itself should not be a problem for VFR flight in a certified plane. However, visibility, possible thunderstorms, and the risk of icing in cold air really do need to be understood. Flying in near freezing temperatures, which may include needing to climb, or flying toward colder air, can take you into freezing conditions. The discussion of icing is it's own huge topic, and well worth either understanding thoroughly, or avoiding entirely.
Similarly, flying in snow must be well understood. In very cold air (> -10C), you're usually fine, as long as the visibility is adequate. Warmer than that, and again, you must be very careful, in that as the snow can begin to accumulate as airframe ice. Though I am hardly conversant in Canadian original languages, it has been said that the Inuit people of the far north have seven distinct words to describe snow. That sounds entirely appropriate to me! The fact that it's white and falling does not define what it's going to be like to fly through it! For those in locales where snow is less common, the differences in snow may elude understanding. Look down at the lawn - you see grass right? Look more carefully, how many different leaves and species can you distinguish? Similar with snow, and yes, you can have more than one type of snow at the same time.
So, when you're in snow at all, be more aware of it than just "the grass" of the lawn. Consider it's consistency, temperature, flake size, and stickiness. The consider the ambient air it's falling in. With those in mind, consider the affects of impacting it and aircraft skin which may be a different temperature than the air you're flying in. Experienced mentoring flying is the best way to get to learn snow. Next to that, is being hyper aware while you fly very locally in snow. If it starts to stick to the airframe, return the wisely short distance to home right away. The other thing is to know where on the airframe to first expect to see accumulation. On strut braced single Cessnas you'll see the snow accumulate first on the upper corner of the windshield, where it takes the shape of the leading edge of the wing. The fact that it is not accumulating on the center of the windshield does not mean that it's not accumulating dangerously on the leading edges of the wings!
The saying that good judgement comes from experience, and experience comes from using poor judgement really applies to flying in snow!