You might be surprised to learn that sunny cold weather is actually an ideal condition for solar panels to perform optimally. On the other hand, extremely hot climates actually make solar panels less efficient.
As far as snow is concerned, a light dusting of snow has little impact on the panels and can be easily blown off by wind. Because panels are tilted at an angle, snow will also slide off of panels over time, cleaning the panel as it melts and slides off. After heavier snowfalls panels will be cleared by facility employees. Interestingly enough, because of the reflectivity, or albedo effect, of snow, having snow on the ground near the panels can contribute towards them producing more electricity, with the smooth white surface reflecting light like a mirror.