If a lower cloud passes under a rain cloud when it is raining, will it block the rain, or will the rain fall through the lower cloud? I have often wondered about this.
—AJ Rubin, Highland Park
All precipitation (rain, snow, sleet, etc.) will continue down through the lower cloud. Clouds are composed of water droplets (or ice crystals, if the temperature is very low) and they present absolutely no barrier to rain drops or snowflakes. The relative humidity in a cloud composed of liquid water droplets is very high, generally at or near 100 percent. Rain drops will fall through such clouds and may actually grow larger if they pick up water droplets from the cloud through which they are falling.