Flying Below The Clouds
Temperatures between 0 degrees and -5 degrees Celsius are most prone for water and wet snow combinations in the air. Snow gains mass much faster than small liquid droplets, and subsequently precipitates out of the cloud first. If liquid droplets remain suspended in the cloud, you probably won't encounter much risk for ice. However, if the liquid does begin to precipitate and the temperatures are around 0 to -5 degrees, you're putting yourself at risk for accumulating substantial ice. In this case, the colder the air temperature below 0, the safer you'll be.
But don't let the dry snow below the clouds fool you. There could still be plenty of super-cooled liquid within the cloud itself, which is the perfect recipe for icing conditions. If the water droplets in the cloud gain enough mass to precipitate before they fully freeze, you might run into freezing drizzle or rain, which is the worst case scenario you could find yourself in.
Flying Through Clouds With Snow
If you fly through a cloud with snow in it, you'll likely be flying in icing conditions unless temperatures are well below -20 degrees Celsius. Snow forms from moisture accumulating and sticking together, so if you fly through that formation process you're likely to encounter liquid that will turn to ice on your airplane. Don't expect to find just dry snow inside a cloud.
