Why is rain almost unknown in most of Antarctica?

Rain is almost unknown in most of Antarctica primarily because the continent is an extremely arid desert that receives very little precipitation of any kind.1

The scarcity of rain is due to several key factors:

• Low Atmospheric Moisture: The Antarctic atmosphere contains only about one-tenth of the water vapor concentration typically found in temperate latitudes.1
• Frigid Temperatures: Because of the continent's extreme cold, the limited precipitation that does occur falls almost exclusively as snow rather than rain.1
• Aridity: The inland polar plateau receives an average of only about 2 inches (50 mm) of precipitation per year (measured as liquid water equivalent), reinforcing its classification as a desert.1

While coastal areas receive more precipitation than the interior, the overall climate remains dominated by cold, dry conditions that prevent the formation of rain.1