The skies above are always cold. For example, even in warm regions such as Okinawa, the temperature is low in the sky, and snowflakes form in the clouds over Okinawa.
However, the snowflakes formed in the Okinawan sky melt as soon as they fall and turn to rain. No matter how low the temperature of the sky in Okinawa is, it is still warm on the ground. Therefore, the snowflakes are completely melted by the time they fall to the ground.
Snow usually stays snow when the temperature is below zero degrees Celsius. At the very latest, the temperature limit is about 4 degrees Celsius. Therefore, snow only falls in winter when the temperature is low. In warm regions such as Okinawa, however, the temperature rarely drops to near zero degrees Celsius, even in the middle of winter. In such places, snow turns to rain as soon as it falls.