1.   Elsewhere, a thin warm layer aloft melted the flakes, but the drops refroze into pellets of ice called sleet.

2.   Sometimes a warm layer aloft will melt the snowflake before reaching the ground.

3.   Sometimes a thick warm layer aloft will melt the snowflake into a drop of rain before reaching the ground.

4.   The top layer solidifies before the bottom layer melts.

5.   Transportation is even more difficult after the top layer of permafrost melts in May.