With snow and sleet in the forecast for this week, let's take a close look at why both types of wintry precipitation occur.  Firstly, ice develops when temperatures are at 32 degrees or lower. These temperatures are deemed as freezing, but in this scenario, we will call it cold air. Conversely, anything above 32 degrees Fahrenheit we will call warm air. 

Whenever there is snow,  the column of air usually contain temperatures that are 32 degrees or lower. Sleet is a little more complicated, as there is a cold layer aloft, a warm layer in the middle and a larger cold layer at the bottom. In the cold layer aloft, only snowflakes exist because the air temperature is at or below freezing. The snowflakes then partially melt in the middle warm layer due to temperatures above freezing . The partially melted flakes refreeze into ice in the larger cold layer beneath (forming sleet).