Understanding the difference between graupel and sleet: A closer look

When we talk about graupel, a lot of people get  confused with sleet, but there's two different processes that are very similar on how each form. When we talk about sleet, we typically see the freezing temperatures that's going to create snow in the clouds and fall. Then, above freezing portions in the atmosphere will melt the snow into rain and eventually freeze before it hits the surface.

Graupel forms a tad bit different. There is going to be snowflakes starting in the cloud. As you get a little bit lower down into cloud,  there's going to be an even smaller above freezing region. What happens is we will have those snowflakes and ice crystals that are frozen that start to collide with water that's going to be super cooled. This super-cooled water starts to get on the edges of these little snowflakes and ice crystals and starts a process called rimming where it grows off of that encompassing the original snowflake with ice. 

Basically, similar to a snowflake but with a little bit of ice on the outside that continues to fall back down to the surface. This leads to those white balls.

There's a little bit of a difference in to what you should be looking at to tell how we can differentiate between gravel and sleet.  Oftentimes, sleet will look like tiny, transparent ice balls when seen and can take longer to melt than gravel.  

Graupel, on the other hand, is more of a white color and falls apart, melting quicker due to the rimming process.