Difference Between Snow, Sleet, and Freezing Rain
Posted Wednesday, Dec 12, 2018
I don’t know about you, but sometimes the forecast intrigues me. Why do we get snow in cold weather occasionally, but other times, under seemingly the same conditions, we get sleet? And, under what seems to be the same conditions, we get freezing rain? And, isn’t sleet frozen rain? So, what’s freezing rain? The difference between snow, sleet, and freezing rain arises from how or where the freezing takes place.
Snow. Snowflakes form when water in the upper sections of clouds begins to freeze. Interestingly, these droplets freeze in a crystalline pattern always having six arms. As the flakes fall through more moisture, they continue to grow. Since each flake follows a unique path to the ground, no two flakes grow in the exact same way, so no two snowflakes are identical. If the atmosphere is below freezing from the bottom of the cloud to the ground, the precipitation remains in this crystalline-flake form and we get snow.
Sleet. Sometimes snowflakes fall through a layer of air that’s above freezing during their trip to earth. Obviously, they begin to melt. If the next layer is once again below freezing and is deep enough, the partially melted drops refreeze, but not in a crystalline pattern. This time they freeze into small, almost spherical shapes. We call this sleet.
Freezing Rain. If the snowflakes melt in a warm layer and then enter a layer that is below freezing but shallow, the droplets do not have time to refreeze; however, they become super-cooled (barely above 32 degrees). In this state, they will instantly refreeze the moment they come into contact with an object that is 32 degrees or below, i.e., the ground, tree limb, or power line. In this way, they form a layer of ice. We refer to this phenomenon as freezing rain.
You may have noticed that all three of these types of precipitation began as snowflakes, which is associated with winter weather. But what about hail that occurs in the summer?
Hail. Although it may be warm/hot at ground level during the summer, the upper levels of storms can be extremely cold. Sometimes when a storm has an updraft, it can lift raindrops upward into these areas where the drops freeze and begin to fall. If the updraft is strong enough, these frozen drops will be lifted back through the super-cooled moisture in the cloud where they gain another layer of ice. This cycle can occur several times, and each time the frozen drops increase in size until they are too heavy for the updraft to lift again. Then, they fall to the earth as hailstones.
So the next time the meteorologist gives a forecast for various precipitation, we’ll all be clear on the difference between snow, sleet, and freezing rain and how they form. Now, why in the world are they called meteorologists? Would meteors really be considered precipitation...
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