Image Credit: weather.gov
Image Credit: weather.gov
Image Credit: weather.gov

It’s getting to be that time of year again where more than just rain can fall from the sky in Georgia. This edition of Meteorology 101 will break down the differences between rain, freezing rain, sleet, hail, and snow, so you can be ready for whatever “Old Man Winter” throws our way in the upcoming months. Precipitation. What is it? Well, precipitation is any liquid or solid water particle that falls from the atmosphere and reaches the ground. Before we talk about these types of precipitation, we have to start with some basics.

The Atmosphere:

Earth’s atmosphere is broken down into various layers: the troposphere, the stratosphere, the mesosphere, and the thermosphere. The troposphere is the lowest layer of Earth’s atmosphere, and it is in this layer that we live in. The vast majority of weather also occurs in this layer. In the troposphere, temperature decreases with height, though there are exceptions, which we’ll see later on in the post. The other layers of the atmosphere are important too, but for the purposes of this post, the troposphere is key.

The layers of the atmosphere. Notice the decrease in temperature in the troposphere? Image Credit: theozonehole.com
The layers of the atmosphere. Notice the decrease in temperature in the troposphere? Image Credit: theozonehole.com

Rain:

We’ll begin our exploration of precipitation types by talking about the most common form of precipitation we see in Georgia: rain. Why is rain the most common precipitation type we see? Initially, at the height where clouds form and rain begins to fall, temperatures can be below freezing. As these droplets or ice crystals fall they encounter a layer of the troposphere where the temperature is above freezing, and any ice crystals will melt. If the layer of above freezing temperatures extends all the way to the ground, as is common in Georgia for most of the year, rain will be the resulting precipitation type. When this layer of the atmosphere isn’t above freezing all the way to surface, things begin to change.

Fun Fact: Rain drops are not teardrop shaped! Rain drops begin their journey through the atmosphere as round droplets, but as they fall, they lose their round shape as they collide and coalesce with other droplets. Instead, they look more like a hamburger bun.

No teardrops here! Only hamburger buns! Image Credit: NASA.
No teardrops here! Only hamburger buns! Image Credit: NASA.

Freezing Rain:

Perhaps the most debilitating precipitation type, freezing rain can rear its ugly face quite frequently in North Georgia during the winter months. All it takes it the right synoptic (big picture) set up along the eastern seaboard, and freezing rain can become a definite possibility. When Athens experiences a cold air damming event in the winter, and precipitation is present, freezing rain, along with sleet, can be a likely precipitation type.

The difference between rain and freezing rain is the area of the atmosphere right above the ground. If this area is at or below freezing, rain will freeze upon contact, creating slippery roadways and sidewalks as well as weighing down trees and power lines. The area of the atmosphere just above the surface that is above freezing is what meteorologists call a temperature inversion. A temperature inversion is present when the temperature increases with height. Since the surface is at or below 32°F when the rain falls, the air above the surface needs to be above freezing so that the precipitation falls as just rain. When Athens experiences an Ice Storm, freezing rain is the culprit.

Temperature profile for freezing rain. Image Credit: NOAA (annotations by me).
Temperature profile for freezing rain. Image Credit: NOAA (annotations by me).
Extreme case of freezing rain weighing down power lines! Image Credit: atmosdu.com
Extreme case of freezing rain weighing down power lines! Image Credit: atmosdu.com

Sleet vs. Hail: 

The confusion between sleet and hail from the general public is one of a meteorologist’s biggest pet peeves. The confusion is understandable. Both sleet and hail are made up of ice, and both can make the ground turn white for a brief period of time. But that’s where the similarities end.

We’ll start by talking about sleet. Sleet occurs during cold season months. You can think of it this away: sleet and snow both start with an “s,” and they’re both wintry precipitation. Sleet formation is very similar to freezing rain formation. The key difference is that the cold layer near the surface is deeper, so instead of rain hitting the surface and freezing, the raindrops have time to refreeze and form little balls or pellets of ice.

Now for hail. Hail is not a wintry form of precipitation. It occurs in thunderstorms as supercooled water droplets are forced to ascend upward through the cumulonimbus cloud by a powerful updraft. As the forming hailstones pass through differing layers of water droplets, it begins to grow in size. Eventually, a hailstone becomes heavy enough where the updraft cannot keep it inside the storm any longer. It then begins its decent down to the surface.  Hail can be as tiny as a dime, which could be the reason it gets confused with sleet. Here’s one of my favorite hail videos:

Snow:

Our final precipitation type is snow! Everyone knows what snow is, even those of us here in the South. Snow occurs when the entire atmospheric column, from cloud all the way to the surface, is below freezing. The surface doesn’t always have to be at or below freezing for snow to fall, but accumulation is more likely if the surface temperature is at or below freezing. This is the reason snow is so rare here in Georgia. It takes all the right pieces coming together for the atmosphere here to support snow.

Did you know: The temperature and humidity of the atmospheric column determines what shape the snowflakes will take.

The temperature of the atmospheric column determines the snowflake's shape. Image Credit: www.its.caltech.edu
The temperature of the atmospheric column determines the snowflake’s shape. Image Credit: www.its.caltech.edu

Snow can either be wet or dry. Dry snow is not the kind of snow you want if you enjoy making snowmen and having snowball fights, as it has a lower density. Dry snow is associated with dendrites and scattered plate snowflake shapes. Wet snow is usually the kind of snow we see in Georgia because it’s usually only around freezing when snow is falling. A good rule of thumb is that 1 inch of rain equals 10 inches of snow. Though, this rule of thumb changes once you take into account the available moisture and temperature in the atmosphere.

Here’s a snow video from the March 1st, 2009, snowstorm in Athens, Georgia. The snow in this storm was very wet and caused some minor roof collapses as well as some sagging tree branches. Do you remember this storm?

Putting It All Together:

After reading this post, I hope you have a better understanding of precipitation types, especially how they form and what makes them different from one another. Rain vs. freezing rain and sleet vs. hail are important types of precipitation to be able to tell apart as they each pose their own risks. Most importantly, I hope this comes in handy as we approach the winter months, and I hope this post helps you differentiate what you see falling from the Georgia sky!

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