Although sleet and hail are forms of ice precipitation, they form in very different ways and often at different times of the year. While hail usually falls in the summer or during the warm season, other hard precipitation falls in the winter – sleet.
Sleet and hail are different because of their freezing method. Sleet is formed when snow and rain mix and fall to the earth. Hail is formed when rain is pushed farther upward by thunderstorm updrafts and freezes. This is why sleet has a slush-like texture, while hail is harder.
Wet rain is formed during winter storms, while hail is a form of precipitation during warm weather. Wet snow forms in winter when raindrops freeze on their way to the ground.
Wet rain freezes again as it passes through the deep frozen air above the surface, eventually reaching the ground as icy raindrops bounce off impact. As the frozen water droplets pass through the lower atmosphere where the air is warmer, they dissolve into droplets and fall to the ground as rain.
The Difference Is in the Icing Method
The key difference is that icing occurs when rainwater passes through frozen air, causing it to freeze before it reaches the ground. Because the precipitation falls into the cold air, the snow does not melt on the way down, but reaches the ground like snow. Freezing rain falls in the form of snow that, like wet snow, melts in the warm air.
Precipitation starts as snow in the cold layer above, then melts into rain as it passes through the warm layer, and then refreezes into sleet or freezing rain as it passes through the cold layer near the surface.
As noted above, sleet forms when snow melts into a warm layer and then refreezes into ice balls as it falls through a cold layer. As this snow falls through the warmer layer of the atmosphere, it melts a little and then turns into a ball of ice as it falls through the colder region, causing it to fall to Earth as sleet. At ground level, sleet only occurs during winter storms when the snow melts during the fall and the resulting water refreezes into sleet before hitting the ground.
Sleet Is more Similar to Snow
Depending on the intensity and duration, sleet can accumulate on the ground in the same way as snow. Since the droplets do not jump up and down in a cloud, sleet cannot grow to the size of a hail and usually reaches the ground in the form of small ice balls. Before reaching the Earth’s surface, sleet must pass through another layer of subzero air, where it will freeze again and turn into ice balls.
This happens when the clouds are cold enough to snow, but the layer of air above the ground is above freezing. Wet rain occurs when snowflakes only partially melt as they pass through a layer of warm air on the ground. If snowflakes fall into the atmosphere without passing through a layer of air that is warmer than freezing, the snowflakes will continue to fall to the ground without melting. When the ground temperature drops below 32 degrees Fahrenheit, the clouds begin to fall like snow.
All forms of precipitation (water from the atmosphere falling to the ground) start as snow in the clouds. Hail is all forms of precipitation starting with snow. Graupel is a bit like snow, a bit like sleet, a bit like hail.
Freezing Method Determines Precipitation Type
Depending on the path of ice precipitation through the atmosphere, it can be snow, hail, or even sleet or freezing rain. Precipitation can be in the form of liquid water (rain and drizzle), liquid water that freezes on contact with the surface (freezing rain or drizzle), or frozen water (snow, ice needles, hail and sleet).
Other solid precipitation is smaller than hail and forms when clouds are warmer than the air below and there is little updraft. Sleet is not as dangerous as freezing rain because it doesn’t freeze on contact, but instead bounces off the ground and builds up (if you hear snow, it’s sleet!). Freezing rain is real and looks a lot like sleet or fine hail, but these balls are made of snow instead of ice and are white.
Three Precipitation Forms Predominate
Freezing rain also usually occurs in winter, but it requires low temperatures on the ground, not the freezing air of hail. Of the three types, freezing rain is generally more dangerous to motorists than sleet and hail. Unlike sleet, which is more like a collection of grains, freezing rain creates a icy glaze that freezes streets and sidewalks, making driving and walking very dangerous. Freezing rain is a type of precipitation that occurs when liquid rain falls and then freezes as it hits cold surfaces such as tree branches, sidewalks, power lines, cars and roads.
Wet rain is a mixture of rain and snow and is a type of winter precipitation. When hail forms, raindrops blow from the bottom of the storm to the top, where they can freeze and turn into ice balls. From there, the ice particles then fall back to the bottom of the storm, where the raindrops collide with the small hailstones, which then rise again and freeze, making the hailstones a little bigger. The raindrops freeze into ice balls and then fall, collecting the raindrops in the hottest parts of the cloud layer until it is caught by the storm’s updraft and blown into the sky, where excess water settles.
As it falls softly into the storm, ice crystals and cloud droplets freeze on top of them and hang in the clouds for a while, picking up more of the frozen material. A melted snowflake never freezes, but instead melts completely under cold rain that freezes on contact with any surface below freezing.