A lot of you may have been surprised today when you noticed the rain start to bounce. Turns out, some of that rain was actually ice called sleet that some people confused as hail. What’s the difference?
Sleet: ice pellets made from frozen raindrops or melting snowflakes
Sleet forms as precipitation travels through a wide range of temperatures on its way to the ground, including layers of air that are both above and below freezing. Sometimes snow falls into warmer temperatures on its way to the ground and partially melts. Other times, raindrops enter colder temperatures near the earth’s surface and partially freeze before reaching the ground. If enough sleet pellets fall and accumulate, it can resemble snow on the ground.
Hail: round stones of ice that tend to be clear, and usually form in thunderstorms. can happen anytime of year, even in warm weather
Within a thunderstorm, there are areas of rising and sinking air. This causes rain droplets to rise into colder temperatures. If it’s cold enough, the rain will freeze into a hailstone and begin to fall back down. If the thunderstorm is strong enough, it’ll lift the hailstone up main times before it can fall to the ground. Each time the hail stone rises, it collects more layers of ice. Therefore, very large hail stones come from very strong thunderstorms. Larger hail stones are obviously more dangerous and more damaging.
Freezing Rain: very cold rain that freezes instantly when it hits the ground, forming a thin layer of ice
It happens when rain travels through a very shallow layer of cold temperatures near the earth’s surface. There’s not enough time for it to freeze into sleet, but it does cool down enough to freeze instantly when it hits the ground, forming a thin layer of ice on anything it touches, like roads, sidewalks, tree branches and power lines. Not only does it make for slippery travels, if enough ice collects, it can even be heavy enough to break tree branches and bring down power lines.
Snow: crystals of ice that come in many shapes and sizes
Light, fluffy snow usually happens in very cold temperatures, and can pile up very quickly, making it hard to travel. Heavy, wet snow forms in slightly warmer temperatures, and can cause problems when it weighs down on trees branches, power lines and roofs. Snow causes the roads to become very slippery, especially as it begins to melt and then refreezes into ice.
Graupel: white snow pellets that resemble soft, milky colored hail stones
Graupel is the least familiar of all types of frozen precipitation, it is often confused with hail because it looks very similar, except that it forms through a completely different process. It usually forms when water droplets run into snow and instantly freeze. The easiest way to tell it apart from hail is that it is usually opaque and milky looking, while hail tends to be more clear. Hail tends to be associated with warm weather thunderstorms, while graupel is more common in cold weather, when no thunderstorms are present.
Today’s icy mix was indeed sleet, as seen by this diagram:
This is called a Skew-T diagram, and it contains weather data from a balloon launched in Sterling, Virginia this morning. The balloon carries an instrument called a radiosonde that measures temperature, moisture and winds at different levels in the atmosphere.
While temperatures were above freezing at the surface at the time of the sleet, in the low 40s to be exact, the temperature graph shows that there was a shallow layer of subfreezing temperatures just above the surface. That layer was cold enough for some rain to freeze into sleet.
– Meteorologist Ava Marie, 11/13/2012 1 pm