Sleet is rain that freezes into ice pellets before it hits the ground, while freezing rain falls as liquid and freezes on contact with surfaces.
Sleet
Rain freezes into ice pellets before landing. It bounces and makes a tapping sound.
Freezing rain
Rain stays liquid in the air, then freezes on contact with cold surfaces. It makes a glaze of ice.
Danger
Freezing rain is more dangerous. Even a quarter inch of ice can bring down power lines and make roads treacherous.
Why
A warm layer aloft melts snow. Below it is a cold layer: a deep one makes sleet, a shallow one makes freezing rain.
How each forms
Both start as snow in the upper atmosphere that falls into a layer of warmer air and melts into rain. The difference lies in the layer near the ground. If there is a deep layer of below freezing air near the surface, raindrops freeze again into small ice pellets (sleet). If the cold layer is shallow, the raindrops stay liquid and freeze on contact with surfaces below 32 degrees F (0 degrees C): freezing rain.
Appearance and sound
Sleet bounces and makes a tapping sound on windows. Freezing rain coats surfaces with a clear glaze of ice.
Size
Sleet pellets are small, usually less than 5 millimeters across.
Danger
Freezing rain is more hazardous. The National Weather Service says as little as 1/4 inch of ice accumulation can bring down tree limbs and power lines, and roads become very slippery. A half inch of ice on power lines can add 500 pounds of weight per line span.
Impact on travel
Freezing rain can cause “black ice,” a thin transparent layer on pavement that is hard to see. Drivers should slow down or stay off the roads.
Safety tips
- Stay home during ice storms if possible.
- Keep flashlights, batteries, water and blankets ready for power outages.
- Never use a generator or grill indoors because of carbon monoxide.
- Walk with small steps and use salt or sand on walkways.
Sleet versus hail
Hail forms in thunderstorms and is larger, while sleet falls in winter weather.
Snow
If the whole column is below freezing, precipitation falls as snow.
Formation processes
Sleet, called ice pellets by the National Weather Service, forms when snow falls through a layer of warm air, melts to rain, then passes through a deep layer of freezing air near the ground and refreezes into small ice pellets before landing. They bounce and make a tapping sound. Freezing rain falls as liquid raindrops through a shallow layer of freezing air at the surface and freezes on contact with surfaces below 32 F, coating roads, trees and power lines with glaze ice. In the UK, “sleet” means a mix of rain and snow, which is different from the US meaning.
Hazards and safety
Freezing rain is far more dangerous than sleet. An accumulation of a quarter inch of ice can bring down tree limbs and power lines, and half an inch or more can cause widespread outages, according to the NWS. Roads covered in glaze ice can be nearly impossible to drive on. Stay home if possible, keep a flashlight, battery radio, water and blankets, and never run a generator indoors. Hail is different, as it forms in thunderstorms from layers of ice in strong updrafts and can be much larger. Treat steps with salt or sand and wear shoes with good traction.
Based on data from the National Weather Service and NOAA
