Slow down on bridges and overpasses in freezing weather, stay off the road if you can, and stay off lake ice that is under 4 inches thick.
| Ice thickness (NWS) | Use |
|---|---|
| Under 2 inches | Stay off |
| 4 inches or more | Ice fishing, skating or walking |
| At least 5 inches | Snowmobiles and ATVs |
| 8 to 12 inches | A car or small pickup |
| 12 to 15 inches | Medium-sized trucks |
Ice storm impacts
Heavy ice can bring down trees, utility poles and communication towers. Outages to communications and power can last days while utilities make repairs. Even a thin layer of ice is dangerous to drivers and pedestrians, and bridges and overpasses freeze before other surfaces.
Freezing rain vs sleet
The NWS glossary defines freezing rain as rain that falls as a liquid but freezes into glaze on contact with the ground. Sleet is pellets of ice composed of frozen or mostly frozen raindrops or refrozen partially melted snowflakes, and the pellets often bounce when they hit the ground. Heavy sleet is uncommon and means ice pellets build up to at least half an inch deep.
What makes an ice storm
The NWS defines an ice storm as freezing rain expected to create damaging ice buildup, which can bring down trees and power lines, cause power and communication outages, and make walking and driving very dangerous. Significant ice accumulations are usually a quarter inch or more, and an Ice Storm Warning typically is issued when more than a quarter inch of ice is expected, though criteria vary by state.
Freezing rain advisory
A Freezing Rain Advisory is issued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. The NWS adds that even small amounts of freezing rain or freezing drizzle may cause significant travel problems.
Black ice
Black ice is a thin, patchy layer of ice on roads that is hard to see. It is most common in early morning, especially when melted snow refreezes overnight. It can also form when rain leaves roads wet and temperatures fall below freezing overnight.
Ice jams
During long cold spells rivers and lakes can freeze. When the water rises or temperatures warm, the ice breaks into chunks that jam against obstructions and can act like dams and cause severe flooding.
Ice safety on lakes and streams
Check with local officials, such as a state Department of Natural Resources, before going on ice. Stay off if you see cracks, holes or breaks, water flowing at the edges or over the ice, or ice that has thawed and refrozen. White or snow ice is about half as strong as clear ice, so double the thicknesses in the table.
Related alerts
See the winter alerts page for active ice storm and winter weather alerts, and our guide to power outages and heating safety.
Check your own location
See current official alerts and the impact for your ZIP code.
Common questions
What is the difference between freezing rain and sleet?
Freezing rain falls as liquid and freezes into glaze on contact with the ground. Sleet is pellets of ice made of frozen or mostly frozen raindrops or refrozen partly melted snowflakes, and it often bounces when it hits the ground.
What is an ice storm?
Freezing rain expected to create damaging ice buildup that can bring down trees and power lines and make walking and driving very dangerous. The NWS says significant accumulations are usually a quarter inch or more.
What is black ice?
A thin, patchy layer of ice on roads that is hard to see, often clear so the dark pavement shows through. It is most common in early morning, especially when melted snow refreezes overnight, and can also form when rain leaves roads wet and temperatures drop below freezing overnight.
Why do bridges freeze first?
The National Weather Service says bridges and overpasses freeze before other surfaces, so slow down on them in freezing weather.
How thick should ice be to walk on?
The NWS gives 4 inches or more for ice fishing, skating or walking, and says to stay off ice under 2 inches. White or snow ice is about half as strong as clear ice, so double the thickness. Always check with local officials first.
Sources
Reviewed by the Storm Incoming editorial team on October 27, 2026. Follow local emergency officials if their instructions differ.