Ice Storms, Black Ice and Ice Thickness: NWS Winter Ice Safety Explained
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How we wrote this: A plain-English summary of National Weather Service safety guidance, checked October 29, 2026. Always follow your local NWS forecast office. Ice thickness varies; check with local officials before going on any ice.
Ice storms
Heavy ice can bring down trees and topple utility poles and towers, cutting power and communications for days. Even a thin coat of ice is dangerous for drivers and walkers. Bridges and overpasses freeze first.
Black ice
Black ice is patchy, clear ice on roads that's hard to see, because the dark pavement shows through. It's most common in the early morning, especially when snowmelt refreezes overnight. It can also form when wet roads drop below freezing.
Ice jams
Long cold spells freeze rivers and lakes. A thaw or rising water breaks the ice into chunks that jam at obstructions, and a jam can act like a dam and cause severe flooding.
Ice on lakes and ponds
Check with local officials, such as your state Department of Natural Resources, first. Don't go out if you see:
- cracks, holes or breaks;
- flowing water at the edges, just below the surface or on top;
- ice that looks thawed and refrozen.
| Activity | NWS guideline (new, clear ice) |
|---|---|
| Stay off | Less than 2 inches |
| Ice fishing, skating, walking | 4 inches or more |
| Car or small pickup | 8 to 12 inches |
White ("snow") ice is about half as strong as new, clear ice, so double these numbers on white ice.
Frost
Frost is thin ice crystals that form on surfaces when they cool below 32°F. Because surfaces cool by radiating heat, frost often forms when a thermometer reads in the mid-30s. A frost hard enough to end the growing season is a "killing frost."
Related: snow squalls, wind chill and hypothermia, winter weather alerts.