Winter Weather Glossary
Plain-language definitions for snow, ice, and winter storm terminology
See definitions next to the tools that use them — like the Wind Chill Calculator, Black Ice Calculator, Snowfall Predictor, and our FAQ.
Winter weather reports are full of specialized terms - blizzard, wind chill, lake effect snow, and more. This glossary explains the vocabulary you will hear in forecasts, school announcements, and news coverage across the United States and Canada.
See definitions next to the tools that use them — like the Wind Chill Calculator, Black Ice Calculator, Snowfall Predictor, and our FAQ.
Terms are organized by category. For deeper guides on school closures, storm safety, and driving, visit our Weather Guides or browse related calculators on the Calculators page.
Storms & Precipitation
- Blizzard
- A severe winter storm with sustained winds of at least 35 mph, visibility reduced to ¼ mile or less, and blowing or falling snow lasting three hours or more. Blizzards create whiteout conditions and make travel extremely dangerous.
- Snow Squall
- A brief but intense burst of heavy snowfall, often accompanied by gusty winds and a sudden drop in visibility. Snow squalls can cause multi-vehicle accidents on highways within minutes.
- Lake Effect Snow
- Snow produced when cold air moves across warmer lake water, picking up moisture that falls as heavy bands of snow downwind. Common near the Great Lakes and other large bodies of water.
- Freezing Rain
- Rain that falls as liquid but freezes upon contact with surfaces at or below 32°F (0°C). Creates a glaze of ice on roads, power lines, and trees - often more hazardous than snow alone.
- Sleet
- Ice pellets that form when raindrops freeze before reaching the ground. Sleet bounces on impact and can make roads slippery, though it is generally less dangerous than freezing rain.
- Snow Accumulation
- The total depth of snow that has fallen and settled on the ground, typically measured in inches or centimeters over a set period (such as 24 hours).
Ice & Road Hazards
- Black Ice
- A thin, transparent layer of ice on pavement that is nearly invisible to drivers. Black ice forms most often on bridges, overpasses, and shaded road sections when temperatures hover near freezing.
- Ice Storm
- A storm that produces significant accumulation of freezing rain, coating surfaces with ice. Ice storms can down power lines and tree limbs, causing widespread outages.
- Hard Freeze
- When air temperature drops to 28°F (−2°C) or below for several hours, causing standing water and wet pavement to freeze solid.
Temperature & Wind
- Wind Chill
- The perceived temperature on exposed skin, accounting for heat loss caused by wind. A wind chill of −20°F can cause frostbite in under 30 minutes.
- Feels-Like Temperature
- A combined measure of actual air temperature and wind chill (or heat index in summer). Our Feels-Like Calculator computes this from live forecast data.
- Polar Vortex
- A large area of low pressure and cold air surrounding the Earth's poles. When the polar vortex weakens, frigid Arctic air can plunge southward into the US and Canada.
School & Schedule Terms
- Snow Day
- A day when schools close due to hazardous winter weather conditions such as heavy snow, ice, extreme cold, or poor visibility. Districts typically announce snow days early in the morning.
- Two-Hour Delay
- A schedule modification that pushes back school start times by two hours, giving road crews time to plow and treat surfaces before buses run. Also called a late start.
- Early Dismissal
- When schools release students ahead of the normal schedule because worsening weather is expected during the afternoon commute.
- E-Learning Day
- A remote instruction day used by some districts instead of a traditional snow day. Students complete assignments online while buildings remain closed.
Alerts & Advisories
- Winter Storm Watch
- Issued when conditions are favorable for a significant winter storm within the next 24 to 48 hours. It is a heads-up to begin preparation.
- Winter Storm Warning
- Issued when a significant winter storm is occurring or imminent. Heavy snow, ice, or a combination is expected to cause serious impacts.
- Winter Weather Advisory
- Issued for winter weather that will cause inconvenience but is not expected to reach warning-level severity. Still requires caution when traveling.
For a full explanation of how to respond to each alert type, read our guide on Understanding Winter Weather Alerts.