Winter Storm Warning: The Complete Guide
What is a winter storm warning?
A winter storm warning is issued by the National Weather Service (and equivalent national weather agencies worldwide) when a combination of hazardous winter weather — heavy snow, sleet, freezing rain, or ice — is occurring, imminent, or highly likely within the next 12 to 36 hours. A warning is one of the most serious winter alerts: it means the dangerous weather is no longer just possible, it is expected to happen and to threaten life and property. When a winter storm warning is in effect, you should avoid travel if at all possible and stay indoors.
Winter storm warning vs. watch vs. advisory
The three core winter alerts describe how certain and how severe the weather is:
| Alert | What it means | What to do |
|---|---|---|
| Winter Storm Watch | Conditions are favourable for a major winter storm within 12–48 hours. The storm is possible but not certain. | Be prepared. Review your plans and stock supplies. |
| Winter Weather Advisory | Less serious winter weather (typically lighter snow or ice) is expected. It is hazardous and inconvenient but not usually life-threatening if you are careful. | Use caution. Allow extra travel time. |
| Winter Storm Warning | Severe, life-threatening winter weather is occurring, imminent, or highly likely. | Take action now. Avoid travel; stay indoors. |
In one line: a watch means be prepared, an advisory means use caution, and a warning means take action now.
How much snow or ice triggers a winter storm warning?
Exact thresholds are set regionally — colder, snowier areas require more snow than milder ones — but in the United States a winter storm warning is typically issued for the following:
| Hazard | Typical warning threshold |
|---|---|
| Heavy snow (12 h) | ≥ ~6 inches (15 cm) |
| Heavy snow (24 h) | ≥ ~8 inches (20 cm) |
| Ice accumulation | ≥ ~¼ inch (6 mm) → often an Ice Storm Warning |
| Blizzard | Winds/gusts ≥ 35 mph + falling/blowing snow + visibility < ¼ mile for ≥ 3 hours → Blizzard Warning |
This site computes a transparent 0–100 winter-storm risk index from the live forecast using these same NWS-style thresholds, so you get a meaningful answer anywhere on Earth — even where no official alert feed exists. Where an official warning is available, it always takes priority and is clearly labelled.
What to do during a winter storm warning
- Avoid travel. If you must drive, tell someone your route and carry a winter survival kit (blanket, food, water, light, charger).
- Stay indoors and keep warm. Close off unused rooms and keep one room comfortable.
- Prepare for power outages. Charge devices and keep flashlights and batteries handy.
- Stock essentials — at least three days of food, water, and any medications.
- Check on others — elderly relatives, neighbours, and anyone living alone.
- Never heat your home with a stove, oven, or grill — carbon monoxide can be deadly.
- Protect pipes from freezing and know how to shut off your water.
Other winter weather alerts to know
- Blizzard Warning — sustained winds or frequent gusts of 35 mph or more with falling or blowing snow reducing visibility below ¼ mile for at least 3 hours. Blizzards are extremely dangerous; do not travel.
- Ice Storm Warning — significant ice accumulation, generally ¼ inch or more, capable of downing trees and power lines and making surfaces treacherous.
- Wind Chill / Extreme Cold Warning — dangerously cold wind chill values that can cause frostbite on exposed skin within minutes.
- Snow Squall Warning — a brief but intense burst of heavy snow and wind that causes sudden whiteouts and is a major cause of highway pile-ups.
Frequently asked questions
What does a winter storm warning mean?
It means heavy snow, sleet, or ice is occurring, imminent, or highly likely in your area and is expected to make travel dangerous and threaten life and property. Take action now: avoid travel and stay indoors if you can.
Is a winter storm warning worse than a watch?
Yes. A watch means a winter storm is possible within 12–48 hours, while a warning means the dangerous weather is happening or about to happen. A warning is more urgent than a watch.
How much snow triggers a winter storm warning?
Thresholds vary by region, but typically about 6 inches (15 cm) of snow in 12 hours or 8 inches (20 cm) in 24 hours, or roughly a quarter inch of ice. Snowier regions use higher thresholds.
How long does a winter storm warning last?
Usually 12 to 36 hours, with a specific start and end time set by the issuing weather agency. It is updated or cancelled as the storm evolves — check the effective and expiry times shown for your location above.
Should you go to work or school during a winter storm warning?
Follow official guidance from your employer, school district, and local authorities. Many close or delay during a warning. If travel is not essential, the safest choice is to stay home.
Check the winter storm warning for your city
See live winter storm warnings, conditions, and a 7-day snow forecast for major US cities, or let the tracker detect your location automatically:
Browse winter storm warnings by city →
Definitions on this page reflect criteria published by the U.S. National Weather Service. Thresholds vary by country and region; always defer to your national meteorological agency for the official warning in force where you are.