Explainers
What makes a blizzard, and what a Blizzard Warning means
By Ryan Hall, Y'all Weather Desk ยท Published
Written by our automated news desk from National Weather Service data.
Key points
- Blizzard: wind of 35 mph or more (sustained, or frequent gusts) with snow in the air, visibility often under 1/4 mile, for 3 hours or more.
- Snow totals don't decide it: blowing snow that already fell counts, so a blizzard can happen with little or no new snow.
- Ground blizzard: blizzard conditions caused only by blowing and drifting snow.
- Blizzard Warning: severe winter conditions are expected or occurring, with whiteouts that make travel extremely difficult.
- No separate Blizzard Watch: the national list has one winter watch, the Winter Storm Watch.
A blizzard is about wind and visibility, not how much snow falls. It takes sustained wind or frequent gusts of 35 mph or more, plus falling or blowing snow that often cuts visibility to less than 1/4 mile, lasting 3 hours or longer; a Blizzard Warning means those conditions are expected or already happening, and the advice is plain: do not travel.
These are the National Weather Service's own definitions, and they are the same ones we use on this site.
What makes a blizzard
Three things have to come together: strong wind, snow in the air, and poor visibility, and they have to last. The wind has to be sustained at 35 mph or more, or gust that high frequently. The snow, falling or blowing, has to frequently drop visibility to less than 1/4 mile. And all of it has to hold for 3 hours or longer.
A short burst of gusty snow doesn't meet that. A long stretch of wind and whiteout does.
Notice what is missing: a snow total. A foot of calm snow isn't a blizzard. Little or no new snow can still produce one when the wind, visibility and duration criteria are met.
Ground blizzards
Snow doesn't have to be falling for a blizzard to happen. Wind can pick up snow already on the ground and throw it back into the air, which hurts visibility just as much. When blizzard conditions come only from blowing and drifting snow, it's called a ground blizzard.
Watches: there is no Blizzard Watch
You may go looking for a Blizzard Watch and not find one. The current national instruction lists one winter watch, the Winter Storm Watch. It covers snow and blowing snow among its hazards. That watch covers snow and blowing snow among its hazards; there is no separate watch with "blizzard" in the name.
You can see every watch and warning in effect right now on our warnings page.
What a Blizzard Warning means
A Blizzard Warning means severe winter weather is expected or already happening. Falling and blowing snow, strong wind and poor visibility are likely. That can lead to whiteout conditions that make travel extremely difficult.
Because the warning rests on wind and visibility, don't judge it by the snow total. A warning with modest snowfall still means the same thing: the wind can turn even a little snow into a whiteout. The snow doesn't have to be new, either.
What to do
- Do not travel. This is the main message of a Blizzard Warning. If you can put off the drive, put it off, and check our interstate driving outlook before you decide anything.
- If you must travel, carry a winter survival kit in your vehicle.
- If you get stranded, stay with your vehicle and wait for help to arrive. A vehicle is easier for rescuers to find than a person on foot in a whiteout.
Want a heads-up before the next one? You can sign up for free Y'all Alerts.
For the latest on where wind and snow are lining up, see our winter storm outlook.
More on Weather explainers
Sources
- NWS Instruction 10-513, "WFO Winter Weather Products Specification" (November 6, 2024), Table 1, NOAA National Weather Service, issued
- NWS safety page "Winter Weather Warnings, Watches and Advisories", NOAA National Weather Service
- NWS Glossary, "blizzard", NOAA National Weather Service