A Winter Weather Advisory is a National Weather Service alert for snow, blowing snow, sleet, freezing rain or a mix of them that is expected to meet local advisory criteria but stay below warning levels. It describes conditions that are a significant inconvenience and could lead to dangerous situations if people do not use caution.
What falls under it
NWS Instruction 10-513 lists hazards such as snow, snow with blowing snow, mixes of snow, sleet and ice, freezing rain, and lake-effect snow. At least one precipitation element has to meet locally defined 12-hour or 24-hour advisory criteria without exceeding warning criteria, and the directive also allows advisories based on impact-driven criteria.
Since 10/01/17, this single advisory has replaced the former Freezing Rain Advisory and Lake Effect Snow Advisory, so the text, not the headline, tells you which hazard is expected.
Office examples
Criteria vary by office. The Twin Cities office uses 3 to less than 6 inches of snow, and the Lincoln, Illinois office lists snow of 3 to 5 inches in 12 hours, sleet up to 1/4 inch, freezing rain mixed with sleet or snow, or blowing snow.
For ice, the Des Moines office treats freezing rain or drizzle of less than 1/4 inch as advisory level. Larger ice amounts move into Ice Storm Warning territory.
Why the lower tier still matters
The NWS notes that even small accumulations of ice can be extremely dangerous to motorists and pedestrians, and that bridges and overpasses freeze before other surfaces.
An advisory can also be the backdrop for a short, sharper hazard. The directive allows Snow Squall Warnings during a Winter Weather Advisory if conditions are expected to worsen for a brief period.
A planned headline change
The NWS Hazard Simplification project has said it plans to drop the "Advisory" headline in favor of plain-language headlines, with at least six months of public notice before implementation. The November 2024 version of the winter directive still uses the Winter Weather Advisory name, so check current NWS notices for the status of that change.