GRAND RAPIDS, Michigan — When winter weather is set to impact West Michigan, the National Weather Service (NWS) can issue warnings and advisories for counties and cities ahead of the storm. But in order to issue a warning or advisory, the storm must be expected to meet certain criteria.
Here's what criteria the different issuances need:
What is a Winter Storm Warning?
The NWS will issue a winter storm warning when any of the following conditions are expected within the next 12 to 36 hours:
- Blizzard conditions with sustained winds or frequent gusts of at least 35 mph and considerable falling and/or blowing snow frequently reducing visibility below a quarter mile for at least 3 hours (Blizzard conditions need to be the predominant condition over a 3 hour period)
- Heavy snowfall of at least eight inches or more in 12+ hours or six inches or more in six to nine hours
- Ice accumulation of half an inch or greater in any zone
- Pure sleet of at least an inch
- A wind chill index less than -35°F for at least 3 hours with a sustained wind of at least 10 mph
- A winter weather event having more than one predominant hazard (i.e. heavy snow and blowing snow, snow and ice, snow and sleet, sleet and ice, or snow, sleet and ice) meeting or exceeding warning criteria for at least one of the precipitation elements
What is a Winter Weather Advisory?
The NWS will issue a winter weather advisory when any of the following conditions are expected within the next 12 to 24 hours:
- Blowing snow causing visibility to be reduced over a wide area due to wind-driven snow with winds less than 35 mph. Usually not issued for localized occurrences
- Any accretion of freezing rain or freezing drizzle on road surfaces
- Winter weather event having more than one predominant hazard (i.e., snow and ice, snow and sleet, or snow, ice & sleet) meeting or exceeding advisory criteria for at least one of the precipitation elements, but remaining below warning criteria
- 4 inches averaged over a forecast zone in 12 hours
- 4 inches snowfall averaged over a forecast zone in 12 hours with visibility substantially reduced over a wide area due to wind-driven snow with winds less than 35 mph
- Wind chill index between -20°F and -34°F for at least 3 hours with a sustained wind speed of at least 10 mph
What is a Snow Squall Warning?
The NWS defines a snow squall warning as a "Brief quick hitting white-out conditions in heavy snow and blowing snow."
You can learn more about snow squalls and how to stay safe in them here.