National Weather Service United States Department of Commerce

Local National Weather Service offices issue Winter Storm Warnings, Winter Storm Watches, and Winter Weather Advisories.  What do these different products mean? This graphic breaks down the criteria for issuance here in central Illinois:

Winter weather headline criteria

Normally, a Winter Storm Watch will be issued in advance of the storm (usually at least 24 hours). It indicates the risk of a hazardous winter weather event has increased (at least a 50% chance of it occurring), but its occurrence, location, and/or timing is still uncertain. It is intended to provide enough lead time so you can make plans to stay safe. While rare for our area, a Blizzard Watch may be issued instead. 

As the event becomes imminent, a watch will normally be upgraded to either a warning or an advisory (which indicates an 80% or greater probability of occurence). A Warning indicates that conditions pose a threat to life or property, and that travel will become difficult to impossible. An Advisory indicates conditions pose a significant inconvenience, and if caution is not exercised, could lead to situations that may threaten life and/or property. 

There are 3 types of warnings issued by our office:

  • A Winter Storm Warning indicates that heavy snow of at least 6 inches in 12 hours, or at least 8 inches in 24 hours, is expected. It can also be issued if sleet accumulation will be at least half an inch. 
  • An Ice Storm Warning indicates that ice accumulation of at least 1/4 inch is expected.
  • A Blizzard Warning indicates that blizzard conditions (low visibility of less than 1/4 mile due to falling and/or blowing snow, and winds at least 35 mph) are expected for at least 3 hours. 

There are two types of advisories issued by our office:

  • A Freezing Rain Advisory indicates that ice accumulation of up to 1/4 inch is expected.
  • A Winter Weather Advisory is issued for one or more of the following:  Snow of 3 to 5 inches in 12 hours, sleet accumulation up to 1/4 inch, freezing rain in combination with sleet and/or snow, or blowing snow. 

For more winter preparedness information, visit our Winter Weather Preparedness page.