Weather Advisory, Watch, and Warning Criteria

All data from the Atlanta NWS

WATCHES	A watch is issued when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location or timing is still uncertain. A watch means that hazardous weather is possible. People should have a plan of action in case a storm threatens and they should listen for later information and possible warnings especially when planning travel or outdoor activities.
WARNINGS	A warning is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. A warning means weather conditions pose a threat to life or property. People in the path of the storm need to take protective action.
ADVISORIES	An advisory is issued when a hazardous weather or hydrologic event is occurring, imminent or likely. Advisories are for less serious conditions than warnings, that cause significant inconvenience and if caution is not exercised, could lead to situations that may threaten life or property.
Each NWS office can and does modify the watch/warning criteria to fit their local, so these may be outdated. Where I have the Atlanta modifications, they will appear in bold just at the end of the product description.

WINTER SEASON WATCHES, WARNINGS, and ADVISORIES

Here's a basic look at the watch/warning criteria for winter weather events in Georgia. More specific information is in the detail below the images.

WINTER ADVISORIES and OUTLOOKS

Starting in the Winter of 2024-2025, Wind Chill Warning and Advisory products are no longer issued by NWS. They've been replaced with "Extreme Cold Watch & Warning" and "Cold Weather Advisory". These new products include both actual air temperature as well as wind chill values. The criteria for issuance for these products will vary based on location within Georgia, with the coldest thresholds in north Georgia and warmer thresholds in central Georgia accounting for climatology.

Snow Advisory

A Snow Advisory will be issued when 3-5 inches is expected to fall.
*Check with your NWS office for local snowfall requirements.

Blowing Snow Advisory

A Blowing Snow advisory will be posted for events in which visibility is intermittently 1/4 mile or less.

Freezing Rain/Drizzle Advisory

This requires that hazardous driving conditions be taking place and/or up to 1/4 inch of freezing rain on tree branches and/or if power lines break.

Winter Weather Advisory

Issued up to 36 hours before an event for an 80% or greater chance of a winter precipitation event (snow, freezing rain/drizzle, sleet or blowing snow) which causes inconveniences but does not meet warning criteria. Issued as WSWFFC.

Winter Storm Outlook

Issued 3-7 days before an event for a 30% or greater chance of a hazardous winter weather event that may require a watch/warning in a later forecast. Issued via the Hazardous Weather Outlook (HWOFFC) or Special Weather Statement (SPSFFC).

WINTER STORM WATCHES

Winter Storm Watch

Issued 12-48 hours in advance of an event for a 50% or greater chance of conditions favorable for a significant winter storm (including heavy sleet, heavy snow, or ice storm). Winter storm conditions include 2 ormore inches of snow, 1/2 inch or more of sleet, or 1/4 inch or more of greezing rain Issued as WSWFFC.

Blizzard Watch

Issued 12-48 hours before an event for a 50% or greater chance of blizzard conditions. Blizzard conditions include sustained or frequent wind gusts of 35mph or greater and considerable falling and/or blowing snow reducing visibility to less than 1/4 mile for 3 hours or more. Issued as WSWFFC.

WINTER STORM WARNINGS

Winter Storm Warning

Issued up to 36 hours before an event for an 80% or greater chance of winter weather event that meets at least one of these criteria:

2 or more inches of snow
½ inch or more of sleet
¼ inch or more of freezing rain

These thresholds may be adjusted down in cases where the expected impacts will be especially significant, for instance when less than 2 inches of snow falls on very cold ground or during times when the affected population will be especially vulnerable.
Issued as WSWFFC.

Blizzard Warning

Issued up to 36 hours before an event for an 80% or greater chance of sustained or frequent wind gusts to 35mph or greater and considerable falling and/or blowing snow reducing visibility to less than 1/4 mile for 3 hours or more. Issued as WSWFFC.

Ice Storm Warning

Issued up to 36 hours before an event for an 80% or greater chance of a 1/4 inch or more of freezing rain. Issued as WSWFFC.

Heavy Snow Warning

A Heavy Snow Warning will be issued if 6 or more inches of snow is expected in a 12 hour period. (Wind chill and Frost/Freeze products are found in the non-precipitation section).

WARM SEASON WATCHES, WARNINGS and ADVISORIES

Tornado Watch: A Tornado Watch will be issued when conditions are favorable for the development of severe thunderstorms and tornadoes. The Storm Prediction Center (SPC) is the sole agency responsible for issuing a watch. A watch covers several thousands of square miles and generally lasts from two to six hours. Keep an eye on the sky for changing conditions and make preparations in case a weather warning is issued.
Severe Thunderstorm Watch: A Severe Thunderstorm Watch will be issued when conditions are favorable for development of severe thunderstorms. While not anticipated, tornadoes may occur in the watch area. The Storms Prediction Center (SPC) is the sole agency responsible for issuing a watch. A watch covers several thousands of square miles and generally lasts from two to six hours. Keep an eye on the sky for changing conditions and make preparations in case a weather warning is issued.
Flood Watch: A Flood Watch will be issued for situations related to widespread general flooding.
Flash Flood Watch: A Flash Flood Watch will be issued for serious situations in which life and/or property are in danger. Flash Flood watch covers flash flooding, widespread urban and small stream, and headwater flood events.
Fire Weather Watch: A fire weather watch means that there is high potential for the development of critical fire weather conditions in 12 to 96 hours. Conditions generally include very low humidities (25% or lower) and high winds (above 15-20mph).

Tornado Warning

When a Tornado Warning is issued, tornadoes are occurring, imminent, or has has been spotted or detected by radar. There is imminent danger for people in the area warned. Issued by a local NWS office, the size of the warning area is generally the size of one or two counties and usually lasts less than an hour. Stay away from windows, doors and outside walls. Put as many walls between you and the tornado as possible on the lowest floor of your building. If you do not have a basement, seek shelter in an interior bathroom or closet. Get under something sturdy. Protect your head. Stay away from mobile homes. Get out of your vehicle. If there is no safe shelter, lie flat in the nearest ditch or ravine with your hands shielding your head.

Severe Thunderstorm Warning

A warning issued to warn the public of an existing, imminent or suspected severe thunderstorm. The National Weather Service (NWS) defines a severe thunderstorm as having winds 50 kts (58 mph) or hail greater than 1" in diameter (about quarter-sized). (A storm that spawns a tornado is obviously also considered severe.) There is imminent danger for people in the area warned. Issued by a local NWS office, the size of the warning area is generally the size of one or two counties and usually lasts less than an hour. Stay away from windows, doors and outside walls. Put as many walls between you and the tornado as possible on the lowest floor of your building. If you do not have a basement, seek shelter in an interior bathroom or closet. Get under something sturdy. Protect your head. Stay away from mobile homes. Get out of your vehicle. If there is no safe shelter, lie flat in the nearest ditch or ravine with your hands shielding your head.

Flood Warning

For all areas other than a forecast points, used to issue a flood warning in situations where flooding is expected to occur more than 6 hours after a heavy rain event. Also...issued when flash flooding persists longer than 6 hours.

River Flood Warning

Issued when the river stage at a forecast point is expected to reach or exceed bankfull (flood stage), causing the inundation of a normally dry area.

Flash Flood Warning

A warning issued to warn the public that flash flooding is imminent or in progress. A flash flood is a flood which is caused by heavy or excessive rainfall in a short period of time, generally less than 6 hours. Also, a dam failure can cause a flash flood.

Small Stream Flood Warning

Advisory

An Urban and Small Streams Flood Warnings or Advisories are issued when flooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains, is occurring.

Special Weather Statement

Issued to convey information about an upcoming weather event that is expected to be significant, but not meeting criteria for a Watch, Warning, or Advisory.

NON-PRECIPITATION WATCHES/WARNINGS/ADVISORIES

High Wind Watch: Issued when, during the next 48 hours, there is at least a 50 percent chance of sustained wind speeds of at least 36 mph lasting 1 hour or more. Also issued when there is a 50 percent chance of a wind gust of 45 mph.
Frost Outlook: Issued when, within the next 24 to 48 hours, there is a moderate probability (50% - 70%) of significant frost. These are issued on, or after March 20th in Spring, and prior to November 20th in Autumn. In Autumn, the issuance of Frost Outlooks will be discontinued prior to November 20 if temperatures fall below 28 degrees over a wide area.
High Wind Warning: Issued when, during the next 24 hours, there is at least an 80 percent chance of sustained wind speeds of at least 36 mph lasting 1 hour or more. Also issued when there is an 80 percent chance of a wind gust of at least 45 mph.
Wind Advisory: Issued when, during the next 24 hours, there is at least an 80 percent chance of wind speeds 20 to 35 mph lasting for one hour or longer...OR when wind gusts of at least 35 mph are expected.
Dense Fog Advisory: Issued when, during the next 24 hours, there is at least an 80 percent chance of widespread visibility restrictions of 1/4 mile or less.
Heat Advisory: Issued when there is at least an 80 percent chance that daytime heat indices will exceed 104 degrees AND nighttime lows will be no lower than 75 degrees for at least 2 consecutive days.
Excessive Heat Warning: Issued when there is at least an 80 percent chance that daytime heat indices will exceed 109 degrees AND nighttime lows will be no lower than 75 degrees for at least 2 consecutive days.
Frost Advisory: Iissued up to 24 hours in advance when there is high confidence (>80% chance) of a significant frost with minimum temperatures of 33°F to 36°F during the growing season.
Freeze Watch: Issued up to 48 hours in advance when there is medium confidence (>50% chance) of minimum temperatures at or below 32°F during the growing season.
Freeze Warning: Issued up to 24 hours in advance when there is high confidence (>80% chance) of minimum temperatures at or below 32°F during the growing season.