NWS St. Louis Watch, Warning, and Advisory (WWA) Criteria

NWS St. Louis Announces Changes To May 16, 2025 Tornado Damage Assessment

After a year-long review of new ground survey data and aerial imagery, NWS St. Louis made several adjustments to the May 16, 2025 tornado damage assessment. Read More >

The below criteria is only valid within the NWS St. Louis County Warning Area (CWA). Click on the arrow next to each list to expand the table. Please note that Cold Weather Advisories and Extreme Cold Warnings have criteria that differ based on county. Refer to the attached map for the correct criteria.

Severe Weather
Flooding
Winter Weather
Cold
Heat
Non-Thunderstorm Wind
Fire Weather
Vision Obstruction
Frost/Freeze

Severe Weather

Severe Thunderstorm Watch	Potential for severe thunderstorms	Severe thunderstorms are possible in and near the watch area. Stay informed and be ready to act if a severe thunderstorm warning is issued. The watch area is typically large, covering numerous counties or even states.
Tornado Watch	Potential for tornadic storms	Tornadoes are possible in and near the watch area. Review and discuss your emergency plans, take inventory of your supplies and check your safe room. Be ready to act quickly if a warning is issued or you suspect a tornado is approaching. Acting early helps to save lives! Watches are issued by the Storm Prediction Center for counties where tornadoes may occur. The watch area is typically large, covering numerous counties or even states.
Severe Thunderstorm Warning	Hail of 1"+ in diameter or wind gusts 50kts+ (58mph)	Severe weather has been reported by spotters or indicated by radar. Warnings indicate imminent danger to life and property. Take shelter in a substantial building. Get out of mobile homes that can blow over in high winds. Warnings typically encompass a much smaller area (around the size of a city or small county) that may be impacted by a large hail or damaging wind identified by an NWS forecaster on radar or by a trained spotter/law enforcement who is watching the storm.
Tornado Warning	A tornado is strongly suspected or is occurring	A tornado has been sighted or indicated by weather radar. There is imminent danger to life and property. Move to an interior room on the lowest floor of a sturdy building. Avoid windows. If in a mobile home, a vehicle, or outdoors, move to the closest substantial shelter and protect yourself from flying debris. Warnings are issued by your local forecast office. Warnings typically encompass a much smaller area (around the size of a city or small county) that may be impacted by a tornado identified by a forecaster on radar or by a trained spotter/law enforcement who is watching the storm.

Flooding

Flood Watch	Potential for flash flood criteria
Flood Advisory	Nuisance flood that doesn't threaten to life or property
Flash Flood Warning	Short-term, rapid-onset flooding that require immediate action to protect lives and property
Flood Warning	Longer-term flooding that does not necessarily require immediate action, but still threatens life and property.

Winter Weather

Winter Weather Advisory	At least one of the following: Snow: 3-4" (lesser amounts if anticipated impacts are expected to be significant) Sleet: less than 1/2" Freezing Rain: less than 1/4" Freezing Drizzle: enough for a widespread glaze And may include: Wind Chill Blowing and Drifting Snow (wind gusts less than 35 mph and occasional visibilities 1/4 mile or less for 3+ hours)	Be prepared for winter driving conditions and possible travel difficulties. Use caution when driving.
Winter Storm Watch	Potential for Winter Storm/Blizzard/Ice Storm Warning criteria	Prepare for winter storm, ice storm, or blizzard conditions depending on the situation. Stay informed with the latest NWS forecast.
Winter Storm or Ice Storm Warning	At least one of the following: Heavy snow: 5"+ Sleet: 1/2"+ Freezing Rain: 1/4"+ And may include: Wind Chill Blowing and Drifting Snow Lesser amounts for snow, sleet, and freezing rain are possible if combined with a wind creating additional impacts (i.e., blowing/drifting of snow)	Winter Storm Warning: Travel will become difficult or impossible in some situations. Delay your travel plans until conditions improve. Ice Storm Warning: This amount of ice accumulation will make travel dangerous or impossible and likely lead to snapped power lines and falling tree branches. Travel is strongly discouraged.
Blizzard Warning	Persisting for 3+ hours: Sustained wind/frequent gusts to at least 35 mph Visibility 1/4 mile or less in falling/blowing snow	Falling and blowing snow with strong winds and poor visibilities are likely, leading to whiteout conditions making travel extremely difficult. Do not travel. If you must travel, have a winter survival kit with you. If you get stranded, stay with your vehicle and wait for help to arrive.
Snow Squall Warning	Heavy bursts of snow within a short period of time (usually less than one hour) causing rapid deterioration to travel conditions. Visibility 1/4 mile or less Wind gusts of at least 30mph Subfreezing roads or falling temperatures leading to a flash freeze. "General" Snow Squall Warnings will not trigger the WEA, and are issued when mitigating societal factors (time of day, day of week) exist. "Significant" warnings do trigger the WEA.	If a snow squall warning is issued for your area, avoid or delay motor travel until the squall passes through your location. There truly is no safe place on the highway during a snow squall. However if you are already in transit and cannot exit the road in time, reduce your speed, turn on your headlights and hazard lights and allow plenty of distance between you and the car in front of you. It’s also best not to slam on your brakes. With slick/icy roads, this could contribute to the loss of vehicle control and also increase the risk of a chain reaction crash.

Cold

Cold Weather Advisory	Please see this map for more detail
Extreme Cold Watch	Potential for Extreme Cold Warning criteria
Extreme Cold Warning	Please see this map for more detail

Heat

Heat Advisory	Max heat index of 105F+ for one day or 100F+ for at least 4 days
Extreme Heat Watch	Potential for Extreme Heat Warning criteria
Extreme Heat Warning	Max heat index of 110F+ and min heat index of 75F+ for 2+ days or Max heat index of 105F+ for at least 4 days

Non-Thunderstorm Wind

Wind Advisory	Sustained 30-39 mph (26-34kts) for 1+ hours Gust of 45-57 mph (39-49kts) for any duration
High Wind Watch	Potential for High Wind Warning criteria
High Wind Warning	Sustained 40+ mph (35kts) for 1+ hours Gust of 58+ mph (50kts) for any duration

Fire Weather

Elevated Fire Danger
Fire Weather Watch	Potential for Red Flag Warning criteria
Red Flag Warning	10-m sustained wind of > 17 mph (15 kts) Minimum RH of < 25% 10 hour fuel moisture < 9%

Vision Obstruction

Dense Fog Advisory	Visibilities of 1/4 mile or less due to fog, may include light accumulations of ice due to sub-freezing temperatures
Dense Smoke Advisory	Visibilities of 1/4 mile or less due to smoke

Frost/Freeze (these are agricultural products only issued in the growing season)

Frost Advisory	Widespread frost (temperatures in mid-30s, light winds, and dew potential)
Freeze Watch	Potential for widespread temperatures of 32F or below
Freeze Warning	Widespread temperatures of 32F or below