As the season for storms rapidly approaches, it seems like a good time to clarify the terms for different warnings. Just what is an advisory, watch, or warning? Which is more severe and requires immediate action and which requires a person to just pay a little more attention to the weather? Everyone has heard these terms, but not every term is applied to every type of weather. There are no fire weather advisories; just watches and warnings. Some advisories, watches, and warnings vary by location. For example, wind chill warnings may be issued at higher temperatures in states that do not often have wind chill concerns and be issued at lower temperatures in areas used to more cold. Global warming and climate change may introduce some of these hazards into areas that until now had no experience with them.
Thunderstorms have a separate scale beyond watches and warnings because severe thunderstorms can lead to tornadoes and derechos. The scale for thunderstorms is in a separate section of text below.
In general, an advisory is issued when special weather conditions exist but the conditions are less serious than either a watch or a warning. The weather events have the potential to cause some inconvenience, and even situations that threaten life and or property if care is not taken. For example, a frost advisory will be issued when the temperature is forecast to be between 33 and 36 degrees and the cold temperatures could damage crops or plants. A gardener or farmer may get lucky and his plants will be unharmed, or he might want to take steps to protect his plants. The advisory lets him know that there is the possibility of damage due to weather to his property. But it is just a possibility, not a probability.
As mentioned earlier, some advisories vary by territory. This applies particularly to small watercraft, and areas involved can include rivers, bays, and oceans and their varying natures. Advisories may also be issued for small craft when ice exists in the water that could be hazardous to small boats. There is no definition of "small craft"; it is up to the individual person to determine whether or not his boat is of such a size that small craft warnings would apply to his craft.
Air quality does not follow the typical advisory, watches, or warnings. It has a separate scale that indicates the level of air pollution and when the air is unhealthy at various levels. Air quality levels have been entered into the category that best fits. Good air is considered green, and the index is between 0 to 50. Moderate air quality is between 51 to 100 and is yellow. All others are hazardous to some extent.
A new type of advisory has been developed this year, the Potential Tropical Cyclone (PTC) advisory. These storms are not yet tropical depressions, but have the chance of intensifying and becoming tropical storm or hurricane conditions to land within the next forty-eight hours. The designation allows forecasters to provide guidance for impacts to land before the storm is fully developed. Potential tropical cyclones will have the same numbering scheme as tropical depressions. A storm with stay a PTC until it intensifies to a tropical depression. The term has not yet been added to the National Weather Service glossary.
| Type of Weather | Nature of Advisory |
| Freezing Rain Advisory | Ice accumulations of less than ¼ inch. |
| Frost Advisory | Temperatures predicted to be between 33 and 36 degrees on clear and calm nights. Issued in the autumn until the end of growing season and in the spring at the start of growing season. |
| Wind Chill Advisory | Issued when wind chills of -5F to -19F are expected in certain areas, and -10 to -24 in other areas. |
| Dense Fog Advisory | Widespread fog is expected to reduce visibilities to ¼ mile or less over a large area for two or more hours. |
| Wind Advisory | Sustained winds of 31 to 39 miles per hour are expected for an hour or more, or gusts of 46 to 57 miles per hour are expected for any duration. |
| Small Craft Advisory
| Either sustained winds of 18 to 33 knots or frequent gusts between 18 and 33 knots or waves four feet or higher are expected within the next thirty-six hours. Varies by geographic area; this is for the Tidal Potomac River and Chesapeake Bay. |
| Heat Advisory | The heat index is expected to reach 105 to 109 within the next twelve to twenty-four hours. This is seasonally dependent and may be issued at lower temperatures if it is early in the season or expected to last for multiple days. The heat index is a measure of how hot it really feels when the humidity is added to the actual air temperature. |
| Tropical Advisory | Issued by cyclone warning centers to describe tropical cyclone conditions including location, intensity, and movement before watches and warnings are issued. It lets people know that a cyclone exists and could grow stronger and approach their area. A cyclone is a hurricane, just in different regions. The storms are hurricanes when in the Atlantic, Caribbean Sea, Gulf of Mexico, or eastern Pacific. Elsewhere they are cyclones. |
| Coastal Flood Advisory | Issued when minor or nuisance flooding is occurring or imminent. Varies by area; this is for the Tidal Potomac River and Chesapeake Bay. |
| Air Quality Orange | Unhealthy for sensitive groups, index between 101 to 150. Sensitive groups are the elderly, children, those with asthma, COPD, and other medical conditions involving breathing. |
| Air Quality Red | Unhealthy for all groups; index 151 to 200. Everyone may experience some ill effects, sensitive groups more so. |
Watches are put in place after advisories. They indicate that conditions have worsened but the occurrence, timing, and location is still unknown. The idea is to provide those in the area enough lead time so that plans can be set in motion if necessary. Under a watch, it would be prudent to check the emergency kit, make sure the batteries in the flashlight work, charge the cell phone, refill medications, pick up items in the yard, and take other steps so that if conditions continue to worsen the person is ready to take the next steps necessary to protect property and people. Again, some categories may vary by area, but the basics still apply. Watches are issued before the exact location of where the storm or event is going is known. Watch areas are larger than warning areas because storms are difficult to predict, and it is always better for more, rather than fewer, people to be prepared.
Wind advisories, watches, and warnings are significant not just for boats, but for vehicles crossing larger bridges. Some bridges even close to tractor trailers and certain trucks depending on wind strength. Strong winds can topple a light truck, an empty tractor trailer, or other vehicles depending on configuration.
| Type of Weather | Nature of Watch |
| Winter Storm Watch | Indicates the possibility of significant and hazardous winter weather within forty-eight hours. Significant and hazardous winter weather is five inches or more of snow/sleet within twelve hours, or seven inches within twenty-four hours and/or enough ice accumulation to damage trees or power lines and/or a life threatening or damaging combination of snow/ice accumulation with wind. |
| Freeze Watch | The potential for significant, widespread freezing temperatures exists within the next twenty-four to thirty-six hours. Issued during spring at the start of growing season and autumn at the end of growing season. |
| High Wind Watch | Issued when sustained winds of 40 miles per hour for an hour or more, or gusts 58 miles per hour for any duration are possible. |
| Hurricane Watch | Issued when a tropical cyclone containing winds of 64 knots or 74 miles per hour or higher poses a threat within the next forty-eight hours. It may be accompanied by storm surge or coastal or river flooding. |
| Severe Thunderstorm Watch | Issued when severe thunderstorms are possible in or near the watch area. A severe thunderstorm is one with winds of 58 miles per hour or higher and/or hail one inch in diameter or larger. |
| Tornado Watch | Issued when severe thunderstorms and tornadoes are possible in or near the watch area. A tornado is a violently rotating column of air, usually hanging from a cumulonimbus cloud with the circulation reaching the ground. |
| Tropical Storm Watch | Issued when a tropical cyclone containing winds of 34 to 63 knots or 39 to 73 miles per hour or higher poses a threat within forty-eight hours. May be accompanied by storm surge or coastal or river flooding. Tropical storms often graduate into hurricanes. |
| Coastal Flood Watch | Issued when moderate to major coastal flooding is possible. This flooding potentially poses a serious risk to life and property. Varies by region; this is for the Tidal Potomac River and Chesapeake Bay. |
| Flash Flood Watch | Issued when conditions are favorable for a flash flood. A flash flood is a rapid and extreme flow of high water into a normally dry area or a rapid water level rise in a stream or creek above normal flood levels. It begins within six hours of the causative event (such as rainfall or dam failure) and the time threshold varies by area. |
| River Flood Watch | Issued when flooding is possible at one or more points along a river. |
| Excessive Heat Watch | Issued when the potential exists for the heat index to reach or exceed 110 within the next twenty-four to forty-eight hours. |
| Fire Weather Watch | Geared towards fire officials and firefighters. Warns of potentially dangerous fire weather conditions within the next twenty-four to thirty-six hours. The following criteria are required: surface relative humidity less than 30 percent for Virginia and Maryland and 25 percent for West Virginia; sustained surface winds of 20 miles per hour or greater; and ten hour fuel moisture less than 8 percent for Virginia or less than or equal to 8 percent for Maryland and West Virginia. |
| Air Quality Purple | Index is between 201 to 300. A health alert would be triggered to indicate everyone may experience serious health effects. Air is very unhealthy. |
Warnings indicate that a hazardous weather event is occurring, imminent, or has a high probability of occurring. A lot depends on the nature of the weather; a tornado warning indicates that a tornado is on the ground in the area and people should take cover immediately, whereas a hurricane warning means that within a certain amount of time the area will be hit by a hurricane. Warnings always indicate conditions that pose a threat to life or property. Steps should be taken to protect both. Cities and local government may require evacuation of certain areas, schools may send children home or shelter them in place, and churches and other sites may start preparing to become emergency shelters. The steps taken depend on the nature of the weather.
| Type of Weather | Nature of Warning |
| Blizzard Warning | Indicates that within the next twelve to eighteen hours snow and/or blowing snow reducing visibility to one-third mile or less for three hours or longer and sustained winds of 35 miles per hour or greater, or frequent gusts of 35 miles per hour are occurring or expected. There is no temperature requirement. |
| Winter Storm Warning | Indicates a significant combination of hazardous winter weather is occurring or imminent. Significant/hazardous weather is a combination of five inches or more of snow/sleet within twelve hours or seven inches or more of snow/sleet within twenty-four hours and/or enough ice accumulation to cause damage to trees or power lines and/or a life threatening or damaging combination of snow and/or ice accumulation with wind. This varies with location. |
| Ice Storm Warning | Ice accumulation of one-fourth inch or more. |
| Freeze Warning | Significant, widespread freezing temperatures are expected. Similar to advisories and watches is issued in the spring at the start of growing season and in the fall at the end of growing season. Growing seasons vary by location. |
| Wind Chill Warning | Wind chills of -20F or lower are expected. Varies by area. |
| High Wind Warning | Sustained winds of 40 miles per hour or higher are expected for one hour or more or gusts of 58 miles per hour for any duration are expected. |
| Hurricane Warning | Issued when sustained winds of 64 knots or 74 miles per hour or higher associated with a tropical cyclone are expected in thirty-six hours or less. Storm surge and coastal or river flooding may accompany the winds. The warning can stay in effect when dangerously high water, or a combination of high water and exceptionally high waves, continue even though winds have fallen below hurricane force. |
| Extreme Wind Warning | Issues for surface winds of 100 knots or 115 miles per hour or greater associated with non-convective, downslope, derecho (not associated with a tornado), or sustained hurricane winds are expected to occur within one hour. Convection is the movement of heat and moisture through the air; downslope is a thermally driven wind directed down a mountain slope, usually at night; and derecho is a widespread and usually fast moving windstorm associated with convection. |
| Gale Warning | These warnings are issued when one or both of the following are expected to begin within thirty-six hours, and not directly associated with a tropical cyclone: sustained winds of 34 to 47 knots or frequent gusts for two hours or more between 34 and 47 knots. Varies by area; this is for the Tidal Potomac River and Chesapeake Bay. |
| Storm Warning | Storms are stronger than gales. The following are expected to begin within thirty-six hours: sustained winds 48 to 64 knots or frequent gusts over two hours or more of 48 to 64 knots or greater. Varies by area; this is for the Tidal Potomac River and Chesapeake Bay. |
| Special Marine Warning | A unique marine warning not covered by existing marine warnings and warns of potentially hazardous conditions of short duration, up to two hours, producing sustained marine convective winds (showers/thunderstorms) or associated gusts 34 knots or greater and/or hail three quarters of an inch or more and/or waterspouts. A waterspout is a tornado over water. |
| Severe Thunderstorm Warning | Severe thunderstorms are occurring or imminent. A severe thunderstorm consists of winds of 58 miles per hour or higher and/or hail one inch in diameter or larger. |
| Tornado Warning | Indicates a tornado is imminent. Shelter should be sought immediately. |
| Coastal Flood Warning | Moderate to major coastal flooding is occurring or imminent. The flooding poses a serious risk to life and property. |
| Flash Flood Warning | Flash flooding is imminent or occurring. |
| River Flood Warning | Issued when river flooding is imminent or occurring at one or more points along a river. |
| Excessive Heat Warning | Issued when the heat index value is expected to reach or exceed 110 within the next twelve to twenty-four hours. Like a watch, may be issued for lower temperatures if it occurs early in the season or over multiple days. |
| Red Flag Warning | Used to alert fire officials and firefighters of potentially dangerous fire weather conditions within the next twelve to twenty-four hours. Three criteria must be met: surface relative humidity less than 30 percent for Virginia and Maryland, 25 percent for West Virginia and sustained surface winds of 20 miles per hour and ten hour fuel moisture less than 8 percent for Virginia, less than or equal to 8 percent for Maryland and West Virginia. Varies by area. |
| Air Quality Maroon | Hazardous air that triggers health warning of emergency conditions that affect the entire population. |
Because thunderstorms can cause significant damage and lead to hurricanes, thunderstorms have their own threat rating level. The level ranges from 0 to 5, with 0 being no threat of thunderstorms and 5 being the threat of severe storms including tornadoes or derechos for an extended period of time.
| 0 | No severe thunderstorms expected; general or non-severe thunderstorms. Lighting and flooding can be expected with any thunderstorm. |
| 1 | Marginal risk – isolated severe storms that are either short-lived, cover a small area, or limited in intensity. |
| 2 | Slight risk – scattered severe storms – area of short-lived organized severe storms but not widespread with varying levels of intensity. Some isolated intense storms may be possible. |
| 3 | Enhanced risk – numerous severe storms possible covering a wider area, lasting longer with the potential for some intense storms. |
| 4 | Moderate risk – widespread severe weather likely with numerous severe thunderstorms and several tornadoes. Storms will be widespread. Supercells producing intense tornadoes or very large hail, or an intense squall line with widespread damaging winds. A squall line is a narrow band of high winds and storms forming along or ahead of a cold front. |
| 5 | High risk – widespread severe weather expected from thunderstorms producing numerous and intense long-tracked tornadoes or derechos. This level is used when widespread areas of severe weather with extreme severe tornadoes or very damaging winds are expected. |
The creation and definition of these terms are established by The National Weather Service, which provides a glossary. The National Weather Service has field offices throughout the country that watch concerns in a particular area. Each region has a number of local forecast offices that handle forecasts for a smaller area such as Baltimore/Washington, Cleveland, Buffalo, and other areas. They are divided alphabetically. This is also where the advisories, watches, and warnings are generated as the local offices watch the weather for the local area. A listing of regional and field offices can be found here. Link to the Nation Weather Service here and the National Oceanic and Atmospheric Administration here.
These terms, however, are just the beginning. Once a watch or warning has been issued, it is helpful if insureds have a plan and know what steps to take to protect valuables and themselves. Further information can be found in the following articles: Disaster Compendium Part I; Disaster Compendium Part II; Disaster Compendium Part III; Disaster Compendium Part IV.
But this is just the beginning. Not everything has a warning system since some things happen without any warning such as earthquakes. Volcanoes are also random, while there may be some earthquakes preceding an eruption the timing and actual magnitude are impossible to accurately predict. Once the loss happens, coverage comes into play. An insured may need coverage provided only by endorsements or specialty policies. The compendiums mentioned earlier provide some basic information on coverages.
Other terms
Beyond the advisory, watch and warning terms, there are others that are equally important. Some may not yet be official, but are new descriptors being used as storms change. One is "walking storm", which is a very slow moving storm, which tends to drop significant amounts of rain on an area. Hurricane Sally has been called a walking storm because it was moving at just 2 miles an hour, the pace of a slow stroll, meaning that it could yield 30 inches of rain in some areas because of its slow progress.
Atmospheric River
An atmospheric river is a long, narrow river of condensed water vapor in the atmosphere that moves with the weather. A strong river can carry between 7.5 -25 times the flow of water that passes through the mouth of the Mississippi River. These rivers in the sky can be 300 miles wide, a mile deep and more than 1,000 miles long. While most are small, they can be massive and fast-moving, releasing large volumes of rain or snow. See A New Kind of Storm-Atmospheric River.
Bomb cyclone
A bomb cyclone is a storm that drops in atmospheric pressure very quickly, picking up more air and strength, and becoming stronger faster. To be considered a bomb cyclone the pressure must drop 24 millibars in twenty-four hours. The process of this rapid drop in pressure is called bombogenesis. These storms create large amounts of precipitation.
Weather whiplash
When an area experiences both extremes – extreme periods of dry followed by extreme periods of precipitation. Because of the extreme conditions, the extreme of wet that follows the extreme dry period cannot always restore the balance needed to return to normal conditions.
Storm surge
Is another very important term. Storm surge is the abnormal rise in the level of seawater during a storm that is above the normal level of the tide. The storm winds push the water onshore, often creating significant flooding.
Storm tide
Is not as familiar. It is the total observed level of seawater during a storm, and is the combination of the storm surge and the normal tide.
Originally published June 20, 2017
Updated 2/28/2020, 3/18/2021.