Watches, Warnings and Special Weather Statements Environment Canada's Meteorological Service is responsible for issuing all Canadian weather alerts using a variety of different technologies. Watches, Warnings and Special Weather Statements alert Canadians to a number of weather conditions that are occurring or are expected to occur, that could impact your safety or cause damage to property or the environment. Weather Alerts are issued for the following conditions: Depending on the severity of the weather expected or the onset time of the event, forecasters will issue different types of alerting bulletins. It is important that you are aware of the geographic region that you are in, so you can best assess your risk. The three types of weather alerts include: Special Weather Statements are issued for weather events that are unusual, cause general inconvenience or public concern and cannot adequately be described in a weather forecast. Special weather statements may be issued daily in summer to describe where thunderstorms are expected or occurring, or may reflect a warning in effect near our borders. These statements are updated as needed. Watches provides a “heads-up” that conditions are favourable for a possible summer or winter storm. This storm could affect your safety or at the least cause inconvenience, but at this time there is uncertainty about the track and strength of the system. A watch in the summer may be issued up to six hours before the event and in the case of winter events at least 12 to 24 hours in advance. Stay tuned for updates. This is the time to develop a plan in the event that the watch is upgraded to a warning, as conditions become more certain. Warnings alert you when severe weather is occurring or will occur. Activation of a specific warning takes into consideration local needs. Warnings are issued ideally when severe weather is expected to affect land-based communities within at least six to as much as 24 hours. Storms related to thunderstorms offer shorter advance notification and may be issued less than one hour in advance. Updated statements are reissued at least every six to eight hours or as needed, so you can stay up to date on the developing situation. More than one type of warning for a location can be in effect. Warning services are more limited or may not be available in remote or unpopulated areas. When a warning is issued it is time to put any plans into action. Weather Alerts used in Canada include: A Severe Thunderstorm Watch is issued when conditions are likely for the development of thunderstorms, some of which may become severe thunderstorms with large hail, heavy rain, deadly lightning or damaging winds and possibly tornadoes within the areas and times specified in the watch. You should use this time to secure loose objects, shelter animals, ensure family members or co-workers are prepared to take action and listen carefully for an updated weather report. This is the time to develop a plan. A Severe Thunderstorm Warning is issued when a severe storm has developed, producing one or more of the following conditions: flooding rain, destructive winds with gusts greater that 90 km/h, hail of at least 10 to 20 mm in diameter or intense lightning. Severe thunderstorms may also produce tornadoes. The storm’s expected motion and developments will be given in the warning. If you are in the area specified, take shelter. Safety Tip: Use the lightning safety 30-30 Rule...if you count less than 30 seconds between the lightning flash and the sound of thunder, it is time to take shelter. Wait 30 minutes after the last clap of thunder to resume activities. A Tornado Watch is issued when severe thunderstorms have developed and there is the possibility of one or more tornadoes developing within the areas and times specified in the watch. Be prepared to take action if a warning is issued. A Tornado Warning is issued when one or more tornadoes are occurring in the area specified or detected on Doppler radar. The expected motion, development and duration will be given in the warning. Find appropriate shelter. Safety Tip: Remember that severe thunderstorms sometimes produce tornadoes with little or no warning. Treat all funnel clouds and tornadoes seriously. If you see a funnel approaching or large hail is falling you should immediately take shelter. Other “twister sisters” - cold-core funnels, funnel clouds, landspouts and waterspouts. These tornadic type events are often not associated with severe thunderstorms and are therefore difficult to forecast. They can appear with little or no warning. Funnel clouds that form out of large cumulus clouds or very weak thunderstorms normally do not have the energy to reach the ground. If they do briefly touch down they can be destructive over a small area. A Tornado Watch is issued if more funnel clouds are expected. Cold-core funnels are true funnel clouds by appearance, but will not lead to a damaging tornado. They are usually brief and thin, and often occur under the rain-free base of weak storms or large cumulus clouds during relatively cool, moist weather from spring to fall. These funnel clouds are commonly seen in the Prairies, in summer, during spells of cool, windy and unsettled weather. When cold air funnels are reported a Tornado Watch is issued. Landspouts are a weak tornado type seen under small summer storms or large, growing cumulus clouds. It is like a cold-air funnel that has touched down and can cause brief, usually minor, damage. They normally move slowly and can last for minutes. Landspouts occur in most parts of Canada. They don't always have a full condensation funnel and are sometimes only made visible by the dust they stir up. A Tornado Watch is issued if there is a reasonable probability of more landspouts developing. The waterspout is another weak tornado type. Like a landspout, it looks like a slender tornado, but occurs only over water in the same situations as cold-air funnels. They are occasionally seen near the coasts in the late summer and fall, but are more common in early fall over large lakes. A Tornado Watch or Tornado Warning will only be issued if a waterspout has the potential to move onshore. Special marine warnings are issued for waterspouts. Not all severe winds associated with thunderstorms are caused by tornadoes. Microbursts, macrobursts, downbursts, gustnadoes, squall lines, plough winds or derechoes are other labels given to damaging thunderstorm winds. Safety Tip: Remember damage, injury and death is often associated with flying projectiles and not just collapsing buildings or toppling trees Tropical Disturbances Tropical disturbances that become hurricanes all form over the Atlantic Ocean near the equator. Because they require very warm ocean temperatures the tropical storms and hurricanes that affect eastern North America generally form from June to November with a peak from August to October, when the water is at its warmest. A tropical cyclone will start as a disturbance. As the areas of thunderstorms develop rotational organization and the winds strengthen (20 knots to 37 km/h), it is upgraded to a tropical depression, tropical storm (winds reach 34 knots or 63 km/h) and finally a hurricane (winds reach 64 kts or 117 km/h). The five classes of hurricanes also reflect the increasing potential for damage. Each year on average three or four tropical storms or hurricanes pose a threat to eastern Canadian territorial waters or land. Depending on the path, its effects can be felt as far west as Quebec and Ontario or as far north as Nunavut. British Columbia is very rarely hit by eastern Pacific tropical cyclones. There are a number of alerting bulletins issued. They include: Hurricane Information Statements are issued when a tropical system threatens Canadian coastal waters or land. The statement includes public and marine impacts and warning summary, location and expected motion of the storm and technical discussion. This information is updated at least every six hours. Graphical Hurricane and Tropical Storm Track Information generally accompany the Information statement. A Tropical Storm Watch is issued when a tropical storm or tropical storm conditions pose a threat to coastal areas generally within 36 hours. A watch will generally cover a larger threat area than a warning, as the uncertainty on the track of the storm is greater. Now is the time to develop a plan. A Tropical Storm Warning is issued when winds of 63 to 117 kilometers per hour are expected. Warnings are not issued more than 24 hours in advance. Now is the time to put your plan into action. A Hurricane Watch is issued when a hurricane approaches the mainland and is considered a threat to coastal and inland regions. It gives people in the threatened area time to plan in the event that a warning is issued. This watch does not mean that a hurricane is definitely going to strike. It means that everyone in the area covered by the alert should be prepared to act quickly if warnings are issued that a hurricane will strike A Hurricane Warning is issued for coastal waters where winds greater than 117 km/h are expected. It may also include areas where storm surge or exceptionally high waves are predicted, even though winds may be less than hurricane force. Warnings are not issued more than 24 hours in advance. If the path is erratic or if the hurricane undergoes post tropical transition, the warning may only be issued a few hours in advance. Safety Tip : Forecast track error... 1-2-3 Rule 1-100 km error radius for 24-hour (one-day) forecast, 2-200 km radius error for 48-hour (two-day) forecast, 3-300 km error radius for 72-hour (three-day) forecast. Keep track of the storm’s progress through the Canadian Hurricane Centre advisories on radio, television or Environment Canada’s Web site. In addition to a hurricane watch or warning, additional warnings, such as a rainfall or wind warning, may be issued. A storm surge is a high and forceful dome of wind-driven ocean water that sweeps along the coastline near where the eye of a tropical or non-tropical storm makes landfall or passes close to the coast. A Storm Surge Warning is issued when a storm surge and/or high waves may result in significant flooding in coastal areas. Most hurricane-related deaths are from storm surge flooding. Storm surge flooding can occur over hundreds of kilometres of coastline and may extend inland several miles. Safety Tip: Know what the local tides are. High tides will significantly increase storm surge danger. Secure all boats and loose items on piers and boat houses. Leave low-lying beaches. High Heat and Humidity / Heat Wave / Humidex The elderly and individuals with pre-existing medical conditions are particularly vulnerable to heat stress. A heat alert system links mortality rates with weather data. A Humidex or High Heat and Humidity Special Weather Statement are issued when a threshold for temperature and humidity are exceeded. Special heat alerts or heat emergencies may be also issued by larger cities in addition to those issued by the weather centre. These alerts trigger a city to respond by distributing water to vulnerable sectors of the population, and to open air-conditioned facilities to the public for relief from the heat. A Environment Canada Humidex Advisory is issued when temperatures are expected to reach or exceed 30°C and the humidex values are expected to reach or exceed 40. Humidex values represent the effect which high humidity and high temperatures have on the human body. The higher the humidex, the harder it is for perspiration to evaporate and cool the body. Safety Tip: When the temperature goes up, slow down. Drink plenty of water, your body needs it to keep cool. Adjust to activity gradually. It takes four to eight days for your body to acclimatize. Rain that is particularly heavy can cause traffic disruption, flooding and landslips, drainage and sewer problems and potential water contamination from runoff or in flooded areas. A Rainfall Warning is issued when heavy or prolonged rainfall is sufficient to cause local or widespread flooding or flash floods. Ensure drainage systems are clear of debris and operating. If travelling, give yourself extra time since sections of road may be flooded and driving conditions may be treacherous, especially in a low-lying or mountainous areas. Local rainfall thresholds vary considerably across Canada and reflect a potential for regional flooding. Some seasonal considerations are made for ground that is frozen or sodden. A rainfall warning is generally issued not more than 24 hours in advance and is not preceded by a watch. Safety Tip; 15 cm of swiftly moving water can knock people over. Four times that amount can sweep a car away. Never drive in a flooded roadway, it may be washed out. Heavy buildups of ice can bring down branches and trees as well as power and phone lines. This can result in disrupted power and communications for days. Even a small accumulation of ice many cause extreme risk to pedestrians and drivers. Farm animals might also have difficulty foraging for food. A Freezing Rain Warning is issued when you can expect slippery walking and driving conditions and possible damage to trees and overhead wires due to rain freezing on contact to form a coating of ice. Avoid travel. Generally warnings are issued when one to four hours or at least two mm of freezing rain is expected. Freezing rain warnings are not issued more than 24 hours in advance. During the winter they may be locally preceded by a Winter Storm Watch. Freezing drizzle is drizzle that freezes on impact when temperatures are below 0°C. While freezing drizzle does not accumulate at the same rate as freezing rain, it can glaze surfaces, which can cause slick sidewalks and hazardous conditions, especially on less-travelled roads. A Freezing Drizzle Warning or Special Weather Statement alerts you to the possibility of slippery walking and driving conditions due to freezing drizzle. Avoid unnecessary travel. Be prepared for slipperier than normal driving conditions. A freezing drizzle warning is issued when freezing drizzle is expected for seven hours or more in the Maritimes (eight hours or more in Newfoundland and Labrador) or significant accumulation is expected. When conditions are likely to rapidly cause the temperature to drop within two to three hours, from above the freezing mark to below the freezing mark, and the roads are wet roads from prior rain or wet snow during the time of rapid cooling, a Flash Freeze or Rapid Freeze Warning may be issued locally. Strong winds can occur on a small scale, from thunderstorms, Chinooks or local topography. Strong winds can also occur on a large scale, from tropical storms or low pressure systems and fronts. Strong winds and especially gusty winds can not only damage property, or make any loose item a dangerous projectile, but also can create unsafe traveling conditions and will affect your ability to safely steer your car. During the colder months high wind chills, blowing and drifting snow can create an additional hazard. With a Wind Warning expect inland winds blowing steadily at 60-65 km/h or more, or winds gusting to 90 km/h or more. Secure or put away loose objects such as outdoor furniture or garbage cans, put your car in the garage and bring livestock to shelter. Safety Tip: High wind in combination with heavy rain or snow can increase the risk of tree limb breakage or trees uprooting. Check your property for dead branches. Around 60 to 70 km/h you will have difficulty with balance and walking against the wind. Twigs and small branches blow off trees. Les Suêtes Wind Warning is issued for winds 65 km/h with gusts to 90. These winds occur over a specific area of the western Cape Breton highlands during certain unique meteorological conditions. Les Suêtes is an Acadian phrase used to describe very strong southeast winds that occur in an area along the western coast of Cape Breton Island. Local fisherman report that this wind can extend out to 15 to 25 kilometres offshore. Wreckhouse is located between Cape Ray and St Andrew's in Southwestern Newfoundland. This area is, at times, subject to extremely violent southeast winds, which have been strong enough to blow rail cars off their tracks. Safety Tip: Especially in mountainous regions, watch for highway signs posted that alert you to wind danger in that area. Special forecasts and alerting are provided for mariners on open water. Winds speeds are given in knots. Wind reflected warnings are as follows: Strong Wind Warning - Issued if winds of 20 to 33 knots are forecast (Consult the marine information page for a complete description of all marine warnings) A warning is generally issued only in the Prairie Provinces when blowing dust caused by high winds is expected to reduce visibility to one kilometre or less for one hour or more. Dust can impair breathing for people and animals, and make travel hazardous. Dust storms can develop suddenly in the form of an advancing dust wall that may be kilometres long and hundreds of metres high. The most severe dust storms occur in the summer and are often associated with downdrafts generated by thunderstorms or cold frontal passages. While the life span of the storm may last several hours, a local area that it passes over will feel the impact for only 15 to 30 minutes. Dust Storm Warnings are not issued more than 12 hours in advance. Safety Tip: If you must go out, breathe through a wet face cloth. A blizzard is produced by a combination of strong winds and falling or loose snow on the ground which severely reduces visibilities in blowing snow. Blizzards create very dangerous conditions which make travel dangerous due to whiteout conditions and drifting snow. Hazardous wind chills become an additional hazard for anyone stranded. A Blizzard Warning is issued when winds of 40 km/h or more, are expected to cause widespread reductions in visibilities to less than one kilometre, due to blowing snow, for at least four to six hours. Warnings are generally issued 12 to 24 hours in advance. In some regions a blizzard warning may be preceded by a Winter Storm Watch. Blizzard conditions generally do not last more than six to 12 hours, but have been known to last four to six days. Often blizzard conditions will develop suddenly after the passage of a storm system. Safety Tip: Be prepared to encounter sudden lower visibilities when travelling through open areas away from wind breaks such as trees and buildings. When blowing snow is expected to reduce visibility to less than 1 km (<5/8 mile) but not necessarily meet the blizzard definition for duration and temperature, or if it is more local in nature, a Blowing Snow Warning or Special Weather Statement may be issued. Heavy snowfall can paralyze a city and leave commuters stranded. It can collapse power lines, knock down trees and in the mountains it can lead to avalanches. The amount of snow which has fallen in the previous days or even the first snow after a long dry spell in winter can create additional safety concerns. A Snowfall Warning is issued when hazardous amounts are expected to fall over a 12- or 24-hour period. These amounts vary across the country due to topographical and climatic considerations. They range from five cm in 24 hours for parts of southwestern BC to 15, 20 and even 25 cm in 24 hours elsewhere. Snowfall warnings are not issued more than 12 to 24 hours in advance and in some regions a Winter Storm Watch may give advance notification to a warning. A Special Weather Statement may be issued for lesser amounts in special circumstances. Safety Tip: remember that a thin layer of snow offers less traction than a few centimetres. In the lees of larger lakes in the fall or early winter, cold air picks up moisture off the open water and becomes unstable. Snow squalls or lake effect snow squalls may make it look like it is snowing out of a blue sky. As the air moves inland, snow squalls can dump heavy snow over a small area in a few hours. As the winds shifts, snowfall moves over other areas. Lake effect snow bands can be very persistent and last as long as 48 hours. The combination of heavy snow and gusty winds can cause localized blizzard-like conditions. A frontal snow squall can occur with the passage of a cold front. It is marked by a sudden onset of strong winds with heavy snow that reduce visibilities to near zero in blowing snow. A Snow Squall Warning will be issued to the lee of the Great Lakes when 15 cm or more of snow is expected to fall within 12 hours, or the visibility is likely to be near zero for at least four hours because of falling and blowing snow. A Frontal Squall Warning may be issued when blizzard-like conditions are expected to develop in the vicinity of a cold front. When more than one winter hazard is expected to occur, then a winter storm alert may be issued. Be aware of the potential for heavy snow, reduced visibilities, strong winds, freezing rain or extreme wind chill. A Winter Storm Watch will alert you to the potential of hazardous conditions. It will precede a variety of potential warnings and may be issued up to 48 to 60 hours in advance. A Winter Storm Warning will alert you that a combination of hazardous winter conditions are occurring or expected to develop shortly. A warning is normally not issued more than 12 to 14 hours in advance. A more generic Weather Warningmay be issued when a progression or combination of weather hazards are expected to occur as a storm moves through an area. A Special Weather Statement may be issued to highlight widespread fog that is giving reduced visibilities less than one km or to explain hazy skies, reduced visibilities due to forest fire smoke or blowing dust in the winter. Safety Tip: The onset of low visibilities in fog or smoke while driving may be very abrupt. Reduce your speed. A loss of visual references may distort your ability to determine how fast you are driving. In Canada, injuries from frostbite and fatalities from hypothermia are not uncommon. Wind chill can play a major role in these health hazards. Wind chill is the cooling sensation caused by the combined effect of temperature and wind. The wind chill index compares the way your skin feels like under certain wind and temperature combinations, to a temperature on a calm day. At values of -25, wind chill units begin to appear in your forecasts. When a Wind Chill Warning is issued, expect very cold temperatures combining with wind to create outdoor conditions hazardous to human activity. Wind chill warning criteria vary across the country, ranging from -55 in some arctic regions to -30 in southwestern Ontario. Warnings will be issued when the winds are expected to be at least 15 km/h and these extreme wind chills will persist for at least three hours. Safety Tip: There is a risk of frostbite in less than 10 minutes when the wind chill is near -40. When temperatures are expected to fall dramatically within 24 hours from above normal or near seasonal temperatures to very cold temperatures a Cold Wave Warning is issued in some parts of the country. A few times during the winter very cold arctic air breaks from the interior mainland of British Columbia and spills out through mountain gaps and fjords with bitter gale force winds. An arctic outflow from Howe Sound and into the Strait of Georgia is locally called a Squamish. In addition to unusually cold temperatures and gale force winds they can bring heavy snowfall and severe icing to offshore vessels. An Arctic Outflow Warning is based on a combination of wind speed and temperatures which produce wind chills of at least -20 for at least six hours. A Frost Warning is issued or referenced in the public forecast only when air temperatures are expected to fall to near freezing or below during the local growing season, as early as April 15th to October 15th in southern British Columbia and for shorter periods elsewhere in Canada. A frost warning would normally be issued when forecast air temperature is +2°C or below. The UV index is included in Environment Canada's weather forecasts whenever it is expected to reach 3 (moderate category) or more. Remember that the amount of UV you receive depends on both the strength of the sun's rays (UV Index) and the amount of time you spend in the sun. Special alerts are not issued. Poor air quality, especially fine particles and ground-level ozone, affects respiratory health and contributes to hundreds of premature deaths each year in Canada. It also impairs visibility and adversely affects materials and the natural environment. Smog is the most visible form of air pollution and is of particular concern in several of Canada's major urban areas (the Lower Fraser Valley, the Windsor-Quebec Corridor and the Southern Atlantic Region) during spring and summer. Air quality forecasts are issued daily across the country. The program works in partnership with the various provinces. In addition to the forecast, when standards are exceeded an Air Quality Advisory (BC), Smog Watch and Smog Advisory (Ont), Air Quality and Health Advisory (Atlantic) or Smog Warning (Quebec) is issued by the provinces. Different technologies - How do we communicate? The media are our primary means of reaching Canadians. They are a vital to ensuring that Canadians receive weather information and alerts in timely manner. They generally receive information through their local wire services or through Environment Canada’s internet media portal. The current weather forecasts and alerts can be accessed by the general public via Environment Canada’s Weatheradio continually broadcast VHF frequencies, the internet via the Meteorological Service Weatheroffice Web site, local automated telephone recordings or a 1-900 / 1-888 user-pay phone service that enables callers to access meteorologists from 5am to 6pm daily. Public access to historical weather and climate data from the MSC’s national climatological database can also be accessed through the Weatheroffice Web site . 
Created :
2002-08-22
Modified :
2006-07-12
Reviewed :
2002-12-18
Url of this page : http://www.msc.ec.gc.ca
/cd/brochures/warning_e.cfm
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