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Weather vancouver bc canada 14 day forecast definition meaning synonymVANCOUVER - Definition and synonyms of Vancouver in the English dictionary - Weather Forecast 14 days for nearby cities
Immediately following is 'Your Long Range Forecast' giving conditions for the next 4 days in southern Ontario. The new programming is a continuation throughout the day of Good Morning Toronto. Airs at and minutes after each hour. This is a four- to five-minute newscast highlighting weather stories and environmental issues and includes packaged news reports. The Weather Network then won for its two-part news series on weather and black history.
The Weather Network also won a World Medal from the NY Festivals International TV Broadcasting Awards for a story on a blind woman learning to sail who uses her other senses to determine changes in wind patterns and potential storms.
It won the same award again in for a story on a man and his seeing-eye dog trying to adapt to a harsh New Brunswick winter. In addition to its web site, The Weather Network has an e-mail service called WeatherDirect, that sends weather forecasts via e-mail. There is also an e-mail service for pollen conditions and road conditions.
TWN has a small desktop application that can be downloaded free called WeatherEye, which displays current weather conditions, short term and long term forecasts on the desktop. The service will provide alerts to participating media outlets, who will then relay the information to their viewers and listeners. Pelmorex first issued a proposal for All Channel Alert in , but was denied, due to efforts at the time by local stations, as well as developments by Environment Canada to establish a similar system of its own.
The network has always been for its excessive use of advertising through commercials and forecasts and some weather segments e. The same problem also occurs with the U. In the past, there was little to no advertising. Currently, local forecasts are sponsored using static logos during and after forecasts. The station has also been criticized for putting more focus over the weather in Southern Ontario than the rest of Canada during its national segments. During a technical difficulty, it often shows a repeated version of a local forecast.
Every three or so months, the two morning time slots 5 a. Here is the list of on-air presenters who had helped to launch TWN's Mississauga era. All translations of weathernow. A windows pop-into of information full-content of Sensagent triggered by double-clicking any word on your webpage.
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Find out more. Jump to: navigation , search. For other uses, see TWN disambiguation. Map from The Weather Network, 29 May Pelmorex Radio Network. Pierre L. CP24 Southern Ontario. SKY TG Webmaster Solution Alexandria A windows pop-into of information full-content of Sensagent triggered by double-clicking any word on your webpage. Try here or get the code SensagentBox With a SensagentBox , visitors to your site can access reliable information on over 5 million pages provided by Sensagent.
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My account login registration. Pelmorex Media Inc. Morrissette - The Weather Network. Contents 1 History 1. This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. August Suzanne Leonard. Sheryl Plouffe. Chris Murphy. Anne-Marie Sweeney. Chris St. Natalie Thomas. Kelly Noseworthy. Shelley Steeves. CTV Toronto. Debra Arbec — Gary Archibald — Candice Batista — Tarah Black Now Tarah Schwartz.
Tim Bolen Host on Rogers Television , Toronto. Environment Canada meteorologist. News Writer CP24 in Toronto. Carla Collins. A sledder investigates a slab avalanche triggered when a critical amount of new snow overloaded a weaker layer. Critical loading happens when new precipitation or windblown snow overloads a slab sitting on a weak layer.
A slab that has reached its critical load may avalanche naturally or with a light trigger. The suggested threshold for identifying critical loading is 30 cm or more of new snow, or significant wind, or rain during the hour period prior to and up to the end of your day. Cross-loading is the result of wind transporting snow across a slope.
During cross-loading, snow is picked up from the windward side of ribs and outcrops and is deposited in lee pockets. Cross-loading commonly contributes to wind slab formation. The crown is the uppermost part of the fracture of a slab avalanche, where the slab breaks away from the snowpack overhead. It connects to the flanks of the avalanche on either side and sits perpendicular to the bed surface of the avalanche.
The height of the crown is generally used when measuring the dimensions of an avalanche. Crusts are hard layers of snow usually created by liquid freezing on or near the snow surface. They can also result from strong winds. Crusts can act as a firm bed surface for slab avalanches after they are buried in the snowpack. The presence of a weak layer on the crust can contribute to the likelihood of slab avalanches. If a crust is strong enough to support the weight of a person or machine, it may reduce the chance of triggering the weak layers beneath it.
The Dangerator guides you through a two-step process of combining weather data and field observations to assess whether the danger is moderate, considerable or high. The Dangerator does not include low or extreme avalanche danger. Deep persistent slabs are an avalanche problem defined by the presence of a weak layer, usually at or near the base of the snowpack, that resists bonding to an overlying slab over an extended time period.
This weak layer is normally a product of snow grain metamorphism within the snowpack rather than the accumulation of new snow or formation of surface hoar on the snow surface. Once formed, a deep persistent slab can last for an extended period, sometimes throughout the entire season. They can survive numerous avalanche cycles and are inherently difficult to forecast.
Managing this problem involves avoiding large avalanche paths and avoiding terrain where the problem exists. Traveling in dense trees is a good choice when avalanche danger is elevated - if there's enough room to maneouver. Dense trees are forested areas where the canopies of the trees are touching. Dense trees shelter the snow from the effects of wind and sunlight, they modify the snowpack by shedding snow think tree bombs , and they inhibit the growth of surface hoar.
In some cases, dense trees also work to anchor the snowpack in place, limiting the potential for a slab to dislodge from the snowpack. Traveling in dense trees can be a good choice in periods of elevated avalanche danger. Depth hoar is an advanced, generally larger and weaker form of faceted snow crystal usually found near the bottom of the snowpack.
Like basal facets, depth hoar exists as a persistent weak layer in the snowpack and is frequently associated with deep persistent slab avalanche problems. Depth hoar crystals show visible striping known as striations and in later stages often form hollow cup-like shapes. The dew point is the temperature to which air must be cooled to become saturated with water vapour.
When the dew point is reached and the temperature is below freezing, water vapour is deposited on surfaces like the ground as frost.
This is how surface hoar forms on the snowpack in the mountains. Surface hoar is notoriously problematic and frequently becomes a persistent weak layer once it is buried in the snowpack. Layers in the snowpack are always changing.
Sometimes they are gaining strength, other times they become weaker. Like the name suggests, a layer becoming dormant is not necessarily a permanent change. The chance of a dormant layer waking up is a serious consideration during storms when load on the snowpack is increasing , during times of rapid or prolonged warming, and especially if these kinds of changes are preceded by a period where the snowpack has weakened, such as a cold snap.
Explosives are an effective and widely adopted tool in numerous public and industrial avalanche safety programs around the world. Explosives act as a large trigger that can be placed in a precise location without exposing workers to avalanche hazards. They are used to remove snow from slopes before it can build up enough to create very large avalanches. Avalanche occurrences, whether natural or artificial, offer observers high quality information about local avalanche problems.
For this reason explosive-triggered avalanches figure prominently in public avalanche forecasts. Photo: A large avalanche is triggered using explosives. From the Canadian Avalanche Association. The extended column test is a snowpack test that is similar to the compression test but uses a much wider column of snow that gives an observer a better indication of fracture propagation.
It involves applying an incremental load to the column and then monitoring it to see the point at which it fractures, and how far the fracture spreads along the weak layer.
Extreme is the highest of five levels on the avalanche danger scale. Natural and human-triggered avalanches are certain; large to very large avalanches are expected in many areas; and all avalanche terrain should be avoided. Extreme avalanche danger is used rarely in avalanche forecasts.
Conditions such as avalanches running beyond the existing bounds of their path, avalanches running into forested terrain, avalanches running across valleys and up the other side, or avalanches impacting simple terrain are possibilities under extreme danger.
Faceted snow refers to snow grains within the snowpack that have transformed into larger, angular grains. Facets have weak bonds with neighbouring snow grains. It is often referred to as sugary snow. When present, faceted snow frequently exists as a persistent weak layer in the snowpack and it is commonly associated with persistent slab avalanche problems. A strong temperature gradient is the condition that promotes the faceting process.
For this reason facets often form at the base of the snowpack, near the surface of the snowpack, near crusts, in shallow snowpack areas, and in areas where rocks or trees perforate the snowpack. Avalanche Canada avalanche technician Ben Hawkins holds up a 3 cm thick crust found with overlying facets in his snowpit. The combination of facets and crust in close proximity is a common feature of snowpacks that contain crusts.
Facets can grow either above or below the crust. Facets commonly grow above crusts. For example, when rain wets the snow and cold snow falls on top of it, it produces a very strong temperature gradient from the wet layer to the snow surface.
Once the wet layer freezes and forms a crust, facets can form above the crust and act as a weak layer while the crust acts as a hard sliding surface below. This increases the likelihood of avalanches. Facets can also grow below a crust as the crust inhibits the movement of water vapour through the snowpack.
As the flow of water vapour halts near a crust, vapour is deposited as ice on nearby snow grains, creating facets. This is less problematic than facets forming above a crust, but avalanches can still happen if the crust slides along with an overlying slab.
The fracture that releases a slab avalanche spreads along a weak snowpack layer called the failure plane. The bed surface usually lies immediately below the failure plane. The term flank refers to the side of an avalanche. Two flanks, one on each side, are connected by the crown, or upper fracture line, which runs across the top. The line that forms the outer extent of the slab fracture of a slab avalanche. Fracture lines outline the top of the start zone and often part of the flanks of a slab avalanche after it has released.
They often connect a line between likely trigger points and locations of heightened strain on the snowpack, such as convexities, as well as thinner or perforated snowpack areas. The upper part of a fracture line is commonly referred to as a crown. Under normal atmospheric conditions, temperature decreases with altitude. The red line indicates the freezing level, where the temperature equals 0 C.
The freezing level is the altitude at which the air temperature reaches 0 C zero degrees Celsius. In the atmosphere, temperature typically decreases with height so that the temperature is above 0 C at elevations below the freezing level, and below 0 C at elevations above the freezing level.
However, warm air associated with Pacific frontal systems frequently invades British Columbia during winter, causing warm air to overrun cold arctic air settled in the valley bottoms.
This process creates a temperature inversion, where temperature increases with height, and can lead to an above freezing layer with multiple freezing levels. Rising freezing levels are generally synonymous with rising temperatures and a sign of a warming snowpack. Vertical slice through a frontal system; cold air and cold front left , warm sector middle , warm front and retreating cool air right.
Warm, moist air is forced to ascend at both fronts but does so more rapidly at the cold front. Frontal lift is one of four primary mechanisms of atmospheric lift.
Cold fronts, warm fronts, and occluded fronts all force air to rise, and if sufficient moisture is present, form clouds and precipitation. Glide cracks are openings in the snowpack that are created when a glide slab moves slowly down slope to expose the bed surface beneath the slab.
As the crack increases in size, they can indicate increasing instability of the slab. A glide slab is a cohesive slab of snow, often consisting of the entire snowpack, that lacks significant support of friction from the bed surface beneath it. Grass slopes, smooth rock slabs, or areas exposed to geothermal heat are common areas for glide slabs to occur.
Glide slabs are often visible by the presence of glide cracks, which form as the slab begins to tear away from the surrounding snowpack. When the strength of the slab is finally overcome, it releases as an avalanche. A hand shear test is a snowpack test that allows you to test the strength of a shallow weak layer.
It involves isolating a small column of snow with your pole and then pulling on it with your hand. It is a quick way to test how a surface snow layer is bonded with the underlying snowpack.
Hand shear tests work well to test out shallow or new snow instabilities, but are not useful for testing deeper weak layers. Hangfire is a term used to describe unstable snow that is left on a slope above the fracture line of a slab avalanche. Hangfire is a serious concern when coordinating avalanche rescue because the potential exists for it to release on the rescuers. If hangfire threatens a rescue—and resources allow—the best practice is to station someone in a safe spot where they can monitor the hangfire and warn other rescuers if a second avalanche releases.
As well. A hard slab consists of dense wind-packed snow or old snow that has hardened after a long period of settlement. Hard slabs are usually more than a few days old and can support the weight of a person or machine. Hard slabs are more difficult to trigger than soft slabs, but they tend to propagate much farther and therefore have greater destructive potential.
Hard slabs are also more likely to fracture above a person or machine, rather than below, making the likelihood of becoming involved in the resulting avalanche much higher. High is the second highest level on the avalanche danger scale. During periods of high danger, avalanche conditions are very dangerous and travel in avalanche terrain is not recommended. Natural avalanches are likely and human-triggered avalanches are very likely.
Large avalanches are expected in many areas or very large avalanches in specific areas. Under high danger, all avalanche terrain should be avoided. Use extra caution when travelling in simple terrain and stick to very mellow slopes or dense trees that are free of overhead hazard.
A high pressure system over western Canada creates widespread sunshine. Surface winds are generally light, except in this weather map example where tightly packed isobars lines of equal pressure near the coastal fjords result in strong outflow winds. High pressure systems generally result in clearer skies and reduced precipitation. An area of relatively high atmospheric pressure surrounded on all sides by lower pressure is referred to as a high.
An elongated region of high pressure extending from a high is called a ridge. It is common for surface hoar and facets to form on the snow surface during periods of high pressure, particularly those that last several days. These become a weak layer when they get buried by subsequent storms and can be responsible for persistent slab problems. Two ski tracks on the left of the photo show where skiers entered the slope and triggered an avalanche.
These are avalanches triggered by a person or machine. An avalanche is considered to be machine-triggered if the person triggering is on a snowmobile or other motorized vehicle. An inclinometer or clinometer is a tool that measures the angle of a slope. Because most avalanches take place on slopes between degrees, an inclinometer is a valuable tool in determining whether or not a slope is steep enough to slide.
Isothermal snow is snow that is at the same temperature throughout a given depth range. In practice, the term isothermal is most often used to describe a snowpack that has reached its melting point, 0 Celsius, throughout its depth. As a snowpack reaches its melting point, the bonds between snow grains transform from ice to water, resulting in a loss of cohesion throughout the snowpack. Loose wet avalanches and wet slab avalanches often result from surface layers reaching 0 degrees.
As deeper layers of the snowpack begin to melt, larger avalanches become possible. The term leeward, or lee, refers to slopes that are oriented away from the wind. If winds are strong enough, snow from windward slopes can be redistributed or blown to leeward areas, causing them to become loaded. Wind slabs often form on lee aspects as a result of this wind transport. A loose snow avalanche consisting of wet snow.
It was triggered by the sun warming the snow near the rocks. Loose snow avalanches are avalanches that start from a point on the snow surface, gather mass progressively in a fan-like shape, and are composed of snow that lacks cohesion. They differ from slab avalanches in that they do not have a fracture line or release at a failure plane within the snowpack.
Instead, they are usually confined to surface layers and have relatively narrow propagation. In very steep terrain, loose snow avalanches are more prevalent than slab avalanches. Loose snow avalanches are described as loose wet or loose dry avalanches depending on whether they are composed of wet or moist snow, or dry snow. Small loose snow avalanches are often referred to as sluffs.
Since loose snow avalanches start from a point and fan out, they are also called point releases. Loose dry avalanches are a type of loose snow avalanche composed of dry snow. These types of avalanches are most likely to occur - either naturally or with a human trigger - when surface snow layers are composed of deep, low density snow. Loose wet avalanches are a type of loose snow avalanche composed of wet or moist snow.
They occur when surface snow loses strength due to melting. Because of their high density, wet loose avalanches tend to contain greater mass and are often more difficult to fight against than loose dry avalanches.
In periods of prolonged melt or rainfall, loose wet avalanches can become very large and destructive. These events are most common later in the winter and spring, and are associated with warm temperatures, strong solar radiation, and rain. Check out this video of a powerful loose wet avalanche that had enough mass to shake trees as it went past. The lowest of five levels on the avalanche danger scale. Under low danger, avalanche conditions are considered generally safe but avalanches can still be triggered on isolated features and in extreme terrain.
Natural and human-triggered avalanches are considered unlikely. Watch for any signs of instability and avoid obvious trigger points such as shallow rocky start zones. Surface air flows outwards diverges from an area of high pressure H and spirals counterclockwise into a low pressure system L. Converging surface air is forced to rise, cooling as it does so. If sufficient moisture is present, cloud formation occurs followed by subsequent precipitation.
Low pressure systems generate cloudy skies, precipitation, and, over time, drastic changes in temperature and wind. Air flows from areas of high pressure to areas of low pressure, spiraling inwards and upwards in a counterclockwise manner, resulting in atmospheric lift.
An area of relatively low atmospheric pressure surrounded on all sides by higher pressure is referred to as a low. An elongated area of low pressure extending from a low is called a trough.
It also requires a patient and diligent mindset, shown through the willingness to avoid suspect slopes - and adjacent areas that could be impacted by a high consequence avalanche - for extended periods of time. Snow metamorphism refers to the change of snow crystals over time. Snow crystals begin to metamorphose from the instant they begin to fall. After new snow is added to the snowpack, the form and size of snow crystals now labeled snow grains changes continuously.
As snow grains change, layers within the snowpack strengthen and weaken. One type of snow metamorphism is the result of sublimation and deposition. These are physical processes that transform ice to water vapour without a liquid phase and vice versa. In the snowpack we see this as ice from grain surfaces transforming into water vapour which is then deposited as ice on other grain surfaces. Sublimation and deposition processes are driven by the temperature gradient of a given snowpack layer.
Together, temperature gradient and the movement of water vapour determine whether rounding or faceting processes will dominate within the snowpack. Melt-freeze is another type of metamorphism that changes the composition of snow grains through melting and refreezing, rather than through sublimation and deposition. Moderate is the second of five levels on the avalanche danger scale.
Under moderate danger there is heightened avalanche conditions on specific terrain features. Features of concern should be identified and terrain and snow should be evaluated carefully.
Natural avalanches are unlikely and human-triggered avalanches are possible. Small avalanches can happen in specific areas and large avalanches in isolated areas. Pay careful attention to the avalanche problems in the forecast to avoid slopes where avalanches may be triggered. An avalanche is said to be natural if the trigger is not a result of the actions of a person or animal, or from another avalanche on an adjacent slope.
Natural triggers include:. A vertical slice through a mature weather system showing how the faster-moving cold air has pinched off the warm air that was once at the surface cold occlusion depicted. An occluded front occurs when the faster, trailing cold front of a low pressure system catches up to the slower moving warm front.
This process lifts the wedge of warm air originally ahead of the cold front, cutting it off from the ground, and also lifts the warm front itself. A temperature difference across the occluded front is still observed, but it is smaller cold to cool air instead of cold to warm air. It is represented on international weather maps by a purple line with alternating purple triangles and semicircles pointing in the direction the front is traveling in.
On Canadian surface weather maps, the occluded front is not typically analyzed. Instead, the elevated front, known as a TROWAL tro ugh of w arm air al oft , where the cold front has lifted the warm front off the ground, is drawn. The heaviest precipitation occurs at the point where the cold front has caught up to the warm front.
Here, the temperature contrasts are greatest and lift is amplified. Open trees describes forested areas where the tree canopy is open, or where the forest cover is uneven or patchy.
Open trees do not anchor the snowpack in place in the same way that dense trees do. Instead, their perforation of the snowpack forms a network of weak points that are more likely to aid the propagation of a fracture line than to hold a slab in place. Open trees in avalanche terrain may also be indicative of historical avalanche activity.
It can involve numerous personnel and extensive resources such as helicopters and avalanche rescue dogs, and can last several days. Orographic lift causes precipitation to fall on the windward side of mountains and ranges shown here on the left , while the leeward side right remains dry.
Arrows transitioning from red to blue, and vice versa, indicate cooling of rising air and warming of descending air. Orographic lift takes place when a moving mass of air encounters a physical barrier such as a mountain range and is forced upwards. The rising air cools, condenses and forms clouds. On the leeward side of mountains downwind , air descends , warms, becomes drier, and creates an area of lower precipitation, commonly called a rain shadow. Since the predominant wind direction in the mid-latitudes of North America is from west to east, orographic lift is a key component of precipitation patterns and snowpack depth.
Consequently, western-facing windward slopes experience higher annual precipitation accumulations than eastern-facing lee slopes. Pacific frontal systems will also wring out a larger percentage of their moisture content over the Coast Mountains, with less moisture available to fall over the Columbia and Rocky Mountain ranges.
The sledder in the photo above is exposed to overhead hazard from the overhanging cornices above, some of which have recently fallen across her intended path. Overhead hazard refers to an avalanche slope or other hazard such as cornice or loose rock that threatens the area below it.
When traveling in avalanche terrain, it is important to maintain awareness of overhead hazards and the places they threaten. Overnight freeze, re-freeze, or overnight recovery refers to the snowpack returning to a frozen state after a period of daytime warming.
Re-freezing can occur as a result of below zero air temperatures, radiative cooling of the snowpack, or both. Overnight re-freeze is an important consideration during spring and summer travel in avalanche terrain because the refrozen snowpack is much more stable than a snowpack that remains moist or wet overnight. Good overnight recovery of the snowpack ensures relatively safe conditions from the early morning until the heat of the day begins to melt the snowpack once again.
During periods of prolonged warming when there is no overnight freeze , it is wise to avoid avalanche terrain. A persistent slab is an avalanche problem that is defined by a slab formed over a persistent weak layer.
New snow that accumulates and consolidates over a persistent weak layer is normally first labeled a storm slab until the persistent nature of the weak layer becomes apparent over time. Persistent slabs are most likely to result in dangerous human-triggered avalanches when the weak layer is buried cm below the snow surface. When the layer is buried more than one metre deep, it usually becomes harder to trigger, but can still result in a very large, destructive avalanche.
It also requires a patient and diligent mindset, shown through the willingness to avoid suspect slopes for extended periods of time. An avalanche technician points to a buried persistent weak layer that failed during her snowpack test. A persistent weak layer is a weak layer in the snowpack that resists forming a strong bond to neighbouring grains in the snowpack over an extended time period.
They can be composed of surface hoar, facets, or depth hoar. Pinpoint search is the act of using a probe to pinpoint the location of a victim buried in an avalanche. It follows a successful transceiver search to the point where the victim was buried. Probing is done in a spiral or square, starting at the point where the strongest transceiver signal is found and spiraling outwards in 25 cm increments until a strike is made. Each one has a different impact on snowpack structure.
Precipitation of any kind adds load to the snowpack and stresses the weak layers within it. Critical loading of weak layers present in the snowpack can occur during rain or heavy snowfall. The video illustrates how precipitation particles fall to the ground as snow, sleet ice pellets , freezing rain, or rain depending on the vertical temperature structure in the atmosphere. If the air temperature rises above and remains above zero, rain occurs.
When a mid layer of warm air overrides cooler, valley bottom air, ice pellets or freezing rain form, the deciding factor being the depth of the cold air in the valley bottoms. Video by The Comet Program. A probe line consists of a group of searchers lined up in a row to look for someone buried in an avalanche, each person with an avalanche probe.
Probe lines are normally employed when a transceiver search is either unsuccessful or not possible. Propagation refers to the spreading of a fracture in the snowpack. Slab avalanches occur when a fracture propagates along a weak layer on a slope that is steep enough to avalanche.
The fracture then propagates through the slab as it separates and slides away from the surrounding snowpack. The farther these fractures propagate, the larger the resulting avalanche will be. For this reason, propagation propensity , or the tendency for a fracture to spread, is an important indication of the destructive potential of a slab.
The extended column test and propagation saw test are ways to test the propagation propensity of a slab over a weak layer. The propagation saw test is a form of snowpack test that involves drawing the back edge of a snow saw up the length of a known weak layer in a column of snow. During the test, the weak layer is monitored and the test is halted the moment it begins to independently propagate the fracture being initiated by the saw.
The results of the test give a point observation of a weak layer's tendency to propagate a fracture once it has been initiated. Caption: A map of southeastern British Columbia, showing avalanche forecast regions outlined in blue and major highways in yellow. The hour precipitation forecast is shown in coloured shading.
Quantitative Precipitation Forecast QPF refers to the quantity or amount of precipitation usually conveyed in millimetres of water forecast to accumulate at a given location over a specified period of time. Common time intervals are one hour, three hours, 12 hours, or per storm event. Remote-triggered avalanches are avalanches that occur away from the point where they are triggered. They happen when a slab fractures the weak layer below it but does not produce an avalanche at the site of the fracture.
Instead, the fracture propagates along the weak layer until it reaches a portion of the slab that rests on a slope that is sufficiently steep to avalanche. Remote triggered avalanches are a strong sign of an unstable snowpack. If you have observed or caused a remote triggered avalanche, a good course of action would be to avoid avalanche terrain.
Video: Doug Latimer and Jordy Shepherd demonstrate the strike team conveyor shovelling method. Rescue digging refers to the digging and extrication phase of an avalanche rescue. Digging for a person buried in avalanche debris is physically demanding and often takes longer than the search, so an efficient approach to recovering a burial subject is an important means of maximizing the chances of a positive outcome.
The strike team method is a systematic rescue digging technique for multiple shovelers and one of the best approaches for rescue digging. To employ this technique:. Reverse loading occurs when winds blow counter to the prevailing wind direction, transporting snow to normally wind-scoured slopes. Reverse loading creates irregular and often complicated patterns of wind effect in exposed areas.
For example, in an area where winds normally blow from west to east, the snow would be blown from west-facing windward slopes onto east-facing leeward slopes. If a system brought winds from the east, the situation would be reversed, and snow would be deposited on slopes that are normally wind-scoured. A rib is a vertical ridge of snow that runs down a slope.
On slopes that are cross-loaded by the wind, the leeward side of ribs will be loaded with snow, making them likely to contain wind slab problems. A skier walks up along a ridgetop. She will have to be cautious to avoid getting close to the cornices, which can be a major hazard when they break.
Ridgecrest and ridgetop are terms used interchangeably to describe terrain at or near the top of a ridge. Ridgetop terrain is significant for a number of reasons:. Rime is a deposit of ice from super-cooled water droplets.
It can accumulate on the windward side of rocks, trees, and structures; and on falling crystals of snow. When snow crystals cannot be recognized because of rime, the grains are called graupel. Rounded snow refers to snow grains within the snowpack that have transformed into small, increasingly spherical grains. Rounded snow grains are packed tightly in the snowpack and bond well to each other, creating a snowpack or layer that is increasingly strong. A weak temperature gradient is the condition that promotes the rounding process.
Dense, tightly packed snow; and small snow grains are other contributing factors. A rutschblock test is a form of snowpack test that involves applying the weight of a person in increments to a large column of snow. Like the compression test, the rutschblock test gives a point observation of weak layer strength as well as fracture propagation propensity.
One advantage of the rutschblock test is its unique and impactful approximation of an avalanche involvement through its use of a human trigger and a large slab of snow. The use of safe spots is an important part of safe travel in avalanche terrain. Safe spots are also targeted when performing a ski cut. Sastrugi are convoluted formations of snow scoured out of the snow surface by wind.
Sastrugi are often found in areas where a significant depth of loose, wind-transportable snow is exposed to a strong wind event. Satellite communications devices offer a range of communication capabilities for users outside of areas covered by cellular service. These devices have a number of valuable uses for outside communication while in the backcountry, and especially for emergency response. Satellite communication devices may require an open line-of-sight to a specific point in the sky, or may be subject to operating windows determined by the movement of satellites.
Terrain that obstructs line-of-sight to the sky may limit the operation of satellite communications devices. Elevations and temperatures of weather stations A at sea level , B at 1,m above sea level , and C at 1,m above sea level are shown.
The mathematics take into consideration station altitude, station temperature, and minor instrumentation corrections. Sea level pressure is a calculated value determined by measuring the actual pressure at a given weather station and correcting it for altitude.
Atmospheric pressure is measured by surface weather stations across the globe. Since the elevation of these stations can vary significantly from the coast of British Columbia to the Rocky Mountains, station pressure the actual pressure measured at the station is converted to sea level pressure the pressure that would exist if that station was at sea level. Doing so simplifies the pressure analysis, allowing meteorologists to compare pressure at different locations. It also includes several assumptions, such as how temperature changes with altitude, which at times, can lead to incorrect values.
Erroneous data, if identified, can be ignored or smoothed over while doing a hand analysis of isobars on a weather map. Self-arrest is the act of stopping oneself from moving downslope during a sliding fall.
Self-arrest is one way of staying out of an avalanche after being caught. It can be achieved by anchoring oneself to a set of ski poles or ice axe while using body weight to drive their tips into the snow surface, or by hanging onto a tree or other object not caught in the flow. Settlement refers to the process that consolidates the snowpack and diminishes its depth over time. Settlement is synonymous with strengthening of snow, but it can result in both stable and unstable snowpack structure.
A shallow rocky start zone is an area of the snowpack where avalanches are more likely to be triggered. Areas where the snowpack is shallow and perforated by rocks are known to promote the formation of weak, faceted snow. Weak layers present in a shallow snowpack are also normally closer to the snow surface than in deeper snowpack areas. This places these layers closer to the triggering forces of a person or machine traveling on the snow above.
Avalanches triggered in shallow snowpack areas often have fracture lines that propagate to deeper snowpack areas. Shooting cracks are a sign of instability in the snowpack. They appear as cracks propagating outwards through the snowpack under the weight of a person or machine.
Shooting cracks are indicative of an unstable snowpack, often illustrating the transition of low density surface snow into a consolidating slab. If you see shooting tracks, you should avoid any slopes steep enough to avalanche.
These signs of instability indicate the snowpack structure is primed for human-triggering. The weight of a person or machine moving over the snow could be sufficient to release an avalanche.
If you notice any of these signs, the safest course of action is to avoid exposure to avalanche terrain. Stick to low angled, simple terrain, or routes that stay within densely forested terrain. Simple terrain is one of three levels of the Avalanche Terrain Exposure Scale.
It involves exposure to low angle or primarily forested terrain. Some forest openings may involve the runout zones of infrequent avalanche paths. Many options are available to reduce or eliminate exposure to avalanche danger. No glacier travel is required. Sintering, or pressure sintering , is the physical process of bond formation between grains in the snowpack.
It usually accompanies the rounding process. Sintering occurs when water vapour is deposited at the contact points between snow grains, forming necks. These necks then create strong bonds between grains, increasing the strength of the snow. Hardening or compaction from any mechanical disturbance such as boots, skis, snowmobiles, groomers, wind, and avalanches produces rapid sintering by breaking up large grains and bringing grains into close contact.
A ski cut, or slope cut or slope test, is an intentional attempt by a skier, snowboarder, or snowmobiler to safely trigger a small avalanche.
Ski cuts can be used to test the strength of weak layers in the upper snowpack, but they should only be attempted on small slopes where the consequences of an avalanche are limited. They are not useful for testing deeper weak layers. Effective ski cutting requires the skier or rider to enter the slope at or above the start zone and target the highest elevation, most likely trigger point before quickly traversing to a safe spot adjacent to the targeted slope. A ski cut that is executed poorly or in the wrong situation can be ineffective and dangerous.
Because the individual performing a ski cut is exposing themselves to possible avalanche involvement, their partners should observe the cut from a safe spot and be ready to perform a companion rescue if necessary.
A slab is one or more cohesive layers of snow overlying a comparatively weak snowpack layer. Slab formation takes place as low density new snow densifies and stiffens from the effects of settlement. Wind transport is another common contributor to slab formation.
The presence of a slab over a weak layer is one of the preconditions for a slab avalanche. Slab avalanches are formed when a slab of cohesive snow releases at a weak layer in the snowpack and slides over an underlying bed surface. They are the most dangerous types of avalanche for people as they can result in large amounts of snow rapidly breaking up around you, causing the ground to move as if someone just pulled the rug out from under your, and engulfing you before you have a chance to react.
Slab consolidation takes place as low density new snow densifies and stiffens from the effects of settlement and sintering. The chance for slab avalanches is introduced when slab consolidation occurs above a weak layer. The Slope Evaluation Card is the component of the Avaluator decision-making aid that deals with slope-scale decisions.
It employs a scoring system for avalanche conditions and terrain characteristics variables. After calculating the scores for each, the user applies these scores to a grid which suggests whether or not the slope in question is appropriate to travel on.
Slopes angles on which avalanches occur correspond to those that many skiers, snowboarders and sledders enjoy riding. The incline of a slope is a significant factor in whether or not it can avalanche. However, avalanches can happen on slopes as flat as 25 degrees and as steep as 60 degrees. The following guidelines for using slope incline to predict avalanche size and frequency have been developed from experience.
A minimum slope angle is required to initiate a slab fracture, however, a fracture may propagate to a flatter slope after an initial failure on a steeper slope has occurred. Traveling on lower-angled terrain and minimizing exposure to steep slopes is an effective way to limit exposure to avalanche terrain.
A sluff is synonymous with a loose snow avalanche but normally refers to a small release and is often associated with human triggering. Sluff is common while riding on steep slopes. While getting caught in sluff may be avoided with proper riding technique, sluffs can knock a person off their feet or machine, they can have high consequences if paired with a terrain trap, and can even bury a person if they gather enough mass.
Sluff management is the practice of anticipating sluff while skiing or riding and taking steps to avoid being caught in its flow. One of the most common forms of sluff management involves skiing short pitches and pulling over to safe spots to escape the flow of sluff while it passes.
This slope makes a good test slope, although any larger and the potential consequences would start to become significant. Small slopes are fairly short, generally only metres long, and are not exposed to terrain traps. They are considered low consequence terrain and are generally only able to produce small avalanches up to size one. By using them to test for instabilities, small slopes can be a good place to safely gain information about the presence and reactivity of avalanche problems in an area.
Caption: SLR has a huge impact on snow quality with higher values , or higher giving low density powder left , and more mild storms producing denser snow, better used for snow sculptures right. The snow-to-liquid ratio SLR is a measure used in weather forecasting to describe the water equivalent of forecast new snow. The most basic rule of thumb to follow would be to apply a SLR of i. In reality, SLRs vary from or commonly found in the westernmost coastal ranges to or more common in the Arctic and on eastern slopes of the Rockies.
Numerous weather products predict the quantitative precipitation forecast QPF, in mm , which requires forecasters and other users to convert to centimetres of snow by applying an appropriate SLR. Since SLR is linked to temperature, colder air tends to produce higher SLR or , resulting in lighter, fluffy powder snow, while warmer temperatures usually mean a lower SLR or and denser snow, which is excellent for making snowballs.
For example, if 10 mm of precipitation is forecast with mild temperatures, one might apply an SLR of Thus, the forecast would call for 10 cm mm of snow. If precipitation was occurring during a cold snap, one would apply a higher SLR of This means the same 10 mm of precipitation will create 20 cm mm of snow.
The general mountain ranges and snow climate zones of western Canada, with forecast regions outlined overtop. The idea of a snow climate is a way of grouping geographical areas according to broad trends in weather and snowpack composition. Three snow climates have generally been used to categorize different regions in Canada:. A maritime snow climate is found in mountain ranges closest to the ocean. In western Canada, it is found in the Coast Mountains and Cascades.
In eastern Canada, it is found in coastal Quebec and Newfoundland. Maritime snowpack regions are characterized by frequent intense storms, deep snowpacks, and warm weather.
Avalanche danger in maritime snowpack regions is typically connected with storm events where snowfall rapidly accumulates and forms unstable storm slabs or wind slabs. A maritime snowpack often stabilizes within one or two days of a storm. Persistent weak layers are less common in a maritime snowpack, but they are not rare. The perception they are rare may in fact increase the chance of someone getting caught by surprise by a persistent slab avalanche.
A continental snow climate exists in mountains a long distance from the ocean, such as the Rocky Mountains. A continental snow climate is characterized by cold weather and thin snow cover from relatively infrequent storms. These conditions frequently lead to the formation of persistent weak layers such as facets, depth hoar, and surface hoar.
As a result, avalanche danger in a continental snow climate can rise sharply with only light snowfall and often persists long after storms. The snowpack in a transitional snow climate shares characteristics of both maritime and continental snowpacks. The depth of a transitional snowpack can be similar to a coastal snowpack, but it is generally composed of less dense snow.
Weather conditions are often conducive to the formation of persistent weak layers that can last for weeks or even months. The vertical temperature profile shows the transition of below freezing temperatures aloft to mild valley bottom air freezing level. Precipitation phase is overlaid and illustrates how snow changes to wet snow and then to rain delineating the snow level once temperatures rise above 0 C.
The snow level is the altitude at which precipitation changes from snow to rain. How far below the freezing level it is located depends on the amount of cooling that takes place due to sublimation and melting. If the air mass is dry in the low levels, falling snow will sublimate change from frozen water to water vapour and cool the atmosphere. The snow level will quickly plummet from near the freezing level to several hundred metres below. If the atmosphere is moist, little cooling from sublimation will occur but melting snow which also cools the atmosphere still occurs.
The harder it is precipitating, the more melting occurs, leading to greater cooling and lowering of the snow level.
A general rule of thumb to determine snow level is to subtract m from the freezing level, but depending on the atmospheric conditions, snow level may be substantially lower. A variety of standardized snowpack tests have been developed to aid in assessing snowpack structure and stability.
Common examples include:. Avalanche forecasts that discuss weak layer reactivity and slab propagation propensity in relation to snowpack tests normally refer to these tests. Test results are generally more concerning and indicate greater instability when classified as 'sudden' or 'easy' and less so when labeled 'resistant' or 'hard'.
It is important to not put too much faith in a single test result. The safest way to interpret the results is to use them to potentially rule out skiing a slope, and to never use the result to rule-in skiing a slope. For training in proper application and interpretation of these tests in the field, please consult an avalanche professional or attend a recognized training course.
Soft slabs are composed of light, low-density, recent snow. Soft slabs form as this snow settles and consolidates over time or with redistribution by wind.
Soft slab avalanches tend to be triggered easily by the weight of a person or machine. Solar warming is warming caused by radiation from the sun. As a result of solar warming, east to west aspects often see increased rates of snowpack settlement and more frequent melting of snow at the surface. This can result in accelerated slab formation, the creation of surface crusts, and wet loose avalanches. Even when air temperatures are below freezing, solar radiation can bring snow to its melting point.
When air temperatures are above zero, solar radiation can greatly increase snow melt. The exposure of slopes to the sun changes over each day and throughout winter according to their incline and aspect.
Slopes that saw little solar warming early in winter experience substantially more in spring as the sun shines on the snow for longer periods and from higher up.
Slopes receiving direct sunlight are most affected by solar warming. Spot probing is conducted if a transceiver search is unsuccessful or not an option. It is done in likely burial areas around trees, rocks, and depressions in the terrain. Effective spot probing requires rapid, continuous, and methodical probing of these areas. The more holes poked in the snow, the more likely the searcher will be to find the person buried.
A 3D representation of a stationary front with the wedge of stationary cold air on the left and warm air on the right. The vertical red arrows indicate lift near the frontal zone that may produce clouds and precipitation.
A stationary front is an interface between two air masses that are not moving or moving very slowly. Surface winds blowing parallel to the front can help it remain in place for longer. Weather along the frontal zone depends on the two air masses at play.
If both air masses are relatively dry, cloud cover will be scattered with little or no precipitation. If one or both air masses is sufficiently moist, widespread cloud cover with intermittent to steady light precipitation can be expected. A stationary front is represented on weather maps by alternating blue and red line segments, with blue triangles that point towards warm air and red semicircles that point towards cold air. This avalanche triggered by a sledder stepped down to ground on the left side of the slide while the right side failed on a shallower weak layer and bed surface.
A slab avalanche is said to step down if the motion of the initial slab causes deeper layers to fail, resulting in a larger avalanche than the one that initially released and a second bed surface deeper in the snowpack.
A step in the bed surface may be visible, or in many cases, may be scrubbed away by the motion of the slab release. A storm slab is one or more layers of recent storm snow that has consolidated into a slab above a weak layer. Storm slab distribution is generally much wider than that of wind slabs due to the slab forming as a result of snowfall rather than wind effect.
It is one of eight avalanche problems identified in avalanche forecasts. Management of storm slab problems involves paying close attention to slope angle and slope size, as the widespread nature of the problem means that it tends to affect most slopes where avalanches can occur.
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