Avalanche Forecast

Purcells

Date issued

Apr 17, 2018 - 4:45 PM

Valid until

Apr 18, 2018 - 2:00 PM

Prepared by

cgarritty

The severity of avalanche problems varies with new snow depths across the region. Expect a trend toward sunshine and warming to destabilize both loose snow and recently formed slabs over the course of each day.

Regular season
Tuesday - April 17, 2018
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Wednesday - April 18, 2018
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Thursday - April 19, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Avalanche Problem 1: Loose Wet

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

Forecast warming temperatures and sunshine are likely to destabilize surface snow and initiate loose wet avalanche activity - especially on steep south facing features. The likelihood of cornice failures also increases with sun and warming.

Travel and Terrain Advice
  • Cornices become weak with daytime heating, give them a wide berth when traveling above or below.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

Avalanche Problem 2: Storm Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

Storm slabs and wind slabs from the last round of snowfall may remain reactive to human triggering on Tuesday. The greatest caution is needed around steep or convex terrain as well as sun-affected slopes where slabs formed over a recent crust.

Travel and Terrain Advice
  • Use extra caution around cross-loaded terrain features.
  • Be especially careful around wind loaded pockets near ridge crests and roll-overs.

Avalanche Summary

Poor visibility limited observations of avalanche activity on Monday.

Sunday there was a report of a near miss for skiers who triggered a size 2 wind slab on a north aspect at treeline in the northern part of the region. While in the northwestern part of the region saw a warming-induced, natural avalanche cycle up to size 3 on large alpine features in the recent storm snow.

Saturday, explosive control work in northern parts of the region produced several storm slab releases size 2-2.5 on predominantly treeline to alpine, west aspects with wide propagations up to 200 m. Ski cuts produced size 1-1.5 results on cross-loaded features.

On Friday, several skier-triggered, size 1.5 wind slab releases were reported on north aspects at 2300 m. A few solar-triggered storm slab releases (size 1.5) were also reported on steep, unsupported. west-facing features at 2200 m.

Snowpack Summary

About 20 cm on new snow overlies a crust on all aspects to at least 2000 m (and possibly higher on south-facing slopes), while 30-40 cm can be found at higher elevations (and up to 60 cm in some areas in the northwest of the region). Below 2200 m this new snow has thin surface crust, breaking down to moist or wet snow in the afternoons.

Within the upper snowpack there a now several buried crusts with only the mostly recently buried posing a concern as the uppermost layer of storm snow settles and bonds to it.

There is some lingering concern around the mid-March persistent weak layer in the alpine where it is found 50 to 90 cm below the surface. This buried crust/surface hoar interface is likely trending towards dormancy, but we need to keep it in the back of our minds as it is capable of producing large avalanches should it be triggered (think step-down from a surface avalanche or cornice collapse)

Deeper persistent weak layers from December and January are considered dormant at this time.

Weather Forecast

Wednesday: A mix of sun and cloud with isolated flurries and a trace of new snow. Light south winds. Freezing level rising to 1800 metres with alpine high temperatures around -5.

Thursday: A mix of sun and cloud. Light southwest winds. Freezing level rising to 2200 metres with alpine high temperatures around 0. Weak overnight cooling.

Friday: Mainly cloudy with flurries beginning in the evening and continuing overnight. Light southwest winds. Freezing level to 2300 metres with alpine high temperatures around +1.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

Avalanche Forecasts in your Inbox

Avalanche Canada has switched to an RSS feed for its daily forecasts. This is a much more flexible method that allows automatic delivery to your email inbox, or to an RSS reader of your choice.

What are RSS feeds?

RSS (Really Simple Syndication) is a popular standardized file format allowing up-to-date delivery of web-based content. RSS feeds enable you to receive content updates from websites, delivered to your email through an RSS aggregator (such as blogtrottr.com) or viewed through applications called RSS readers (such as feedly.com).

Set up an RSS feed for your email:

Select a RSS aggregator

  1. Purcells URL: http://www.avalanche.ca/api/forecasts/purcells.rss
  2. Copy the url and paste it into the appropriate field of your RSS aggregator.
  3. Fill in your email address.
  4. Voila! Watch the Avalanche Canada forecast roll into your inbox.

Forecast Disclaimer

Avalanche Canada's Public Avalanche Bulletin, and other information and services provided by Avalanche Canada, are intended for personal and recreational purposes only.

**THIS INFORMATION IS PROVIDED "AS IS" AND IN NO EVENT SHALL THE PROVIDERS BE LIABLE FOR ANY DAMAGES, INCLUDING, WITHOUT LIMITATION, DAMAGES RESULTING FROM DISCOMFORT, INJURY, OR DEATH, CLAIMS BY THIRD PARTIES OR FOR OTHER SIMILAR COSTS, OR ANY SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, ARISING OUT OF THE USE OF THE INFORMATION.**

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and uses the data in this bulletin with this always foremost in mind. The accuracy or reliability of the data is not guaranteed or warranted in any way and the Providers disclaim liability of any kind whatsoever, including, without limitation, liability for quality, performance, merchantability and fitness for a particular purpose arising out of the use, or inability to use the data.