Avalanche Forecast

Issued: Apr 19th, 2018 4:41PM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Loose Wet, Cornices and Wind Slabs.

cgarritty, Avalanche Canada

South Columbia.

Clues to mountain hazards are currently quite apparent on the surface. Tune in to overhead hazards, moist snow, and lingering wind slabs as you travel and watch for the destabilizing effect of sun exposure.

Summary

Confidence

Moderate -

Weather Forecast

Friday: Mainly cloudy with isolated flurries and a trace of new snow, increasing overnight. Light southwest winds becoming strong at ridgetop. Freezing level to 2100 metres with alpine high temperatures around -1 to 0.Saturday: Cloudy with continuing flurries bringing4-10 cm of new snow. Moderate to strong west winds. Freezing level to 1700 metres with alpine high temperatures around -4.Sunday: A mix of sun and cloud. Light northwest winds. Freezing level to 1800 metres with alpine high temperatures around -3.

Avalanche Summary

Reports from Wednesday included an observation of a natural size 2 cornice release from a north aspect in the north of the region. Numerous natural loose wet avalanches were also observed on sun-exposed aspects in the Monashees.Tuesday's reports showed numerous small (size 1) storm slabs releasing both remotely and with ski cutting. Crown fractures were in the 35-40 cm range and activity was observed at all elevations and on all but west aspects.On Sunday, warm temperatures initiated widespread natural storm slab and loose wet avalanche activity on all aspects below 2300 m.In addition to heightened storm slab activity following regular snowfalls, observations from late last week also showed a pattern of heightened cornice failure activity. Reports of 'bus sized' blocks found in debris as well as a suspected cornice-triggered size 4 wind slab release in the adjacent North Columbias and Glacier National Park should keep these looming giants top of mind.Looking forward, continued warm temperatures will be maintaining elevated chances of loose wet avalanche and cornice activity before another round of snowfall introduces new surface instabilities over Friday night and Saturday.

Snowpack Summary

About 70-100 cm of rapidly settling storm snow overlies a crust on all aspects to at least 2300 m (and possibly higher on south-facing slopes). Within the upper snowpack there are now a few different crusts with the shallowest of these (down 30-50 cm) becoming a diminishing concern as warm temperatures promote settlement and bonding in the upper snowpack.With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains some lingering concern around the mid-March persistent weak layer in the alpine where it is found 80 to 120 cm below the surface. This buried crust/surface hoar interface was widely reactive but is likely trending towards dormancy. It should be kept in the back of our minds for its capability to produce large avalanches should it be triggered with a heavy load such as a snowmobile or cornice collapse.Deeper persistent weak layers from December and January are considered dormant at this time.

Problems

Loose Wet

Weak overnight cooling and continued warm temperatures will continue to promote loose wet avalanches in steeper terrain. Loose snow releases may occur naturally or with a human trigger.

Manage your sluff and be extra cautious where long slopes allow for more snow entrainment.Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.Use extra caution on slopes if the snow is moist or wet.

Aspects: North, North East, East, South East, South.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Cornices

Large cornice failures have been reported in the past week and cornices continue to weaken under prolonged warming. Cornice releases may have enough force to trigger a deep weak layer and cause a very large and destructive avalanche.

Cornices become weak with daytime heating. Minimize your overhead exposure.Give cornices a wide berth when travelling on or below ridges.

Aspects: North, North East, East, South East.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Wind Slabs

Lingering wind slabs formed after the last snowfall my still be reactive to human triggering in isolated areas. The main concern is for steep wind-loaded slopes near ridge crests.

Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

1 - 2.5

Valid until: Apr 20th, 2018 2:00PM