Avalanche Forecast

Issued: Apr 19th, 2018 4:41PM

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

cgarritty, Avalanche Canada

Cariboos.

Clues to mountain hazards are currently quite apparent on the surface. Tune in to overhead hazards, moist snow, and lingering wind slabs to allow for safe travel on Friday.

Summary

Confidence

Moderate -

Weather Forecast

Friday: Cloudy with isolated flurries and a trace of new snow, increasing overnight. Moderate to strong south winds. Freezing level to 1800 metres with alpine high temperatures around -3. Weak overnight cooling.Saturday: Cloudy with continuing scattered flurries and about 5 cm of new snow. Moderate to strong west winds. Freezing level to 1600 metres with alpine high temperatures around -4.Sunday: Mainly sunny. Light west winds. Freezing level to 1700 metres with alpine high temperatures around -5.

Avalanche Summary

No new avalanches were reported in the Cariboos on Wednesday, but reports from the North Columbias included observations of numerous natural wind slab release from size 1-2 on north through east aspects in the alpine. A skier triggered size 2 storm slab resulted in a near miss. Another recent very large (size 3.5) storm slab was observed to have released on a large, wind-loaded alpine feature. Reports from Tuesday included observations of several large (size 2) wind slabs that released naturally as a result of recent strong winds.Observations were hindered by poor visibility on Monday.Reports from Sunday and late last week showed a pattern of heightened cornice failure activity, with several cornice releases triggering large persistent slabs and wind slabs.Looking forward, continuing warm temperatures will be maintaining elevated chances of loose wet avalanche and cornice activity before another round of light snowfall introduces new surface instabilities over Friday night and Saturday.

Snowpack Summary

About 50 cm of rapidly settling storm snow covers a supportive crust on all aspects to at least 2100 m (and possibly higher on south aspects).Within this storm snow there are several different crusts with the shallowest of these (down about 25 cm) becoming a gradually diminishing concern as warm temperatures have promote settlement and bonding in the upper snowpack. Recently formed wind slabs on the surface at higher elevations are expected to be on a similar stabilizing trend.With warm daytime temperatures and poor overnight recovery of cold temperatures, there remains some lingering concern around reactivity at the mid-March persistent weak layer in the alpine where it is found 100 to 150 cm below the surface. This buried crust/surface hoar interface may still be capable of producing large avalanches if triggered with a heavy load, such as a cornice collapse.Deeper persistent weak layers from December and January may be starting to become reactive to very large triggers. A recent cornice collapse is believe to have initiated a slab release on an early season layer, 300 cm deep.

Problems

Loose Wet

Sustained warm temperatures are expected to maintain an elevated likelihood of loose wet avalanches in steeper terrain, especially at lower elevations. 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: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Cornices

Several large cornice failures have been reported in recent days. Large cornice collapses have the potential to trigger a deep weak layer near the base of the snowpack, which would result in a very large and destructive avalanche.

Give cornices a wide berth when traveling on or below ridges.Cornices weaken with sun and daytime heating. Minimize your exposure to large cornices overhead.

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

2 - 3.5

Wind Slabs

Lingering wind slabs from 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. Light new snow and increasing winds will begin to build new slabs on Friday.

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

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