Avalanche Forecast

Issued: Apr 21st, 2018 3:46PM

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

cgarritty, Avalanche Canada

Cariboos.

A lack of field observations means that current forecasts for the region are based on only limited weather observations. Gather information as you travel and watch for the destabilizing influence of the sun.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

Sunday: A mix of sun and cloud. Light west winds. Freezing level to 1600 metres with alpine high temperatures around -6.Monday: Mainly sunny. Light southeast winds. Freezing level to 2100 metres and climbing overnight. Alpine high temperatures around 0.Tuesday: Mainly sunny. Light to moderate south winds. Freezing level to 2500 metres with alpine high temperatures around +2.

Avalanche Summary

Reports from Thursday included more evidence of the recent natural avalanche cycle described below, with several additional recent storm and wind slab releases to size 2.5 observed. Sun and wind were identified as prominent triggers.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. Tuesday's reports included observations of several large (size 2) wind slabs that released naturally as a result of recent strong winds.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, sunshine and warming temperatures are expected to initiate a natural avalanche cycle limited to the new snow. The same warming may also cause natural cornice collapses.

Snowpack Summary

About 5-10 cm of new snow has accumulated above a melt freeze crust found on the previous surface on all but north aspects above about 2200 metres. Below it, about 50 cm of settled storm snow covers another supportive crust which shares similar distribution to the upper crust.Within this storm snow there are several different crusts with the shallowest of these (down about 25 cm) now a limited concern after warm temperatures have promoted settlement and bonding in the upper snowpack. 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 deep This buried crust/surface hoar layer 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

Wind Slabs

Light new snow and strong winds have likely form thin new wind slabs in the lee of exposed terrain. Slabs are likely to remain reactive over the near term and reactivity is likely to increase with daytime warming on Sunday.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 1.5

Cornices

Several large cornice failures have been reported in the past week. 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

Loose Wet

Daytime warming and sun exposure will promote natural loose wet avalanche activity on Sunday - especially around steep sun-exposed terrain.

Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.Minimize exposure when the solar radiation is strong, especially if snow is moist or wet.

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

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 1.5

Valid until: Apr 22nd, 2018 2:00PM