Avalanche Forecast

Issued: Jan 8th, 2018 12:15PM

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

Bill Phipps, VIAC

Vancouver Island.

Summary

Confidence

Moderate- few alpine but good treeline and below treeline observations, weather forecast models mainly in agreement.

Travel/Terrain Advice

Avoid wind loaded slopes and features with north-west aspects that gather wind transported snow. New snow will increase the size/hazard that exists on the wind slabs created Sunday, so keep an eye on actual new snow amounts Monday-Wednesday. Loose snow sloughs can entrain additional snow adding to hazard. Avoid slopes that will magnify loose avalanches like gullies and bowls below steep terrain.

Past Weather

Rain up into the alpine Friday saturated the upper snow pack. Cooling temps Saturday brought new snow to elevations above 1000 m (2-10cm). Sunday 5-15 cm of new snow fell in the mountains with larger amounts in the west and south regions and less to the north. Strong (up to 70k mph) winds from the south-east accompanied the new snowfall.

Avalanche Summary

Small size 1-1.5 loose dry avalanches were reported with control work on Mt Washington Sunday, running on the skier compacted crust down approximately 10cm. Intentional ski cuts in open treeline terrain elsewhere produced small to very small wind slab avalanches up to size 1 on the lee of wind loaded rolls and features running on the new crust created by last Fridays rain event.

Snowpack Description

Surface - Variable surface conditions from moderate density new snow in wind sheltered zones to exposed crusts on wind stripped alpine and treeline ridges. Upper - New snow, blown by Sundays winds, has formed firm wind slabs on lee (north-west facing) features in the alpine and exposed treeline. Approx 1-15cm on new snow fell on the forecast area Sunday, capping the newly formed rain crust from Fridays rain event. The bond between the new snow and crust was poor in test on Sunday on significantly steep terrain.Mid - The new snow and crust buried on Jan 7th is now bridging and limiting concerns surrounding the mid Dec and mid Nov crusts. The moist mid snowpack seams very stable.Lower - Well settled.

Weather Forecast

Warm temps and slightly high freezing levels Monday morning will begin to drop by mid day bringing new moist snow. Tuesday-Wednesday will see increasing snowfall and very low freezing levels and temps. This new snow is very welcome to our lower than seasonal snowpack and should provide excellent conditions and powder. Mon - 10-20 cm of new snow. Winds light to moderate south to south east trending to north west. Freezing levels of 1400-800 m Tues - 2-6 cm of snow. Winds light to moderate south west-north west. Freezing levels of 550-950 m Wed - 0-15 cm of new snow. Winds light west to south east. Freezing levels of 175-850 m

Problems

Loose Dry

New snow through the forecast period will almost certainly produce loose dry snow avalanches on all aspects in zones of steep unsupported terrain at treeline elevations and above. These avalanches could be up to size 2.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Certain

Expected Size

1 - 5

Wind Slabs

Sundays new snow combined with high winds from the south-south east created easily triggered avalanches with human activity in isolated loaded terrain features up to size 1.5. These slabs will see additional load with warm temps and moderate new snow Monday, making them even more touchy to triggers (up to size 2). New snow Tuesday and Wednesday will come in with only light to moderate wind, once again adding additional load onto these wind loaded pockets. These wind slabs will exist in the alpine and open exposed zones at treeline (like ridge top features and bowls) and will mainly be on north to west aspects.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Valid until: Jan 10th, 2018 6:00PM