Avalanche Forecast

Issued: Jan 23rd, 2019 5:31PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Deep Persistent Slabs and Wind Slabs.

cgarritty, Avalanche Canada

South Rockies.

A warming event will be testing the snowpack this week. The first impact will be felt on sun-exposed slopes on Thursday.

Summary

Confidence

Moderate -

Weather Forecast

Wednesday night: Decreasing cloud. Light northwest winds increasing to strong in the alpine.Thursday: A mix of sun and cloud. LightÂ to moderate southwest winds becoming strong northwest in the alpine. Alpine high temperatures around -9, increasing to around 0 overnight.Friday: A mix of sun and cloud. Strong northwest winds decreasing over the day. Alpine high temperatures around 0 with freezing levels reaching 2000 metres and increasing overnight.Saturday: Mainly sunny. Strong west winds. Alpine high temperatures around +5 as freezing levels rise to a possible 2900 metres.

Avalanche Summary

A size 1.5 natural wind slab avalanche was observed in steep terrain on Sunday. Skier traffic produced a few small (size 1) avalanches in the new snow on Thursday.The most recent reports of larger avalanches are from over a week ago, when warm temperatures stressed the deeper layers in the snowpack and produced a few size 2 avalanches.

Snowpack Summary

Strong winds have redistributed snow into thin winds slab in alpine lees and scoured windward areas. In more sheltered alpine terrain and between 1600-2000 m, 5-15 cm of recent snow overlies a layer of weak surface hoar and crusts (on solar aspects). Large variability in snow depths still exists in the region, ranging from almost no snow to nearly 200 cm in some areas. For average snowpack areas, expect to find weak and sugary faceted snow around 50 to 100 cm deep, which extend to the ground. This weak bottom half of the snowpack has been the culprit for large avalanches in the region over the past few weeks.

Problems

Deep Persistent Slabs

Deeply buried weak layers are an increasing concern with substantial warming and sun in the forecast. These deep layers are more easily triggered in areas where the snowpack is shallow, such as near ridges and rocky terrain.

Avoid steep, rocky terrain and shallow snowpack areas where triggering is more likely.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Wind Slabs

Wind continues to redistribute loose snow into wind slabs at higher elevations. Expect to find the deepest and most reactive pockets in immediate lee areas near ridgecrests and around wind-exposed terrain features..

Be cautious on convex rolls around treeline where buried surface hoar may be preserved.Be careful with wind loaded pockets, especially near ridge crests and roll-overs.If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 1.5

Valid until: Jan 24th, 2019 2:00PM