Avalanche Forecast

Issued: Feb 1st, 2018 5:44PM

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

Avalanche Canada shorton, Avalanche Canada

Snow forecasts are uncertain and the snowpack is untrustworthy. Conservative decision making is critical.

Summary

Confidence

Low - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Clashing fronts make the next few days difficult to forecast. A Pacific warm front and an Arctic cold front are converging over the Rockies, creating the potential for surprise accumulations of low density snow. Timing, location, and intensity are highly uncertain (and so are the snowfall estimates).FRIDAY: The first wave of snow starts Thursday night with 5-15 cm then another 5-10 cm possible throughout the day on Friday / moderate west wind / alpine temperatures around -5 C.SATURDAY: Continued flurries with 5-20 cm possible / strong northwest wind / alpine temperatures around -5 C.SUNDAY: Ongoing flurries / strong west wind / alpine temperatures around -3 C.

Avalanche Summary

On Thursday, a few small slabs were triggered by skiers in the southeast part of the region. The slabs occurred in the top 20 cm of new snow. A few natural wind slabs up to size 2 were also reported throughout the region over the past three days.A few large persistent slab avalanches were observed this week (up to size 3), but likely occurred during the warm stormy weather on Sunday and Monday. Many of these avalanches failed on the deeper November and December weak layers, and many were triggered by cornices falling on north and east facing slopes.

Snowpack Summary

Expect waves of fresh snow over the next few days as storm snow accumulates. The distribution will be spotty, as some areas already have 30 cm and others nothing. Stay aware of the condition of the new snow. Mostly low density powder is expected, but could become heavy if it warms up. Also watch for slab development in wind affected areas.About 20-50 cm of recent snow covers a weak layer that was buried in mid-January. It is composed of feathery surface hoar in sheltered areas and a sun crust on solar aspects. Another surface hoar layer from early-January is buried 30-60 cm deep. A widespread weak layer from mid-December is composed of facets, crusts, and surface hoar and is now buried 60-80 cm deep. Finally, a weak layer of rain crusts and sugary facets buried in late-November exists near the base of the snowpack. Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread. Snowpack depths are also variable across the region and typically thinner in northern areas than in areas to the south.

Problems

Wind Slabs

An icon showing Wind Slabs
New snow and wind will form fresh wind slabs in higher elevation lee terrain. Large fragile cornices are also likely near ridge crests.
Be cautious as you transition into wind affected terrain.Minimize exposure during periods of heavy loading from new snow and wind.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

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

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Several deeply buried weak layers have the potential to produce large destructive avalanches.  Avoid exposure to overhead avalanche terrain, including cornices which have been a common trigger.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.Minimize exposure to overhead avalanche terrain, large avalanches may reach run out zones.Be aware of thin areas that may propogate to deeper instabilites.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Feb 2nd, 2018 2:00PM

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