Avalanche Forecast

Issued: Jan 23rd, 2018 4:48PM

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

jmcbride, Avalanche Canada

South Rockies.

Recent storm snow and wind are adding to a snowpack with several buried weak layers. Best to make conservative terrain choices and avoid wind-loaded areas.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

TONIGHT: Flurries. Accumulation Trace. Ridge wind strong, southwest. Temperature -5. Freezing level valley bottom.WEDNESDAY: Mainly cloudy, flurries. Accumulation 2-5 cm. Ridge wind strong, southwest. Temperature near 0. Freezing level rising to 1600 m.THURSDAY: Mix of sun and cloud, flurries. Accumulation Trace. Ridge wind moderate to strong, southwest. Temperature -4. Freezing level 1100 m. FRIDAY: Mix of sun and cloud. Ridge wind moderate, west. Temperature -5. Freezing level valley bottom.

Avalanche Summary

no new reports of avalanches since saturday whenexplosive control in the Castle area produced several Size 2-2.5 storm slabs around 40 cm deep. Ski cutting in the same area produced numerous smaller (Size 1) releases also confined to the recent storm snow.Looking forward, expect ongoing strong winds to promote lee loading as well as slab formation and reactivity even as snowfall tapers off.

Snowpack Summary

Up to 30 cm of recent storm snow now covers both a new layer of feathery surface hoar in sheltered areas as well as sun crust on solar aspects buried mid-January, and about 50 cm below the surfaces lies the early-January surface hoar layer.About 60-80 cm below the surface a weak layer of feathery surface hoar crystals and/or sun crust buried mid-December is found at treeline and below treeline elevations. Deeper in the snowpack, another weak early-season layer of rain crust and sugary facets buried late-November exists. 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

Winds will continue to build wind slabs in lee areas at treeline and above. Slabs that form in openings at lower elevations may overlie a layer of touchy surface hoar.

If triggered, wind slabs may step down to deeper layers and result in large avalanches.Use caution in lee areas in the alpine and treeline. Wind and storm snow are forming touchy slabs.

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

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Persistent Slabs

Several weak layers of concern are buried within the snowpack and have the potential to produce large avalanches. Conservative terrain with moderate-angled, supported slopes are good choices.

Watch for signs of instability such as whumpfing, or shooting cracks.Be aware of thin snowpack areas where deeper weak layers may be more sensitive to triggering.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1.5 - 3

Valid until: Jan 24th, 2018 2:00PM