Avalanche Forecast

Issued: Mar 17th, 2015 9:16AM

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

rbuhler, Avalanche Canada

South Rockies.

Lingering storm instabilities remain a concern, especially in the alpine. Avoid steep, wind loaded features and large, unsupported slopes. Use extra caution on sun-exposed slopes during the heat of the afternoon.

Summary

Confidence

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

Weather Forecast

Light precipitation can be expected Tuesday overnight into Wednesday morning. There is currently some model uncertainty regarding amounts but the region could see 2-10mm with freezing levels around 1500m. By Wednesday afternoon the clouds should break and sunny periods are possible. Freezing levels should reach around 2000m Wednesday afternoon and alpine winds should be moderate from the NW. On Thursday, a warm storm system reaches the south coast. There is currently quite a bit of uncertainty regarding the timing and track of the system into the interior regions. For the South Rockies region, it is currently looking like unsettled conditions for Thursday with mainly cloudy conditions. Freezing levels should again reach around 2000m and alpine winds may be strong from the SW to W. On Friday, light precipitation is possible but amounts are uncertain. Freezing levels may climb to over 2500m.

Avalanche Summary

We haven't received any reports recently but this likely speaks to a lack of observers. In the Lizard region, a natural avalanche cycle up to size 2.5 was reported with slabs up to 80cm thick. Similar activity is expected to have occurred in the South Rockies Region. On Wednesday, human-triggering of storm slabs remains a major concern, especially in the alpine. Wind-loaded features and steep, unsupported slopes are the most likely areas to trigger an avalanche. Loose wet avalanches are possible during the heat of the afternoon, especially on sun-exposed slopes.

Snowpack Summary

Heavy rain (up to 60 mm) on Saturday soaked the snowpack. On Sunday the rain changed to snow as the freezing levels slowly dropped. Heavy snowfall (up to 50cm) combined with strong southwest winds developed new storm slabs on all aspects in the alpine and at treeline. The thick mid-February crust was 10-30cm below the surface before the recent storm and extends up to around 2200m elevation. Below this elevation the crust is effectively capping the snowpack, preventing riders from stressing deeper persistent weak layers. In high alpine areas where the crust is not present or is less thick, dormant persistent weak layers may still be lingering and could wake-up with heavy loading or strong warming.

Problems

Storm Slabs

20-30cm storm slabs sit over a new rain crust. At lower elevations or on sunny slopes these slabs may be moist or wet. At higher elevations, the slabs are most reactive in wind loaded areas or on steep, unsupported terrain features.

Be alert to conditions that change with elevation.>Be cautious as you transition into wind affected terrain.>The new snow will require several days to settle and stabilize.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 4

Loose Wet

Solar radiation and daytime warming will likely deteriorate the upper snowpack, initiating loose wet avalanches. Overhead hazards like cornices could also fail and trigger slab avalanches from the slopes below.

Be alert to conditions that change with aspect, elevation and time of day.>Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 3

Deep Persistent Slabs

A crust/facet layer down 90-150cm still has the potential to produce very large avalanches with a heavy trigger like a cornice failure or a smaller avalanche in motion stepping down.

Be aware of thin areas that may propogate to deeper instabilites.>Caution around convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 6

Valid until: Mar 18th, 2015 2:00PM