Avalanche Forecast

Issued: Mar 23rd, 2015 9:38AM

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

rbuhler, Avalanche Canada

Cariboos.

Storm slabs remain sensitive to human-triggering. A deep weak layer has also been reactive and has resulted in very large avalanches. Use a conservative approach to travel and stick to mellow terrain until conditions improve.

Summary

Confidence

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

Weather Forecast

Unsettled spring conditions are expected on Tuesday. A mix of sun and cloud is forecast with localized convective snow flurries possible. Freezing levels are expected to reach around 1700m with light alpine winds. Good overnight recovery is expected with freezing levels falling to near valley bottom Tuesday overnight. On Wednesday, a warm storm on the coast spills into the interior bringing light precipitation. Models are currently showing 5-15mm between Wednesday afternoon and Thursday afternoon. On Wednesday, freezing levels are expected to reach around 1700m and alpine winds are expected to become moderate from the SW. On Thursday, freezing levels are forecast to reach 2500m by the end of the day.

Avalanche Summary

A widespread natural avalanche cycle occurred on Saturday with storm slabs up to size 3 being reported. On Sunday, natural avalanches tapered off but were still occurring on sun-exposed slopes. Many explosive and human-triggered storm slab avalanches were reported on Sunday. These avalanches were failing on a crust layer from mid-March and also stepping down to a deeper crust/facet layer from mid-February.Â At lower elevations, these slabs were moist or wet. Many remotely triggered avalanches were reported from up to 100m away. On Tuesday, human-triggered storm slabs and persistent slabs remain a serious concern, especially in steep alpine terrain. If an avalanche steps down to the persistent weak layer, very large and destructive avalanches are possible.

Snowpack Summary

At higher elevations, 40-60cm of dense storm snow sits over the mid-March interface which had included crusts, moist snow, wind affected surfaces, and/or old wind slabs. Anywhere from 80-120cm now sits over the mid-February persistent weak interface. This interface has recently been very reactive and has produced very large avalanches. In exposed terrain, strong SW winds had redistributed the new snow into wind slabs on leeward features. On Sunday, the snow surface was reported to be moist below around 1800m. The snow surface is now expected to be undergoing melt-freeze cycles as freezing levels drop overnight.

Problems

Storm Slabs

Storm slabs up to 60cm thick may overlie a weak layer and remain reactive to human-triggering. These slabs may be moist or wet at lower elevations.

Use conservative route selection, stick to moderate angled terrain with low consequence.>Avoid steep, open slopes.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Persistent Slabs

The persistent weak layer buried mid-February is down up to 1m below the surface and has produced many large avalanches recently. Storm slab avalanches could easily step down to this layer.

Be aware of the potential for wide propagations and remote triggering.>Avoid convexities or areas with a thin or variable snowpack.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

3 - 6

Valid until: Mar 24th, 2015 2:00PM