Avalanche Forecast

Issued: Apr 7th, 2014 10:33AM

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

ghelgeson, Avalanche Canada

Purcells.

With no refreeze Monday night, it will probably be very challenging to find terrain free of significant hazard on Tuesday.

Summary

Confidence

Fair - Freezing levels are uncertain on Monday

Weather Forecast

Synopsis: The ridging is looking a bit weaker today, but the freezing level is still forecast to top out around 2300m Monday, and its expected to remain there through Tuesday afternoon. The warming will likely be most pronounced in the southern half of the region.Monday Night: Freezing Level: 2300m - 2500mTuesday: Freezing Level: 2300m - 2500m; Precipitation: Trace; Wind: Treeline: Moderate, SW | Ridgetop: Strong, SWTuesday Night: Freezing Level: 2500m lowering to 1300m; Precipitation: 4:8mm - 4:15cm;Wednesday: Freezing Level: 1200m - 1800m; Precipitation: Trace; Wind: Treeline: Light, W | Ridgetop: Moderate, WThursday: Freezing Level: 1200m rising to 2200m; Precipitation: Nil; Wind: Treeline: Light, Variable | Ridgetop: Moderate, W

Avalanche Summary

On Saturday night a natural avalanche started on a steep southeast facing alpine feature and eventually stepped down to ground resulting in a size 4 avalanche in the central portion of the region. The avalanche was estimated to be 1000m long, 600m wide, and up to 300cm in depth.

Snowpack Summary

Recent warm temperatures have resulted in good settlement and bonding of the storm snow from last week, but there are still isolated rider triggerable wind slabs on wind exposed alpine features.Three persistent weak layers exist in the highly variable snowpack of the Columbias:The mid-March sun crust/surface hoar layer down 50-80cm still has potential for human-triggering in isolated areas. The early-March crust/facet/surface hoar layer down around 80-120cm has become less susceptible to human triggering, but still has the capacity to produce large avalanches.The mid-February crust/facet/surface hoar combo is typically down 60 - 120cm. Direct triggering of this layer has become unlikely, however, cornice fall, a smaller avalanche in motion or prolonged warming may wake this layer up, which would result in very large and destructive avalanches.Weak basal facets exist in many areas, but triggering is unlikely.

Problems

Deep Persistent Slabs

No refreeze is expected below 2200m Monday night which has the potential to wake up deeply buried weak layers in the snowpack. As evidenced by Saturday night's large natural event, avalanches failing at this interface are quite large and destructive.

Be aware of the potential for very large, deep and destructive avalanches due to the presence of deeply buried persistent weak layers.>Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

4 - 8

Wet Slabs

With no overnight refreeze, the snowpack will likely be wet and sloppy below 2200m Tuesday. Loose wet avalanches, cornice fall and even wet slab avalanches will likely be a problem all day.

Watch for clues like pinwheels, sluffing and wet surface snow, that tell you the snowpack is too warm, and it's time to head home.>Extra caution needed around cornices with current conditions.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 5

Wind Slabs

Wind slabs immediately lee of ridge crest remain sensitive to human triggering. Wind slab avalanches failing in the alpine may step down and entrain unexpected mass as they interact with wet sloppy snow below 2200m.

Minimize overhead exposure; avalanches triggered by windloading may reach run out zones.>Avoid freshly wind loaded features.>

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

Elevations: Alpine.

Likelihood

Likely

Expected Size

1 - 4

Valid until: Apr 8th, 2014 2:00PM