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Avalanche Forecast

Archived

Nov 24th, 2012–Nov 25th, 2012

Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.
Alpine
Below Threshold.
Treeline
Below Threshold.
Below Treeline
Below Threshold.

Regions

South Columbia.

This bulletin is based on limited data. Local variations in conditions are likely to exist. Check out the Forecasters Blog for further details on interpreting early season bulletins.

Confidence

Poor - Due to limited field observations for the entire period

Weather Forecast

The weather is doing a shift from a fairly active pattern to a more benign pattern through the forecast period. A cooler, dryer NW flow will be entering the mountains with patches of lower level clouds and sunny periods in the alpine. Freezing levels will stay near valley bottom, rising to 1200 m in the afternoons. Ridgetop winds will generally be light from the NW, switching to a Westerly flow on Tuesday.

Avalanche Summary

A report of a widespread cycle has occurred during the recent storm. Natural avalanches up to 2.5 ran on all aspects with good propagation. Slab depths were 40-60 cm deep and mainly confined to N- NE aspects on alpine slopes. Natural activity is likely over now, but I'm still concerned that human triggers will be a factor over the next couple days.

Snowpack Summary

Recent storm snow accumulations across the region vary from 25-50 cm. Storm slabs and wind slabs have formed and add additional load to the snowpack. This has put significant stress on the persistent weak layers below. A buried surface hoar layer has been reported. Not sure how wide spread it is across the region, but the average depth is down 60 cm and found in specific, sheltered locations. Below this (down 80-110 cm) sits the early November crust. Tests have been showing easy to moderate SP (sudden planar) pops on weak facetted crystals at this crust interface, or within the crust sandwich.The snowpack depth in the alpine ranges from 130-225 cm. Treeline near 150 cm. A sharp transition exists below treeline, where the snowpack peters out around 1300 m.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.