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Avalanche Forecast

Archived

Dec 26th, 2011–Dec 27th, 2011

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

South Columbia.

The forecaster blog has great information on the current conditions and some ideas on how to manage terrain

Confidence

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

Weather Forecast

Over the forecast period a series of fronts will pass through the interior. They'll bring strong south westerly winds, accompanied by rising freezing levels and new snow. Meteorologists find it tricky to pinpoint the timing of each storm when they are embedded in a strong zonal flow. They are confident in the pattern every (18-24hrs) per system but less confident in timing, and intensity. Check out the new Forecasters Blog for more info.Tuesday: Moderate snow amounts 5-15cm in the southern part of the region, with slightly less in the north. Strong SW winds 50-80km/hr. Max temperature at 1500m -2. Wednesday: Snow amounts 15-25cms. Strong SW winds up to 60km/hr. freezing levels could rise to 1600m and steady into Thursday. Thursday: Snow amounts 15-25cms. Freezing levels should fall 1000m or less.

Avalanche Summary

Reports of rider triggered avalanches up to size 1 are continued. While previous avalanches were confined to the northern part of the region, these new reports are from further south. The focus is on elevations between 1500-2100m. While small, these new avalanches suggest that the tipping point for activity on the early December surface hoar is slowly arriving, and the problem is likely to get worse as more snow falls.

Snowpack Summary

As much as 25cm of new snow has fallen over the holiday weekend forming hard slabs and soft slabs in exposed open areas at treeline and above. The new snow also overlies soft slabs on North through East aspects and some spotty, small surface hoar/surface facets in sheltered locations at treeline and below. The new snow seems to be bonding to the upper snowpack in the North West parts of the region. Further South easy shears are being observed in the upper 20cms. This brings the total load over the mid December surface hoar to 35cm in the South and 65cm in the North. This surface hoar layer is still producing sudden planar results in stability tests and a whole block rutchblock 4 was also observed. This is certainly the layer to watch; especially if it reaches its threshold by additional snow loading or rider triggers. Check out the forecaster blog for more info/ideas on this current problem. The midpack is well consolidated and strong.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.