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Avalanche Forecast

Archived

Jan 14th, 2013–Jan 15th, 2013

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

Regions

South Rockies.

I’ve gone with the GEM global solution that shows a big warm up, thus this forecast is based on rapidly increasing temperatures.  If it doesn’t warm up, then these danger ratings are one notch too high.  See the forecasters blog for warming details.

Confidence

Poor - Timing, track, or intensity of incoming weather is uncertain for the entire period

Weather Forecast

The models can’t decide whether or not warm air will make its way into this corner of the province.  I’ve gone with the GEM global solution that shows a big warm up, thus this forecast is based on rapidly increasing temperatures.  Tuesday: Winds out of the NW at extreme values. Freezing level rising to 2500m+ around lunch time.  No snow/rain. Clearing skies.Wednesday: Freezing level stays high around 2300m.  Strong/Extreme NW winds persist.  No precip expected.Thursday: Freezing level comes down to 2000m.  Winds switch to westerly strong.  Increasing to westerly extreme in the afternoon.

Avalanche Summary

No new significant avalanche observations, just a bit of surface sluffing.

Snowpack Summary

Thin 1F wind slab 5 - 10 cm thick formed Sunday, hasn't been very reactive.  Below this around 60cm of settled snow rests on a myriad of old surfaces (January 4th interface) that include sun crust on steep south and west facing terrain, surface hoar in sheltered locations at treeline and below and facets everywhere else. The bond at this interface has tightened up and gained a lot of strength with the cold temps. The midpack is well settled and strong with one or two (location specific) crusts deep in the snowpack. These crust/facets combos are largely dormant, with the only concern being triggering from a shallow snowpack area or with a heavy trigger.

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.