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Avalanche Forecast

Archived

Jan 13th, 2014–Jan 14th, 2014

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

Regions

South Rockies.

Confidence

Fair - Freezing levels are uncertain

Weather Forecast

Overnight and Tuesday: Windy, warm, and wet overnight. Very strong to extreme West-Northwest winds and freezing levels rising up to about 1500 metres, with 5-10 cm of snow above 1300 metres overnight. Winds should lower to about 60 km/hr from the Northwest by mid-day as precipitation ends.Wednesday: No precipitation is expected. Winds are forecast to increase to very strong Westerly and freezing levels may climb up to about 1800 metres.Thursday: Mostly clear with above freezing temperatures in the alpine.

Avalanche Summary

No new avalanches reported. Suspect extreme Westerly winds and warm temperatures have developed hard wind slabs. Areas with snow available for transport may have continued to experience natural wind slab avalanches. Forecast warm temperatures, limited precipitation, and continued very strong winds are expected to develop hard wind slabs and decrease natural avalanche activity. Avalanches that are triggered are expected to be large due to the amount of recent storm snow. Large storm snow avalanches may step down to buried persistent weak layers resulting in very large destructive avalanches.

Snowpack Summary

Intense snow transport was reported from the Flathead area on the weekend. Expect extensive wind transport and wind slab development in all areas of the region. Recent storm snow varies from 40-70 cm across the region and I suspect that in some alpine areas storm snow has been transported into slabs that are more than a metre thick. Persistent weak layers of buried crusts/facets/surface hoar continue to be a concern, and may have been the failure plane for recent large natural avalanches. Very warm and windy conditions are expected to continue for the next few days. In the long term the warm temperatures should help with some settling and bonding of the buried weak layers. In the short term I don't like the hard wind slabs above weak layers with a rapid change in temperature.

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.