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Monday April 10, 2017

April 10, 2017 at 06:27AM

This Bulletin Valid Until: Wednesday  April 12, 2017 @ 6 pm. 

DANGER RATINGS (Make sure you understand the danger level meanings)
 
Outlook Monday Tuesday Wednesday
Alpine CONSIDERABLE MODERATE CONSIDERABLE
Treeline CONSIDERABLE MODERATE CONSIDERABLE
Below Tree line MODERATE LOW LOW

Confidence:  Moderate-  limited alpine observations 

Main Concerns: (Avalanche problems)

Wind Slab-  Past very strong gusting to extreme south winds and up to 60 cm of new snow during the last forecast period has formed dangerous wind slabs in both the alpine and at tree line. Wind slabs will be found on lee aspects (North west thru to North east) and located in terrain features such as at the base of steep cliffs, below any cornice features, ridge top areas and steep convex rolls. Avalanches from wind slabs could be large (size 2) and will be touchy to very touchy to light human triggers as snow fall amounts continue to increase and winds persist. 

Storm Slab-  A storm slabs in both the alpine and at tree line has formed from past precipitation of up to 60 cm in many places this storm slab can be defined as a hard slab. These storm slabs have been found on all aspects and expect to find these dangerous avalanches to be prevalent in areas that offer protection from the wind. Avalanches from storm slabs could be large to very large  (size 2-3) and are stubborn to light human triggers. When trigger, expect storm slabs to run fast and far and with widespread propagation.

Cornice-  New snow, wind and moderate temperatures have provided ideal conditions to form and grow cornices.These hazardous snow features can be found on primarily north west thru to north east aspects and in both the alpine and at treeline.As temperatures rise and snow fall and wind is forecast to increase cornices will be fragile, unpredictable and when failing will deliver a heavy load to slopes below and may trigger a much larger avalanche (size 3). Give these hazardous features a wide berth when deciding to travel either above or below them.

Travel/Terrain Advice:  Dangerous avalanche conditions exist and travel in avalanche terrain is not recommended and should be avoided. If users choose to travel in to avalanche terrain plan to avoid steep open slopes and unsupported features,choose simple terrain that avoids over head hazards.

Past Weather: Snowfall and strong south east winds continue to keep mountain snow pack conditions from moving into a spring melt freeze regime. Up to 60 cm in the past week has fallen on a wide spread surface crust and strong winds pressed the upper snow pack turning in specific areas this snow into a hard slab. Mid day temperatures did rise on Saturday and the upper snow pack became moist all aspects and elevations 2000 meters and below.   

Avalanche Summary: Avalanche control teams using explosives produced numerous large (size 2- 2.5) avalanches on north and west aspects. These avalanches had crowns between 40 to 80 cm in depth and where primarily hard storm slab. Initially these avalanches where stubborn to triggering but in specific areas below ridge tops became touchy. Once these avalanches where triggered, they propagated far and wide and the avalanches ran to the bottom of there paths, with some running past historic run outs.

Snowpack Description  New snow of up to 60 cm has buried an upper surface crust that is up to 10 cm thick and was supportive to foot penetration.This new snow has settled rapidly and displays slab properties, it is however bonding well to this crust but when trigger has a high probability of propagating far and wide.Below this new snow and new crust a variety of both sun crust and wind crust have been observed and are dependent on orientation to both the sun and wind. 

 Three significant crusts exist in the upper mid snow pack with the mid February down approximately 250 cm and this being the most pronounced and supportive with facets still being found above and below this crust. The mid February crust has produced hard resistant planar results when a deep tap test was performed and continues to persist and remain a layer of concern.  As temperatures have remained moderate and upper snow pack height and weight increase, recent test profiles have shown the other crusts beginning to decrease in density and a lack of planar results between the crusts and interfaces above and below them.The lower mid and lower snow pack continue to settle and with this settlement an increase in density and strength had been noted.

Surface- New snow has buried a well developed surface crust.

Upper-  Numerous melt freeze crusts exist in the upper snow pack.

Mid-  Well settled with lingering persistent weakness found between 100 and 200 cm 

Lower- Well settled.

Weather Forecast:  Spring weather is in effect, incoming storms are less organized. Forecast models have begun to predict a decrease both in the intensity of winds and precipitation amounts, while temps and freezing levels are on the rise.

Mon- up to 30 cm new snow.  Winds SE to 50 km/hr.    Freezing level to 1000 m.

Tue- up to 5 cm new snow .    Winds NE to 25 km/hr.   Freezing level to 1400 m.

Wed- up to 25 cm new snow   Winds SE to 25 km/hr.   Freezing level to 1100 m. 

 

Prepared by Jesse Percival

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