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Friday April 07,2017

April 7, 2017 at 04:57AM

This Bulletin Valid Until: Sunday April 9, 2017 @ 6 pm. 

DANGER RATINGS (Make sure you understand the danger level meanings)
 
Outlook Friday Saturday Sunday
Alpine HIGH HIGH CONSIDERABLE
Treeline HIGH HIGH CONSIDERABLE
Below Tree line MODERATE MODERATE MODERATE

Confidence:  Moderate-  limited alpine observations 

Main Concerns: (Avalanche problems)

Wind Slab-   Strong gusting to extreme south winds and up to 100 cm of new snow during this forecast period will form 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-   Moderate to strong snowfall amounts are expected to deliver up to 100 cm of snow throughout the forecast period and will likely form storm slabs in both the alpine and at tree line. Storm slabs will be 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 (size 2) and will be touchy to very touchy to light human triggers as storm snow fall amounts increase. 

Cornice-  New snow, wind and moderate temperatures will provide ideal conditions to continue forming and growing 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: Warm temperatures, followed by a cooling trend with near sea level freezing levels promoted the development of  a supportive melt freeze crust. Beginning Tuesday a total of up to 60 cm of new snow has buried this crust and strong past wind has transported this snow into lee areas at tree line, this new crust has been found buried down 150 cm plus. Warm temperatures and rising freezing levels rapidly settled this new snow as temperatures rose 6 degrees in as little as 3 hours following the initial storm. Subsequent snowfall on Thursday was reported to be bonding well under moderate temperatures and south wind.

Avalanche Summary: No new avalanche activity reported in the last 72 hours.

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 under moderate temperatures and reports of snowmobile travel being easy with 20 cm of penetration immediately following the mid week storm cycle. 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 200 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:   A strong pacific low will pass thru the region Friday, lingering into Saturday. Forecast models predict very strong south wind and on the western edge of the forecast region precipitation amounts in the form of snow of up to 90 cm.

Fri-  up to 30 cm new snow 10 mm of rain. Winds SE to 50 km/hr.                                            Freezing level to 1400 m.

Sat- up to 30 cm new snow 0 mm of rain. Winds SW to 50 km/hr.                                             Freezing level to 1200 m.

Sun- up to 30 cm new snow 0 mm of rain. Winds SE to 35 km/hr.                                             Freezing level to 900 m. 

 

Prepared by Jesse Percival

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