Friday December 11, 2020

Sunday December 13, 2020
Saturday December 12, 2020
Friday December 11, 2020
Confidence: High - Improvements in available data and ongoing observations, have provided additional strength to forecaster confidence when issuing this bulletin.

Main Concerns

Storm Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

A new and hard surface crust is now present at all elevations and aspects, this will provide a surface for not only for new snow to slide but mountain travelers as well. Caution when travelling on surfaces with inclination and ensure the ability to self arrest.

Snow depths throughout the island range from 30 to 60 cm and 100 cm plus above the 1500 meter mark. Early season conditions exist. Stay alert for open creeks, tree wells, crevasses, or other exposed hazards.

A newly formed thin storm slab has buried the rain crust. The depths will vary and depending on timing and amounts of precipitation on Sunday, expect additional load to increase the sensitivity to triggering and size. Careful snowpack observations and assessments are recommend prior to travelling into open well connected terrain.

Avalanche Summary

No new avalanches reported or observed during the past forecast period.

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Avalanche Problems

Storm Slab

This avalanche problem was formed during incremental loading over the past 48hrs. Uncertainty exist with Sundays forecast in terms of timing and amounts of the incoming precipitation. This additional load will likely increase both the size and sensitivity of this storm slab

Location: Alpine and Tree line on all aspects.

Possibility: Triggering of this avalanche problem is unlikely to possible from light loads such as skiers. Natural avalanches are unlikely.

Size: If triggered expect these avalanches to be small, and on isolated terrain features large, size 2.

Snowpack Summary

A very moist and wet snow pack has now consolidated due to the past period of cooling. At all elevations and aspects a rain crust has formed, it is beginning to provide support but boots and ski still penetrate. Most areas above the 1000 to 1200 meter mark have received an additional 5-10cm of lower density snow. This snow is slowly settling and beginning to show some signs of slab properties , overall the description of “ dust on crust” is well deserved for current snow pack conditions. The mid and lower snowpack are settled and dense with no basal instabilities present.

Snowpack Details

SurfaceThickening crust that is breakable to both boots and skis
UpperConsolidating; The higher the elevation the thicker and stronger the upper crust and snowpack becomes.
MidSettled and dense.
LowerWell settled and dense , no basal instabilities observed or reported.

Past Weather

The unsettled weather over the past 48hr period , delivered to the forecast area cooling temperatures and variable precipitation based on location. The north and western regions received upwards of 10 cm with the eastern and interior, receiving 5cm. Freezing levels dipped below the 900 meter mark with ridgetop temperatures descending to below -5.

Weather Forecast

A low pressure will move out of the forecast area Friday and in its wake a short lived high pressure will provide clear sky and sunshine Saturday. Beginning Sunday, a new frontal system will enter the region, bringing to the area increased southwest wind and precipitation. Models are currently not in agreement on both timing and amounts for Sunday, hence the the variability with the storm slab problem and weather forecast.

Friday: trace to 5cm, Winds Light from the North East, Freezing levels to 900m, Temps @1500m -3.

Saturday: Nil, Winds Light from the South East, Freezing levels to 900m, Temps @1500m -3.

Sunday: 5-20 cm, Winds Moderate to Strong from the South West, Freezing levels 800m, Temps @1500m -4.

Posted on Friday December 11, 2020 by Jesse Percival

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