Avalanche Forecast
Issued: Jan 8th, 2021 1:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
Jesse Percival,
VIAC
Reports of widespread natural avalanches over the past 48 hours mostly size two with one unconfirmed size three on a North aspects at 1400 meters.
Mt Washington Avalanche control teams reported explosives triggering size 2 avalanches on unopened north aspect down 30 to 110 cm in depth.
Summary
Past Weather
The previous storms have delivered a variety of precipitation amounts, the west side of the island received in excess of 150mm of precipitation, all of this falling as snow above 1100 to 1200 meters elevation. Winds where sustain at strong from the \south east and South west with gusts in the extreme range ( 110 Km/ hr )
Weather Forecast
Friday a storm track to the north west of the forecast region will deliver to the island region , moderate precipitation, winds and freezing levels to 1000 meters. Saturday looks like a cooling trend with unsettled weather. The storm track reinvigorates on Sunday with increased wind and precipitation. Friday: 10-20 cm, Winds Moderate from the North West, Freezing levels to 1000 meters.Saturday: No new snow, Winds Moderate from the North, Freezing levels near sea level.Sunday: 20-30 cm , Winds strong from the North, Freezing levels 1000 meters.
Terrain Advice
The past storm events have delivered high amounts of snow combined with strong winds take time to choose supported terrain with little to no overhead hazard. Be cognizant of snow conditions and utilize small slopes to test and investigate the recent storm snow and its reactionary properties.Practice patience as the snowpack is still adjusting and settling from the past storm loading. Careful and cautious route finding when transitioning from scoured areas into areas of wind loaded snow.Avoid traveling below and above cornice features as they are large and touchy
Snowpack Summary
Over the past week a strong storm system has delivered significant quantities of snow with extreme winds from the South East. Evidence of extreme wind transport of snow to North aspects is at all elevations.Overall settled snowpack depths have been measured from 200cm to 400cm.A variety of crusts exist in the upper snowpack. These crusts are producing sudden planar results during moderate testing. The mid snowpack has a 20cm layer of facets that can be found down 100cm plus.
Snowpack Details
- Surface: Wind affected snow scoured on exposed South aspects with deep loading on North aspects.
- Upper: 100 cm plus of storm snow is over a crust below 1500 m and over old storm snow above 1500 m.
- Mid: A 20cm layer of facets can be found down 100cm plus.
- Lower: Well settled and dense.
Confidence
Moderate - Limited Alpine Field Observations. Increased MIN reports providing a range of good recreational information, much appreciated, please keep them coming.
Problems
Persistent Slabs
A layer of facets 20cm thick can be found down nearly a meter in the snowpack. Currently isolated testing of this layer is not producing results. This persistent layer is a concern because when it is trigger consequences will be severe. The likelihood may be low but the consequences are high, continual loading of the snowpack with the coming forecast storm is likely to increase the magnitude and perhaps reach a tipping point where sensitivity to triggering increases.
**Location:** Specific to large terrain features but found on all aspects in both the Alpine and at Treeline.
**Possibility of triggering:** Unlikely to Possible to both natural and human triggers.
**Size:** If triggered expect these avalanche to be large to very large size 2 to 3
Likelihood
Expected Size
Wind Slabs
Found on predominantly North aspects, this avalanche problem is likely to persist as wind transport is forecast to continue to load a variety of surfaces that include below 1500 meters a crust and above this elevation old storm snow.
**Location:** Predominantly on north aspects and found in both the Alpine and at Tree line.
**Possibility:** Triggering of this avalanche problem is likely to very likely from light loads such as skiers. Natural avalanches are possible.
**Size:** If triggered expect these avalanches to be small, and on isolated terrain features large, size 2.
Likelihood
Expected Size
Valid until: Jan 9th, 2021 1:00AM
