Issued: Sat, Dec 23, 2017 at 8AM

Expires: Sun, Dec 24, 2017

Good lessons to be learned from the Pastoral Avalanche in Turnaigan. We recommend you check it out. http://www.cnfaic.org/advisories/current.php

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Above 3,500ft Moderate

2,500 to 3,500ft Moderate

Below 2,500ft Moderate

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

BOTTOM LINE

A moderate avalanche hazard exists on all aspects and at all elevations today. Natural avalanches are unlikely, human triggered avalanches are possible. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Small avalanches in specific areas; or large avalanches in isolated areas.

 


PERSISTENT SLAB AVALANCHE PROBLEM

13″ of new, low density snow from December 20th has bonded well to the old snow surfaces. E and ESE winds were moderate this week, however, strong gusts were able to transport new, low density snow and reshape the landscape in specific areas, resulting in pillows and sculpted snow features.  Pillows are 1-3 feet deep and generally bonded well to the old snow surface. They are easily identifiable in their appearance and shape (see pictures below). Aspects with loading are generally on leeward aspects, West to Northwest, but the loading pattern this week is a little more complex.

Buried in the mid-pack are lingering, old, buried, persistent weak layers (PWL’s) and old melt-freeze crusts.  The sensitivity of triggering a slab on PWL’s is stubborn to unreactive, so it still remains possible. Due to the low continuity and spatially variable avalanche problem, it will be difficult to predict where triggering an avalanche will occur.

At lower elevations the snowpack is generally thinner, which makes the buried PWL’s weaker, and potentially more reactive, but avalanche size will be on the smaller size (D1). Expect to produce audible whumphing in specific areas, especially in meadows where alders and bushes are prevalent. Shooting cracks may be possible. Triggering an avalanche 1-2 feet deep is more likely on 35º and steeper slopes. Be cautious and avoid steep creek and gully sidewalls and terrain traps.

At mid to upper elevations, expect generally good stability, but do not rule out the possibility of triggering a large avalanche on buried PWLs on slopes 35º and steeper. The problem exists on all aspects, however, it will be deeper (1-3 feet) on slopes that have received the brunt of the season’s loading, generally on leeward aspects, such as West to Northeast, and on the leeward sides of mountain gaps and passes. Pole tests will reveal an upside down cake, with more cohesive snow overlying weaker, faceted snow. More pronounced hardness differences indicate a more dangerous avalanche problem. Slabs may break above you and make escape difficult to impossible.

Use good travel protocol, ride one at a time (see video at bottom of page), avoid slopes with terrain traps. All members of your party should wear avalanche transceivers, and carry shovels and probes. Consider using radios to tighten up communication when you become spread out from partners.

The snowpack depth is highly variable, 8 inches to 3 feet, due to wind scouring and loading over the last couple of weeks.

Please view the community observation platform HERE!

Loaded pillows of soft but cohesive snow. For the most part, these pillows are well bonded to the old snow surface and stubborn to unreactive to trigger. If you are able to trigger a pillow on the old snow surface, it will likely be small (D1), but capable of sweeping you off your feet and into more risky terrain, such as terrain traps, rocks, open creeks, etc.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

PST on Marmot Mt reveals propagation potential 1-3 feet deep, in specific locations, where new snow has overloaded buried PWL’s in specific locations. Variable test results, increasing strength of PWLs over time, moderate friction, poor structure, and variable potential for propagation, all point to low continuity and high spatial variability for this avalanche problem. Translation: Generally difficult to trigger an avalanche, however, isolated areas where the right set of factors are present could result in triggering a large (≤D2) avalanche; small avalanches possible in specific terrain.

Pit data here

 

Recent Avalanche Activity

 

Peak X4068 on lower ramp to East ridge, NE, 2500′ , SS-AW-R1D1-O/G , Moose triggered storm slab, likely just after Dec. 20/21 storm. Likely new snow failing on persistent facets over MF crust.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

CONDITIONS PHOTOS

Look closely…sculpted features like these cover the landscape. They are generally soft, allowing you to ride through them without being jared. December 20th low density snow was easily affected and shaped by moderate wind speeds and strong gusts.

 

 

 

 

 

 

 

 

 

 

 

 

Scoured and loaded ridgeline on x4068

Winds sculpted snow from winds crossing this slope

More sculpted snow on Skyscraper

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Recent Weather

This week’s weather at 3550′:

Temps averaged 21ºF, with a low of 14ºF and a high of 31ºF.

13″ of new snow and 1.5″ water (SWE) was recorded at IM snotel this week.

Overnight at 3550′:

Temperature averaged 28° F.

0″ new snow overnight.

This week’s weather at 4500′:

Temps averaged 18ºF, with a low of 11ºF and a high of 28ºF.

Winds averaged E/ESE 6 mph, max E/ESE 15 mph . Gusts averaged E/ESE 12, max gusts E/ESE 30 mph.

Overnight at 4500′:

Temps averaged  26ºF overnight.

Winds averaged SE 6 mph overnight, with a max gust of 15 mph.


NWS recreational forecast for Hatcher Pass here


NWS point forecast here


State Parks snow report here

State Parks Motorized Opening Statement: The snowmobile trail corridor from the Fishhook Trailhead through Hatcher Pass will open starting on 12/22 at 6 PM. Snowmobilers are required to stay on marked/groomed trail until they are on the west side of Hatcher Pass. The snowpack is
still thin with no base in the lower parts of this area. ALL OTHER AREAS REMAIN CLOSED TO SNOWMOBILES.

Additional Info & Media

Expect the avalanche hazard to remain the same throughout the weekend. NWS is forecasting high pressure and inversion with temperatures reaching 33ºF at 3000′ tonight.

Current surface analysis as of 6 am this morning

 

 

 

 

 

 

 

 

 

 

 

 

 

Blocking high pressure along the Alcan is stalling and weakening the next weather maker moving northward from the Gulf into Southcentral AK. NWS is forecasting clearer skies through the weekend but cloudier weather with the possibility of snow flurries on Christmas day.


A good video demonstrating the need to use good travel protocol and riding one at a time.

Posted in HPAC Forecasts.
Jed Workman

Forecaster: Jed Workman