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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, November 30th, 2012 - 7:00AM
Expires
Sat, December 1st, 2012 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

We are issuing advisories 5 days a week through November on Sat, Sun, Tue, Thur and Fri.

BOTTOM LINE
There is a MODERATE danger today above treeline for both wind slab and persistent slab avalanches. A bump in the northeast winds yesterday evening, combined with similar conditions today, will warrant keeping an eye out for areas with recent wind deposited snow. Additionally, the possibility remains to trigger a slab breaking near the ground on steep upper elevation slopes. Loose snow sluffing is also becoming common as the snowpack deteriorates. Below treeline there is a LOW avalanche danger.

Fri, November 30th, 2012
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
1 - Low
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
More info at Avalanche.org

The northeast winds picked up to the 20-30mph range at the ridge top weather stations late in the day yesterday and though they have decreased this morning, are forecast to pick back up today. Watching for areas with recent wind loading will be a good idea as there is plenty of loose faceted snow available for transport to form touchy wind slabs any place the wind blows.

Surface conditions above treeline yesterday consisted of loose near surface facets with a thin (2-5mm) wind skin on the ridgelines where the wind was just starting to blow. Good sized surface hoar (2-5cm+) on top of the faceted snow is growing at the lower elevations and creek bottoms.

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

The persistent slab problem we have been mentioning for almost the entire month of November is fading away, finally. The October facets are just as loose as they have always been but the slab on top of them is almost as weak, if not just as weak, as they are. In areas where a poor structure remains (a slab of cohesive snow over non-cohesive snow) the slab is quite stubborn and hard to trigger. The threat is diminishing but the possibility remains that someone could find one of these slabs in just the right upper elevation steep slope.

Our meager November (22” of total snowfall…) has one more day, today, but for those interested in our weather history chart click HERE.

Weather
Fri, November 30th, 2012

The downright cold temperatures we had yesterday are even colder today. This morning it is -17F in Portage and +12F at the Sunburst weather station (3812ft). The warmest place on the mountain seems to be around 2000ft where the SNOTEL is reporting a tropical +18F! That is a 35 degree warm up from sea level to treeline (impressive inversion). Winds picked up from the northeast yesterday to 10-15mph, with gusts to upper 20’s, and should remain in this range today. The strong winds seen in other areas due to the state-wide pressure gradient seem to be splitting around the Kenai Mtns for the most part.

Looking into the crystal ball, the blocking high pressure over mainland Alaska and the bering will start breaking down Monday. Models are showing a shot of precipitation hitting PWS Tuesday into Wednesday – will this verify, and if so, any snow spill over onto our side of the mountains is the question. Cross your fingers.


This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).  

Kevin will issue the next advisory Saturday morning, December 1st.

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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.