Fri, November 30, 2012 Turnagain Pass Avalanche Forecast

Fri, November 30th, 2012

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


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 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 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.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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