Fri, December 01, 2017 Turnagain Pass Avalanche Forecast

Fri, December 1st, 2017

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

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

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 snowpack in the advisory area remains touchy and the hazard continues to be elevated due to the slab, 10-20″ thick, sitting on a weak layer of faceted snow. This weak snow rests either on the ground or overlying a melt-freeze crust near the ground. This is not a set-up that will stabilize quickly, i.e. persistent slab. As the slab becomes more cohesive it may actually become more consequential. Yesterday the snowpack was “talkative” and observers noted many whumpfs, shooting cracks and some remotely triggered avalanches. These are all red flags. The snowpack is clearly saying, “Hey, I am unstable!” Step off of the skin track once in while and if you hear or feeling something let your group know. Triggering a slab on steep terrain remains likely, especially in leeward, wind loaded areas. Collapses (whumpfs) may propagate failure over large pieces of terrain and remotely triggering an avalanche is possible. This means you could trigger an avalanche from below while putting in a skin track. Eddies and Seattle Ridge both have this potential. Many slopes have slid but that doesn’t mean that the ones that haven’t, won’t. Steep slopes with cracking on them may still release. Be aware of runout distances and terrain traps. Overall it is still fairly shallow and rocky, and getting caught in an avalanche could take you for a very unpleasant ride. Staying on slopes less than 35 degrees will be crucial in terrain choices today. In addition pay attention to other groups in the area. Where you step may cause an avalanche in steeper terrain onto another party or you may expose yourself to another groups remote trigger.

Small avalanche remotely triggered yesterday by stepping off of the skin track.

Avalanche triggered remotely by snowboarder on the adjacent slope. Photo: Mike Ausman

Avalanches in a gully feature, Tincan Trees.

Avalanche Problem 2

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

In wind exposed areas of the alpine the new snow/old snow interface is more variable, and wind slabs may have formed in places without weak faceted snow underneath. These wind slabs are likely isolated, 1-2’ thick on leeward features below ridge tops. Wind slabs could be soft or hard depending on exposure to winds and if triggered could release a larger persistent slab lower down on the slope. Today is not the time to be pushing into steep terrain. Avoiding slopes greater than 35 degrees is recommended.

Avalanches off of CFR and the ridge below in leeward terrain.

Weather

Fri, December 1st, 2017

Yesterday was partly cloudy with light easterly winds that shifted to the west overnight. Temperatures were in the mid 20Fs to mid 30Fs during the day and cooled into the low 20Fs overnight.

Today will be mostly sunny with highs in the upper 20Fs. Winds will be light and southerly. Overnight there is a chance of snow, 1-2″. Temperatures will drop into the low 20Fs-high teens.

Tomorrow will be mostly cloudy with snow showers. Another 1-2″ is forecasted to fall. The storm track for Saturday looks to favor the Susitna Valley as it moves up Cook Inlet from the SW. The next system on Sunday is a low with the favorable SE flow that could bring precipitation to the advisory area. The NWS forecast discussion this morning was less confident on the timing and details. Definitely stay tuned for precipitation amounts, wind speeds and temperatures… think cold thoughts.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	0	0	18
Summit Lake (1400′)	25	0	0	16
Alyeska Mid (1700′)	28	0	0	7

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	E	9	22
Seattle Ridge (2400′)	25	rimed	rimed	rimed

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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