Mon, January 11, 2016 Turnagain Pass Avalanche Forecast

Mon, January 11th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

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

After two warm Pacific storms moved through over the weekend, it seems we will get a break in weather for the next few days. Precipitation and snowfall totals from Friday through this morning are listed below. The numbers are in ‘water equivalent’. The rain/snow line has been fluctuating between 1,000′ and 2,000′ during this three-day stretch.

Friday Saturday Sunday STORM TOTAL
Turnagain Pass 1.1 + 0.4 + 1.4 = 2.9″ water equivalent (~20″ dense snow)
Girdwood Valley 0.7 + 1.2 + 0.8 = 2.7″ water equivalent (~20″ dense snow)
Summit Lake 0 + 0.1 + 0.1 = 0.2″ water equivalent (~2″ dense snow)

Due to very limited visibility yesterday, we do not have information for the Alpine elevations. We can expect however, with dryer snowfall (adding 10-12″ yesterday) at these higher elevations and strong winds, natural wind slab avalanches, as well as cornice falls, were occurring. With the possibility for clearing skies today, things to watch for will be wind slab avalanches and cornices. Keep in mind:

– Easterly ridgetop winds are forecast to remain strong enough to transport snow above treeline today (20-30mph)

– Although winds are generally Easterly, they can be channeled by the terrain and load, or cross-load, a variety of aspects

– Watch for, and steer clear of, slopes being actively loaded

– Watch for smooth rounded surfaces and hollow feeling snow, stiff snow over softer snow

– Informal tests, such as sticking your boot (or pole) in the snow to feel if softer snow sits under stiffer snow, can be great ways to assess if there is a wind slab. This should be done on low angle slopes without avalanche potential before venturing onto steeper terrain.

Avalanche Problem 2

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Cornices have grown considerably during the past few weeks. Not only do they have the potential to fall naturally, but also to be triggered by the weight of a person or snowmachine. They can also trigger an avalanche below and, all in all, be VERY dangerous. Travel under or on them should be avoided. And remember, they have the tendency to break farther back from the ridge than expected.

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Glide cracks have been appearing throughout Turnagain Pass over the last couple weeks. As you travel through the backcounty this week, pay attention for large open cracks in the snow, ‘crevasse looking’ features, these can release spontaneously without any warning. Similar to managing cornices, it is best to avoid traveling on or under slopes with glide cracks.

Photo below was sent to us yesterday from Turnagain Pass. These glide cracks are in the Treeline elevation band (between 1,000′ and 2,500′). Although the cracks are slightly obscured by yesterday’s snowfall, you can still see them looming.

Weather

Mon, January 11th, 2016

Yesterday’s pulse of moisture ended up being a bit more potent than forecast, as mentioned above. Turnagain Pass saw roughly 10-12″ of snowfall above 2,500′ and rain at the road elevation. Along with the snow and rain, ridgetop winds were strong, blowing in the 30’s and 40’s mph with gusts over 70mph. Temperatures were warm, 37F at 1,000′ with a rain/snow line hovering right around 1,600′ (give or take).

Today we should see skies begin to breakup and precipitation to continue to diminish. Ridgetop winds, on the other hand, are forecast to remain moderate to strong from the East – averaging in the 20-30’s with stronger gusts. Temperatures will remain warm as well, in the mid 20’s F on the ridgetops and near 35F at 1,000′.

Tuesday through Thursday it looks like we should have a break between storms. Temperatures are forecast to cool slightly, skies clear off and winds shift to a Northerly direction. Stay tuned.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	8	1.4	91
Summit Lake (1400′)	35	1	0.1	27
Alyeska Mid (1700′)	33	1	0.75	64

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	NE	40	78
Seattle Ridge (2400′)	27	N/A	N/A	N/A

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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