Tue, December 06, 2016 Turnagain Pass Avalanche Forecast

Tue, December 6th, 2016

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

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

Yesterday Easterly ridgetop winds were transporting snow and loading Western aspects in the afternoon and overnight. With about 6-8” of snow available for transport, fresh wind slabs, up to 1ft thick could be tender today. Expect wind slabs to be extra touchy in rocky areas where the snowpack is thin and weak. This wind stiffened snow could also be adding stress to the Nov.16 layer of buried surface hoar where a slab up to 2’ thick could be enough to bury someone. Pillow-shaped snow on steep convexities and cross-loaded gullies will have more potential for this higher consequence avalanche. Today’s winds are expected to decrease this morning, but should you see activily loading snow or shooting cracks – these are obvious clues the snow is unstable.

Old ski tracks filled in quickly yesterday afternoon on a Western aspect on Tincan. Top of the ridge in this picture is 3600′.

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

If you have been reading our advisories over the last few weeks then you are probably well aware of the Nov.16th layer of buried surface hoar. The most recent avalanche activity on this layer was reported on Saturday, Dec. 3rd on Cornbiscuit, where a group intentionally triggered a cornice on a steep Northern chute. They observed a slab 8-10” thick pull out and identified the buried surface hoar as the culprit. There are a number of complexities associated with this avalanche problem including the knowing the full extent of where this layer remains in the snowpack. Numerous small avalanches have occurred on this layer and numerous small snow storms keep covering up the evidence. Most of this activity has been on the popular Southwest slopes of Sunburst and Tincan and little is known about places less traveled. Don’t forget this layer is on all aspects and continues to show propagation potential in test pits above 2000’. The other important thing to note is the slab character is becoming denser with recent wind events, which means the slab could break above you once well onto the slope.

Be sure to use safe travel protocols if venturing into avalanche terrain today:

Expose one person at a time
Group up in safe zones
Have an escape route planned
Watch your partners and be aware of other groups around you

Check out the results of a test pit at 3300′ on a North aspect of Tincan from yesterday, Dec.5.

Weather

Tue, December 6th, 2016

Yesterdays clear skies became overcast in the afternoon and light flurries were observed between Girdwood and Turnagain Pass. Temperatures increased throughout the day, -8F in AM to 22F by evening, along the road (1000′). Easterly ridgetop winds increased in the afternoon, 15-30mph, along ridgetops. Overnight about 2 inches of snow was recorded in Turnagain Pass and trace in Girdwood.

Today expect scattered snow showers with an accumulation of 1-4′ inches. Temperatures will likely remain in the mid to low 20F’s and winds are expected to be light from the East.

Dry arctic air continues to keep most of Alaska under a cold air mass including parts of Southcentral Alaska. With the exception of several low pressure systems tracking through the Gulf of Alaska bringing scattered snow showers to the area, temperatures are expected to remain cold throughout the week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	17	2	.2	22
Summit Lake (1400′)	14	1	.2	5
Alyeska Mid (1700′)	19	trace	.02	10

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	13	ENE	11	35
Seattle Ridge (2400′)	15	ESE	16	27

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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