Sun, December 24, 2017 Turnagain Pass Avalanche Forecast

Sun, December 24th, 2017

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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

WIND was the word yesterday. Moderate to strong easterly winds are wrecking havoc in the upper elevations thru Turnagain Pass. Even mid- slope yesterday, easterly winds were actively transporting any loose surface snow available and building hard wind slabs in leeward terrain, leaving only scoured ridges and anti-tracks in its wake. Any wind slabs today will be hard and supportable (to a skiers weight) and may lure a skier well onto a slope before it fails. Be suspect of unsupported slopes steeper than 30 degrees that have a fat, smooth, pillow-type shape to them. Listen for that hollow, drum-like sound below your skis or use a pole to probe for that hard snow over weak set up. Triggering even a small wind slab could have very high consequences especially in the upper elevations where there is also a potential for initiating a much larger and more dangerous deep slab avalanche. More on deep slabs below.

Impressive wind transport in the alpine looking South across Turnagain Arm from the Forest Service office in Girdwood.

Anti-tracks and a variable surface of mostly hard, wind-affected snow left in Common bowl, Tincan.

Avalanche Problem 2

Deep Persistent Slabs

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

More info at Avalanche.org

The recipe for deep slab avalanches has been found in the upper elevations of our forecast zone, above 3000’ on slopes that did not avalanche during the early December storm cycle. The snowpack ranges from 3-5+’ thick and is sitting on weak basal facets. Observations over the last few weeks indicate this poor structure is widespread across our region in the alpine elevations. This is a high consequence avalanche problem that is impossible to outsmart.

When dealing with a deep slab avalanche problem, keep in mind:

Thinner areas of the snowpack (1-2’ thick) are likely trigger spots as well as scoured areas near rocks
Due to strong winds over the last month the snow depths are highly variable and there may be more trigger spots than we realize
Thicker areas (3-5+’ thick) will be difficult to trigger and several tracks may be on a slope before someone finds a trigger point
It is possible to trigger this avalanche from below and it could run further than expected
Large snow covered slopes that do not have piles of old debris under them are all suspect

On Wednesday December 20th, two skiers approaching Pastoral Peak remotely triggered this very large avalanche from below. Luckily they were able to run from its path and avoid being caught. This is a very scary set-up that is likely not going away soon. More info on this avalanche here.

Weather

Sun, December 24th, 2017

Clear skies and strong Easterly winds dominated our region yesterday. Generally ridge top winds were in the 20-30mph range and gusting into the 40s during the daylight hours. Winds peaked late last night with Sunburst seeing a gust to 93mph at midnight. Pockets of warm air in the Valleys were stubborn to erode with temps in Girdwood and Portage in the 40’s F thru much of the day. Ridge top temps were in the mid to high 20’s F.

Today we can expect to see 1- 3 € of snow as a weak front moves north across the Kenai Peninsula. Temperatures are expected to drop with the approach of the front and should promote snow in most areas. Ridge top winds will be in the 10-30mph range from the East. Daytime temperatures at 1,000′ are expected to be in the low 30’s F and dipping into the 20’s overnight.

Whatever precip we can squeeze out between now and the end of Christmas Day may be it for a few days as another high pressure looks to be setting up as we head back in to the work week.

**Center Ridge SNOTEL is reporting erroneous temperature data. See Turnagain Pass DOT weather station for accurate temperature at 1000′

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	**27	0	0	31
Summit Lake (1400′)	29	0	0	11
Alyeska Mid (1700′)	32	0	0	26

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	ENE	42	93
Seattle Ridge (2400′)	28	ESE	26	70

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster

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