Tue, December 23, 2014 Turnagain Pass Avalanche Forecast

Tue, December 23rd, 2014

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

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

Our current problem can be described as low probability/ high consequence. The likelihood of waking up this documented layer of buried surface hoar that we’ve been talking about the last few days is waning as time ticks by and temperatures drop. However if one were to find the right trigger point (shallow areas in the slab or slope convexities are the likely areas) on a slope the resulting avalanche could be quite large. We have a hard time classifying this type of problem using the North American Avalanche Danger Scale because it doesn’t totally capture this low likelihood/ high consequence scenario with any one color.

Colors aside, it’ll be important today to travel through the backcountry with heightened awareness. Ensure good spacing between parties and individuals when ascending steep terrain; one person at a time on the slope; plan out and communicate escape routes and safety zones; ensure safe zones are safe. Keep in mind that with this avalanche problem, potential exists for a slope to avalanche wall-to-wall or even connect slopes through shallow bands of rock.

As mentioned in the bottom line, this is a “scary” MODERATE avalanche problem and though our snowpack is gaining strength, surface hoar once buried accounts for more avalanche accidents than any other weak layer.

Weather

Tue, December 23rd, 2014

Calm weather dominated the eastern Turnagain arm zone yesterday. After a light morning drizzle deposited a very thin crust on the snow surface up to about 1,500′ the skies began to break and visibility improve. Ridgetop winds were in the single digits from the east with temperatures hovering around 32 degrees at 1,000′.

We may continue to see a few snow showers through the day as instability in our region weakens with an advancing ridge moving in from the west. This will shift winds to a northwesterly direction where we may see gusts into the mid-teens or low 20’s mph today. Temperatures at 1,000′ will linger right around the freezing mark. We may also see fog development today and into tomorrow-in low-lying areas around the highway.

Looking out toward Xmas it appears that south-central AK will be influenced by westerly flow as a dominant low-pressure system in the western Aleutians tracks east toward the mainland. Expect temperatures to slowly decline and periods of light snow thru the holiday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	29	1	.1	28
Summit Lake (1400′)	24	0	0	4
Alyeska Mid (1700′)	32	1	.1	21

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	E	6	14
Seattle Ridge (2400′)	26	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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