Tue, December 22, 2015 Turnagain Pass Avalanche Forecast

Tue, December 22nd, 2015

Alpine

Above 2,500'

2 - Moderate

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

A skier-triggered avalanche reported yesterday and a snowmachine-triggered avalanche on Sunday point toward a snowpack that still warrants caution and respect. Wind slabs 1-3’ in depth that formed early in this last storm cycle (Saturday Dec. 19^th) resting on weak snow from early December are the suspected culprits. As winds died down on Saturday afternoon with the storm, these slabs are masked below 6-18” of soft, surface snow in places. With a lot of traffic in the backcountry over the last 2 days and good visibility (to view lots of terrain), this doesn’t appear to be a widespread problem; rather it’s pockets of instabilities waiting for a trigger. With this kind of avalanche problem safe travel practices will again be a key way to manage any uncertainties as we move in to a period of high pressure. Watching your partners, having an escape route planned, grouping up in safe zones and carry and know how to use your avalanche rescue gear will be paramount for a safe holiday season in the backcountry.

We still lack information from the periphery areas such as the Girdwood Valley, Summit Lake and now Johnson Pass/ Lynx Creek (open to snowmachines today). Generally these areas have a shallower snowpack than Turnagain pass and can potentially harbor more weak snow. If you are out and about in these zones today please consider submitting a quick observation or even just a photo or two here.

Close-up look at the crown face of a snowmachine-triggered wind slab avalanche from Sunday. More details here.

Avalanche Problem 2

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

For folks pushing in to steeper terrain today, you can expect to deal with fast moving, low to medium volume loose snow avalanches (sluffing). As temps drop and the surface becomes more unconsolidated, these will grow in size. Usually manageable if anticipated, this is an avalanche problem that can knock a skier off their feet in steep, unforgiving terrain but is unlikely to bury a person.

Lots of loose snow sluffing initiated by skiers can be seen in the fading solstice light yesterday on Widow Maker.

Additional Concern

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 a fair bit from Saturday’s storm. As we enter a several day stretch of mostly clear weather and folks are traveling further into the backcountry, don’t forget to give these features a wide berth! There are at least a couple of suspected cornice failures yesterday both on the Tincan ridge and the Sunburst ridge, likely from folks simply walking too close to the edge.

Glide cracks: Really, glide cracks?? We observed a new (in the last few days) glide crack opening up looker left of Widow Maker on the back side of Seattle ridge. As with cornices, give these features a wide berth as they are akin to the really drunk guy at the holiday party: Unpredictable!

Recent glide crack observed on the backside of Seattle ridge in Main bowl.

Weather

Tue, December 22nd, 2015

Valley fog lifted early giving way to high clouds and mostly sunny skies by yesterday’s solstice sunset (3:42PM). Winds were light and variable with temps comfortably in the teens.

Along with a 2 second increase in daylight today, we can expect almost a carbon copy of yesterday’s weather. Valley fog should burn off rather quickly with light winds from the NW in the 5-15mph range. Temperatures will be in the teens at ridgetop locations and slightly cooler (single digits) in cold sink areas such as Summit Lake and Granite campground area. No new precipitation is expected today.

Looking out a few days, souchcentral AK will be under high pressure (cold and clear) at least through Christmas eve with a chance of unsettled weather moving into the region on Christmas day.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	16	0	0	53
Summit Lake (1400′)	4	0	0	18
Alyeska Mid (1700′)	18	0	0	36

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	15	variable	3*	10*
Seattle Ridge (2400′)	15	NW*	3*	15*

*Both weather stations had periods of inoperable wind data yesterday.

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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