Mon, March 23, 2015 Turnagain Pass Avalanche Forecast

Mon, March 23rd, 2015

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

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

It has now been 5 days since the last loading event occurred. In that time we have seen a daily cycle of melting and freezing on sunlit aspects and generally mild temps. This pattern has helped 2-3’ slabs that formed last week to become less reactive. In some areas these slabs are resting on a thin layer of weak faceted snow. In areas where we have been able to find this combo, there still exists the possibility of triggering one of these slabs. This problem is variable across the landscape, as it is not something you will find on every slope. Digging in the snow can help you to understand the problem better, but could also be misleading.

How do we manage this uncertainty? By using effective terrain management techniques. Only expose one person at a time on suspect slopes, use islands of safety for spotting and re grouping, and identity escape routes.

Recent slab avalanche at 3,500′ W aspect. Debris pile visible left of center coming out of the shadow.

Slab at head of Ingram Cr

Avalanche Problem 2

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

The more likely avalanche concern today will be wet loose avalanches. These will be generally low in volume and are easy to anticipate. Volume will increase on steep sustained slopes. As the days get longer, so does the amount of terrain that the sun affects increase. Steep slopes being impacted by direct sunshine will continue to shed shallow loose snow avalanches. Several natural wet loose avalanches that triggered shallow wet slabs were observed in the Girdwood Valley yesterday. More of the same is possible today.

Pay attention to the snow surface on sunlit aspects today. As your skis or board begin sinking more than several inches it will be important to begin dialing back slope angles.

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 grew significantly with last week’s storms. Direct sun and a lack of wind will help to weaken these features. As always give cornices a wide berth. Minimize time spent underneath and make sure you can see the profile before approaching any corniced ridges.

Weather

Mon, March 23rd, 2015

Yesterday brought abundant sunshine under clear skies. Temps were mild and winds were generally calm. No new precipitation was recorded.

Today looks to be a carbon copy of yesterday, with slightly warmer temps. Temperatures will reach into the low 40s F at 1,000′ and near 32 F along ridgetops. Winds will be calm and skies will be clear.

High pressure stretching from Southeast Alaska through Southcentral and into the interior will prevent a low pressure system centered over Bristol Bay from impacting the area. This pattern looks to break down by mid week as we return to warm and wet Southerly flow.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	0	0	55
Summit Lake (1400′)	30	0	0	12
Alyeska Mid (1700′)	35	0	0	32

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	var	4	14
Seattle Ridge (2400′)	29	var	4	15

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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