Fri, February 13, 2015 Turnagain Pass Avalanche Forecast

Fri, February 13th, 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

Several days ago we received a snow event that distributed an uneven amount of snow over Turnagain Pass. On the Southern end of Turnagain slab depths average 6” with pockets as thick as 10” in wind deposited areas. On the Northern side of the pass, average slab depths are 10” with pockets 15+” in places. This new snow was also accompanied by sustained East winds (20-30’s mph) causing the slab to become denser and more cohesive in areas along ridgetops. This uneven slab distribution is sitting on a widespread unstable weak layer of facets.

We are on the scarier side of the MODERATE scale for the heart of our forecast zone. There’s not quite enough new snow in most of Turnagain Pass bump the entire area to CONSIDERABLE, but it could be challenging to know exactly where this line exists. In places where slab depths are shallower like Tincan and Sunburst isolated avalanches up to 10″ thick are possible in steep terrain. In places like Eddies and along the Northern end of Seattle Ridge where thicker slabs exist it will be more likely to propagate an entire slope.

In Girdwood the problem is a little harder to evaluate with 6” of new snow covering an older windslab (4-8” thick) which also sits on top of old weak faceted snow.

Yesterday avalanche activity was observed along the Northern side of Seattle Ridge. Forecasters triggered a remote avalanche from 300′ away near the Seattle Ridge weather station. A larger natural avalanche was also observed in this area. There was also a few reports of natural activity near the Girdwood Valley and near Seward.

This avalanche occured on a Southern aspect near Main Bowl on Seattle Ridge and was not witnessed. It is likely to have been triggered naturally yesterday.

This avalanche was triggered remotely from 300′ away on Seattle Ridge near the Seattle Ridge Weather Station.

Travel Advice

Collapsing sounds will be your first red flag warning sign. If you hear “woomphing” sounds this is a sign that your weight is enough to collapse the weak layer below the slab and reinforces your decision stay off of slopes greater than 35°.

Remote triggered avalanches are a concern for today and it is extra important to be aware of other groups within the same area. If you are traveling along a ridgeline you could remotely trigger an avalanche on an adjacent slope without even realizing it. If you find yourself along a valley floor avoid the run-out zone of large steep slope. Sunburst ridge and Taylor Pass are a good example of places to avoid today.

Careful snowpack evaluation is recomended today. Click HERE for a demonstration on how to perform a hand sheer test to help you understand our current persistent slab problem.

Additional Concern

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

Warmer temps and solar radiation have caused point releases and roller balls on Southern aspects over the last two days. In summit lake yesterday a 6” slab was triggered on Southern aspect during the heat of the day when temperatures were in the mid 30’sF in this area. It is likely that these aspects are developing a crust layer, but if the sun appears today and temperatures creep into the Mid 30’s again, be aware of wet (damp) avalanches on South facing slopes.

Weather

Fri, February 13th, 2015

Yesterday temperatures reached into the mid 30’s F below 1500′ with light rain in the morning then clearing off in the afternoon. Only a trace of new snow fell above 1500′. The sun came out in the afternoon keeping temperatures warm, with the hottest part of the day around 2pm. Ridgetop temps climbed into the high 20’sF. After sunset skies remained mostly clear and temperatures dropped into the mid 20’sF. Winds were mostly from the East and averaged 5-15mph along ridgetops.

Overnight temperatures stayed in the mid to high 20’sF and a mostly East wind has been light (5-10mph.) No new precipitation was recorded.

Partly sunny skies are anticipated today with a chance of light precipitation in the evening. Temperatures are expected to be in the low to mid 30’sF at sea level and at higher elevations. Winds from the East may pick up into the 20’s along ridgetops.

Right now it looks like our next best chance for snow accumulation will be on Sunday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	1	0.1	36
Summit Lake (1400′)	28	0	0	9
Alyeska Mid (1700′)	31	0	0.1	24

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	E	7	27
Seattle Ridge (2400′)	28	Var.	9	25

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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