Sun, December 10, 2017 Turnagain Pass Avalanche Forecast

Sun, December 10th, 2017

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

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

As has been the theme for December, another warm storm is on the doorstep. This one will be arriving today. Winds have already picked up from the East and after a pulse of heavy precipitation for a few hours overnight, light precipitation is expected today before ramping back up tonight. I hate to say it, but the warmest temperatures we have seen so far have occurred during the past 24 hours. This has bumped the rain/snow line up to 2,600′ and possibly created some wet avalanche activity – more on that below.

Avalanche conditions: Dangerous. The weak faceted snow that sits underneath the past 2 weeks of storm snow continues to prove itself reactive. Although this layer is slowly becoming more and more buried (20″-4+’ below the surface) and showing signs of being slightly more stubborn to trigger – it remains our primary concern. Future avalanches triggered, either by the upcoming storm(s) or a person, are becoming larger and could allow a person/people on to them before releasing. Keep in mind slopes that have already avalanched could reload and release again.

This storm’s new snow and wind at the high elevations will be creating another set of avalanches problems including wind slabs, storm slabs and cornice falls. All these storm snow issues will likely be hard to see in the clouds today, however, even small avalanches due to the storm have the potential to trigger a larger slab breaking in the weak facets near the ground.

If you are headed out to the mountains today, we recommend staying off slopes steeper than 30 degrees with nothing steeper above you, be careful to avoid runout zones and bring your rain coat.

If you look closely, you can see a streak of debris down Todd’s Run on the North side of Tincan. This avalanche occurred sometime on Thursday, Dec 7th.

Natural slab avalanche occured sometime between Friday night and Saturday (Dec 8-9) in steep terrain on Seattle Ridge – photo Joe Kurtak.

Pictured below is Seattle Ridge and the common motorized up-track as seen from Tincan. This slope, along with many other in the Turnagain area, has not avalanched and suspect to do so. Remeber, weak layers are guilty until proven innocent.

–

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

Rain falling up to, and possibly higher, than 2,600′ will be falling on snow. This is a text book case for creating wet avalanches in the elevation band of 1,000′ – 2,600′ and possibly higher. Little to no snow sits below 1,000′ and therefore the hazard there is due to avalanches releasing above sending debris into this zone. Not only wet loose slides are expected, but wet slab avalanches could occur today and through tomorrow with these very warm temperatures.

Weather

Sun, December 10th, 2017

Yesterday, overcast skies and light precipitation were over the region. A pulse of heavy rain (~ 0.5″) occurred below 2,500′ overnight with an estimated 5-7″ at the higher elevations. A 24-hour total of precipitation was 1″ of rain in the Girdwood Valley and slightly less at Turnagain Pass with roughly 6 – 12″ of snow in the Alpine above 2,500′. Temperatures as you can expect with this high rain line, were warm – climbing up to 33F at 3,800′...! Winds were light yesterday and have increased overnight with averages in the 20-30’s mph with gusts up to the 60’s from a generally Easterly direction.

Today, another shot of rain, snow and wind is arriving. Winds have climbed as mentioned overnight and are expected to remain strong today through tomorrow. Ridgetops should see averages in the 20-30’s mph from the East with gusts up to 70mph or more. Precip amounts will be moderate through the day and significant tonight with a rain/snow line around 2,600-2,800′. Around .5″ rain expected today (5-7″ snow in Alpine) and 1″ tonight (10-12″ snow in Alpine).

*There is ‘High Wind Watch’ issued by the NWS tonight through tomorrow morning for Portage Valley and Turnagain Arm.

The longer term forecast continues with an active pattern, yet cooler temperatures should arrive Monday for a brief period, before a more significant cooiling trend is expected Wednesday through Friday. This means a lowering of the rain/snow line, cross you fingers!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	37	0 (rain)	0.7	23
Summit Lake (1400′)	36	0 (rain)	0.2	10
Alyeska Mid (1700′)	36	0 (rain)	1.07	18

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	30	ENE	21	64
Seattle Ridge (2400′)	33	SE	19	59

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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