Thu, November 30, 2017 Turnagain Pass Avalanche Forecast

Thu, November 30th, 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

New snow, warm temperatures and strong Easterly winds have created dangerous avalanche conditions across our region. Over the last three days 13” of snow was recorded at Turnagain Pass Snotel (1800’), 16” at Alyeska Mid-way station, and 22” at Alyeska’s top station. This new snow has fallen on a variety of surfaces, including very weak faceted snow. Yesterday numerous natural avalanches were observed in Girdwood Valley and several were seen in Turnagain Pass, including a slab on the Western face of Sunburst in an area commonly traveled. There was also a remotely triggered avalanche in the same area. Widespread cracking and whumpfing occurred frequently and stability tests failed easily between the new snow and the underlying facets. This weak snow rests either on the ground or overlying a melt-freeze crust near the ground. Today as snow settles, slabs will become more cohesive and could propagate larger than yesterday. Triggering a slab on steep terrain will be likely, especially in leeward, wind loaded areas. This snowpack set-up has the potential to be very touchy. Collapses (whumpfs) may propagate failure over large pieces of terrain and remotely triggering an avalanche is possible. Be aware of runout distances and terrain traps. Overall it is still fairly shallow and rocky, and getting caught in an avalanche could take you for a very unpleasant ride.

A natural avalanche that likely occured early yesterday morning on the West facing slope of Sunburst in an area commonly traveled.

This avalanche was remotely triggered from at least 300-400′ away, but was not witnessed. Note the person in the backgound for scale.

Snow pit profile at 2500′, West aspect of Sunburst, just below the natural avalanche in the first photo posted above.

Avalanche Problem 2

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

In wind exposed areas of the alpine the new snow/old snow interface is more variable, and wind slabs may have formed in places without weak faceted snow underneath. These wind slabs are likely isolated, 1-2’ thick on leeward features below ridge tops. Wind slabs could be soft or hard depending on exposure to winds and if triggered could release a larger persistent slab lower down on the slope. Digging hand pits and test pits will be good tools for looking at instability, but ultimately today is not the time to be pushing into steep terrain. Avoiding slopes greater than 35 degrees is recommended.

Weather

Thu, November 30th, 2017

Yesterday rain was observed below 1000′ and varying amounts of snow fell in the mountains across our region. In the last 24hrs Girdwood received another 3 € of snow (.39 € SWE) Alyeska mid-way station and Turnagain Pass 1 € (.2 € SWE) at the SNOTEL site. Strong Easterly ridge top winds (20-40mph) decreased late morning to moderate (10-20mph) in the afternoon with gusts in the 30’s. Temperates have dropped to around 30F at 1000′ overnight, and temps are averaging in the mid 20F’s in the alpine.

Today up to 2 € of snow could fall as a front moves out of our region. Easterly ridgetop winds are expected to be 5-15mph and temperatures will cool slightly in upper elevations to the low 20F’s and temps should hover around 32F at sea level.

This weekend another round of precipitation and warm temperatures is expected as a series of storms track through the Gulf of Alaska into Southcentral, Alaska. Although there is still not much confidence in how much precip and what type will impact inland areas, Coastal regions will likely see significant rain and snow. NWS: €œWhat we are starting to be able to say with some confidence is that southern Alaska is heading into a much warmer, windier (onshore winds), and potentially wetter (rain possibly even into the interior areas) for much of next week. Stay tuned for details. €

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	34	1	.2	19
Summit Lake (1400′)	27	1	.1	7
Alyeska Mid (1700′)	30	3	.39	18

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	ENE	16	42
Seattle Ridge (2400′)	26	rimed	rimed	rimed

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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