Tue, February 02, 2021 Turnagain Pass Avalanche Forecast

Tue, February 2nd, 2021

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.

Recent Avalanches

Summit Lake: Skiers reported a natural avalanche failing near the surface on a wind-loaded slope in the Colorado/Fresno area.

Avalanche Problem 1

Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Last week’s snowfall buried a layer of surface hoar and near-surface facets that has been producing avalanches on wind-loaded slopes for the past few days. We are expecting the winds to calm down today, but unfortunately the avalanche danger will not do the same. The nature of these persistent weak layers is that they are capable of producing avalanches long after any kind of loading event. For today, the best way to stay out of trouble will be by identifying and avoiding any steep slopes with stiff snow at the surface. After several days of cold and clear weather, most slopes have 6-8” loose, unconsolidated snow at the surface unless they have seen any wind-loading since Friday. These slopes with loose snow at the surface are not capable of producing persistent slab avalanches because they are lacking a cohesive slab capable of propagating a fracture. The danger will lie on the slopes that have seen wind loading since Friday, which has built a dangerous structure with a relatively stiff slab of snow at the surface sitting on top of a layer of relatively weak snow buried 1-2′ deep.

Because we are dealing with a persistent weak layer, slopes that have seen wind loading will not gain strength as quickly as they normally would. In addition to monitoring surface conditions, be on the lookout for other key indicators of instability- shooting cracks, collapsing, and fresh avalanche activity.

Loose Snow Avalanches (Sluffs): Several days of cold and clear weather has kept the surface snow dry and loose in areas that have been sheltered from the wind. Be aware of fast-moving and high-volume sluffs in steep terrain, especially if you are traveling near terrain traps like cliffs, rocks, trees, or gullies.

Cornices: Large cornices are starting to peel away from ridgelines, opening up large cracks and becoming especially sensitive to human triggers. If you are traveling along ridgelines be sure to give them plenty of space, and minimize the amount of time you spend traveling below them.

Stiff, wind-textured surface in the Crow Creek area yesterday. 02.01.2021

This surface hoar was the culprit in a skier-triggered avalanche on Eddie’s late last week, and will continue to be cause for concern today. Photo: Nick D’Alessio. 01.29.2021

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Glide cracks continue to open up throughout the area. These avalanches are unpredictable and large– they involve the entire season’s snowpack. Avoid spending any time on or below slopes with glide cracks, as they can release unexpectedly. If you see any new glide activity, please let us know here.

Weather

Tue, February 2nd, 2021

Yesterday: We saw another day of clear skies and cold temperatures, with highs in the single digits to low teens F. Low temperatures were near or slightly below 0 in Girdwood and Turnagain Pass, and down to -14 F in the Summit Lake area. Light winds were blowing 5-15 mph at the ridgetops from variable directions.

Today: Cloud cover is expected to increase through the day today as the upper-level ridge moves out of our area. Temperatures will reach the mid- to upper teens F today, and drop down to the single digits to low teens tonight. Winds are expected to remain calm to light, blowing 0-10 mph out of the east at ridgetops.

Tomorrow: Skies will clear through the day tomorrow, with highs expected in the mid- to upper teens F. Winds are expected to remain light, at 0-5 mph out of the east at ridgetops. We could see a trace of snow overnight.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	2	123
Summit Lake (1400′)	-6	42
Alyeska Mid (1700′)	2	109

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	4	W-NE	8	27
Seattle Ridge (2400′)	2	VAR	5	16

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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