Sun, January 12, 2020 Turnagain Pass Avalanche Forecast

Sun, January 12th, 2020

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.

Avalanche Problem 1

Wind Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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

Light to moderate winds have been over the region for the past several days. They were consistently moderate last night and are forecast to continue today. Combine these wind speeds with unconsolidated surface snow throughout the region, and the potential for wind slabs to form in the lee of ridges and gullies also increases. Additionally, finding and triggering an older wind slab is possible. These slabs could be sitting on weak faceted snow, which can make them easier to trigger. Watch for blowing snow and changing surface conditions today. Look for visual signs that slopes have been loaded by the winds, these often have a rounded shape and will likely exist in the lee aspects. The snow may feel stiffer, hollow and crack around you. These are all signs of a potential wind slab.

Recent wind slab avalanche at 2700′ on east aspect of Colorado peak. Suspected skier trigger from previous 1-2 days. 1.11.2020. Photo: Anonymous

Another image of the recent wind slab avalanche at 2700′ on east aspect of Colorado peak. 1.11.2020. Photo: Anonymous

Avalanche Problem 2

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

Size of Avalanches

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

Faceted weak layers and a layer of buried surface hoar remain within the snowpack. We’ve found these layers mostly 1-3 feet deep and showing signs that they are becoming harder to trigger with time. Signs of instability are not usually present before a slope releases in this case and many tracks can be on a slope before someone finds a trigger point. Thin areas in the snowpack are the most likely places to trigger a slide, they are often near rocks and on top of rollovers. As always, good travel practices are in order: watching our partners, expose only one person at a time, remaining aware of consequences if the slope does slide, and choosing up and down tracks with forethought.

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 ooze open. We haven’t seen or received reports of glide avalanches, yet they remain an unpredictable. Travel advice remains the same: limit your exposure while traveling near and underneath glide cracks.

Oblique view of the glide cracks from Cornbiscuit, 1.10.20. Photo: Allen Dahl

Loose snow sluffs: On slopes out of the wind the surface snow is becoming looser and looser by the day with the cold temperatures. Sluffs are getting larger because of this and gaining volume in longer sustained slopes. One observer described almost having a close call with his sluff on Friday. The faceting is more pronounced at lower elevations. Expect larger sluffs in steep terrain.

Cornices: Give cornices plenty of space and limit your exposure when passing beneath them.

Weather

Sun, January 12th, 2020

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

Yesterday: Mostly clear and cold. A temperature inversion caused higher elevation temperatures to range from 5-10°F, while the valley bottoms -25 to -10°F. Ridgetop winds were from the northwest between 5-10mph with gust into the teens.

Today: As a front pushes through the region, cloudy skies will prevail with warmer temperatures and a few snow flurries. Only a trace to 3″ of snow is expected along with temperatures in the teens and a period of increased easterly winds, 10-20 mph with gusts into the 30s. A return to cold and clear weather is expected tomorrow and into next week.

Tomorrow: Mostly cloudy skies trend to become clear, with temperatures falling back to single digits. Northwest wind 10 to 15 mph.

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	7	38
Summit Lake (1400′)	-6	14
Alyeska Mid (1700′)	7	33

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	9	VAR	8	19
Seattle Ridge (2400′)	9	E	7	18

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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