Tue, January 14, 2020 Turnagain Pass Avalanche Forecast

Tue, January 14th, 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

Over the past several days, the region has experienced winds capable of transporting loose snow. As a result, wind slabs have formed in many exposed areas of the Alpine and Treeline elevations. Due to varying wind directions and localized geography, some areas have experienced this wind effect more than others. Because of this it’s especially important to pay close attention to indicators of wind slab formation where you are and where you’d like to go. These clues of wind effected snow could include: firm surface conditions, cracking, hollow or drum like sound/feel, and visual cues of recent wind activity such as pillowing and scouring. If you find these indicators, it’s prudent to reassess the plan.

Observers from Summit Lake to Crow Pass have found hard wind effected snow along ridgelines and through valleys that channel the wind. Small natural and human triggered wind slabs have been observed and the avalanche that occurred Friday evening on the Crow Pass trail was a large hard slab avalanche involving wind effected snow.

Wind transported snow observed at Mt Adair south of the advisory area. 1.13.2020 Photo: Alex McLain

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

Persistent is defined as: “continuing to exist or endure over a prolonged period.” Related and synonymous words include: dogged, insistent, patient, persevering, tenacious, assured, certain, dedicated, determined, firm, hell-bent, intent.

Whether you like it or not, persistent layers including buried surface hoar and facet layers exist within the snowpack. These weak layers have been found 1-3′ deep and have a slab formed on top of them. It remains possible for a human to trigger a large slab avalanche. With that said, the trend of this concern is moving toward unlikely. The confusing part is these weak layers cannot be found everywhere throughout the advisory area. The only way to know if they exist where you’re located is to dig and test. If this type of investigation is not within your skill-set, it’s probably sound to assume they exist. As always, good travel practices are called for: minimizing exposure and traveling one at a time, or choosing routes with lower angles, and outside of the run out of an avalanche path.

In this non-windloaded test pit at Tincan, observers found good stability and no concerning weak layers. 1.13.2020. Photo: CNFAIC Archive

Additional Concern

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

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 on longer sustained slopes. Expect sluffing in steep terrain with loose snow. Remain mindful when traveling over cliffs and rocky outcrops.

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

Glide avalanches: Glide cracks continue to open but there have been no recent reports of glide avalanches. Due to their unpredictable potential to release, the travel advice remains the same: limit your exposure while traveling under glide cracks.

Weather

Tue, January 14th, 2020

Yesterday: Cloudy skies with valley fog. Temperatures were in the teens and dropped into the single digits in the evening. Winds were northwesterly 5-15 mph gusting into the 20s.

Today: Sunny trending to partly cloudy in the evening. Today’s high temperature is expected at 6°F, with a low of -1°F. Winds are forecast to be from the northwest from 15 to 20 mph.

Tomorrow: Clear skies with a high temperature near 2°F, low of -2°F. Winds are expected to be from the northwest to north from 5 to 10 mph.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	10	1	0.1	40
Summit Lake (1400′)	8	0	0	13
Alyeska Mid (1700′)	11	1	0.01	35

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	10	W	8	18
Seattle Ridge (2400′)	8	NNE	3	7

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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