Tue, March 03, 2020 Turnagain Pass Avalanche Forecast

Tue, March 3rd, 2020

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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

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

Steady winds capable of transporting snow yesterday continue to impact the region today as temperatures drop into the single digits °F.

With no new snow expected, wind transported snow is the driving factor forming wind slabs on leeward features. If you can see wind being transported, wind loading is occurring on leeward features, and could be forming slabs. These could be hard slabs, or soft slabs. Look for cracking and collapsing and/or pillowed features. Even a small wind slab in steep terrain could sweep a rider down slope. Remain mindful while traveling above rocky features or cliff terrain.

Additionally, a layer of surface hoar formed at the end of February has been preserved in some areas not impacted by sun and wind. This layer has been observed 4″-10″ (10-25cm) below the surface in non wind effected areas. Where this layer is wind loaded, slopes could be easier to human trigger.

Active wind transport in the Seward area above the Snow River drainage. Wind transported snow was observed throughout the region. 3.2.2020 . Photo: CNFAIC archive

Buried surface hoar formed at the end of February was found 10-25cm below the surface in the Crow Creek drainage. 3.2.2020 . Photo: CNFAIC archive

Loose snow avalanches: On steep slopes protected from wind effect, watch for either very soft storm slabs or sluffing.

Cornices: Avoid travel on cornices and limit exposure under them.

Sun effect: It’s the time of year that sun can start to be an issue. As skies clear, watch for changing surface conditions on steep solar aspects.

Avalanche Problem 2

Deep Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

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

There is still a chance of triggering a slab that fails 3-6+ feet deep on the buried weak snow that formed in January. The likelihood is decreasing but the concern remains. The consequences of hitting the wrong spot are not to be taken lightly. As always it is important to use good travel protocol. Expose one person at a time and avoid terrain traps.

Things to keep in mind:

The snowpack can feel ‘stable’ and no signs of instability may be present before a deep slab releases.
The likelihood of triggering a large slab increases if you find shallower spots in the snowpack and near rocky areas.
Areas with little traffic so far this year are also more likely for triggering a deep slab.
Slopes may already have tracks on them could still release.
These slabs can be triggered remotely, from the bottom, top or side.

Weather

Tue, March 3rd, 2020

Yesterday: Skies were mostly cloudy with light snow showers in the morning. Winds were westerly at 5-15 mph gusting into the 20s. Temperatures were mostly in the 20°Fs cooling to the single digits in the evening.

Today: Partly sunny skies will trend toward mostly cloudy this evening. Temperatures will produce a high near 11°F and low of -14°F. Winds are expected from the west at 15-20 mph with a trace of snow possible.

Tomorrow: Mostly clear skies are expected with a high near 5°F and a low around -14°F in the evening. West to northwest winds are forecast at 10-15mph. No precipitation.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	18	0	0	75
Summit Lake (1400′)	16	0	0	32
Alyeska Mid (1700′)	18	4	0.2	86

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	9	WNW	7	28
Seattle Ridge (2400′)	12	WNW	7	24

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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