Thu, November 26, 2015 Turnagain Pass Avalanche Forecast

Thu, November 26th, 2015

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

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

Storm Slabs

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

The powerful storm that moved through last night has created a textbook avalanche scenario: Heavy snowfall (12-16+”) overnight with significant wind has rapidly loaded slopes. Although the new snow has fallen on a variety of preexisting surface conditions, the ‘rapid loading’ itself is the concern. Slab avalanches up to 2-3′ think are possible on windloaded slopes. These can release on their own, naturally, or are likely to be triggered by a person.

If you are headed out into the backcountry – steering clear of ALL avalanche terrain is advised. This includes runout zones. Keep in mind treed areas, such as Tincan and Eddies have avalanche terrain intermixed with safe terrain. Expert level snowpack and terrain assessment skills are needed to negotiate these areas safely.

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

A number of glide cracks still exist at mid-elevations on Turnagain pass, notably in areas like the Tincan trees. Travel under glide cracks should be avoided. Glide avalanches are very unpredictable and the recent warming temperatures could add to the potential for a glide to release.

Weather

Thu, November 26th, 2015

A warm Southwesterly flow has dominated the weather for the past several days. Light to moderate rain began yesterday and reached up to 2,000′ in places before turning to snow overnight. The rain/snow line is currently hovering near 500′ where it is expected to remain for the day. See snowfall and water totals below. Winds have been strong out of East averaging 30-40mph.

For today, light snowfall is expected to add 2-4″ at the mid-elevations before tapering off and allowing skies to breakup. Tonight another system moves in from the Southwest, yet is a bit cooler that the last one. We are looking at rain/snow lines near 500-1000′ with snowfall amounts in the 6-12″ range by Friday evening. More on that tomorrow!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	10+	1.1	28
Summit Lake (1400′)	34	1	0.6	11
Alyeska Mid (1700′)	33	16	2.2	25

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	ENE	30	77
Seattle Ridge (2400′)	26	SE	20	53

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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