Tue, April 19, 2016 Turnagain Pass Avalanche Forecast

Tue, April 19th, 2016

Alpine

Above 2,500'

1 - Low

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

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

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

In the Treeline zone (1000’-2500’) the avalanche hazard remains complex due to glide avalanches that threaten access to safer snow in the Alpine. Our biggest concern remains focused on the motorized uptrack where two large glide avalanches recently on Repeat Offender including one shortly after 5:30pm yesterday. Considering how many more cracks threaten this zone, we are recommending that people not travel on the uptrack or in runout areas along Seattle Ridge.

On the non-motorized side of the road be aware of new cracks forming in popular terrain, like the West face of Cornbiscuit and Magnum. Our message remains the same: AVOID being under glide cracks and respective runout zones. To be in the wrong place at the wrong time when a glide releases could likely be deadly.

Photo on right side was taken yesterday afternoon. This new glide avalanche occurred within the last two days and more glides threaten the uptrack.

Close up of glide cracks above the uptrack on Seattle Ridge.

Avalanche Problem 2

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

Over the last few days wet loose avalanche activity has slowed down in Turnagain Pass due to a deeper freeze in the mid elevation band. However outside of our core advisory zone, in Portage Valley, natural avalanche activity has been observed in steep channeled terrain along the Byron Glacier Trail. Extra caution is warranted in this particular area and leaving the established trail is very dangerous. Today there is possibility of both rain and sun, both of which will increase the potential for natural wet loose avalanche activity in this particular zone.

In the mid elevation zone where wet snow is falling on a hard surface triggering wet loose activity will be likely on steep terrain where the surface snow is wet. If the sun makes an appearce today small natural wet loose activity will be possible on solar aspects in the alpine. Pay attention to snow depths; wet ‘sluffs’ will be proportional to the amount of snow that falls today.

Video taken on 4/17 by a public observer who witnessed an avalanche close to the Bryon Glacier trail while hiking.

Additional Concern

Wind Slabs

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.

More info at Avalanche.org

In the Alpine there is currently not a lot of snow available for transport, but 2-3” of new snow is expected today. This combined with 20-30mph winds could form small isolated wind slabs on steep features in the alpine. Blowing snow and soft-pillowed shaped formations are clues that wind slabs are forming.

Cornice fall – Where cornices are large be skeptical of their stability. Recent cornice fall has been observed, and in some area these features are gigantic. Give them lots of space and don’t hang out underneath one.

Weather

Tue, April 19th, 2016

Yesterday skies were mostly sunny and daytime temperatures reached the mid 50F’s near sea level. At Center Ridge Weather station (1880′) daytime temperatures were in the mid 40F’s and overnight temperatures hovered just above freezing. Easterly Ridgetop winds were light increasing the moderate overnight.

Today Scattered rain showers are expected throughout the day with mostly cloudy skis, but periods of sun are always possible. Rain/snow line will be around 2500′ with an addition 0.2 € of (snow water equivalent) expected today, 2-3 € of snow in the alpine. Ridgetop winds, averaging 20-30mph, will be from the East. Daytime high temperatures for 1000′ are expected to be around 45F and overnight lows in the mid 30F’s.

Similar temperatures and showery conditions are expected tomorrow, before another possible window of clear skies on Thursday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	38	1	0.1	108
Summit Lake (1400′)	37	0	0	25
Alyeska Mid (1700′)	37	trace	0.18	93

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	29	NE	11	32
Seattle Ridge (2400′)	31	SE	14	35

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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