Tue, December 09, 2014 Turnagain Pass Avalanche Forecast

Tue, December 9th, 2014

Alpine

Above 2,500'

3 - Considerable

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. Dangerous avalanche conditions.	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

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

Yesterday marked the second, and most intense, period of rain on snow. Many wet loose avalanches were observed on all aspects along with two wet slab avalanches between 1500ft to 3000ft (photos below). Today precipitation is expected to decrease with potentially .3-.5″ of rain falling below 2500ft.

Wet avalanches are common during extended periods of rain and warm temperatures. They typically start on steep terrain with rollerballs initiating under cornices, trees, rocks or underfoot that subsequently entrain more and more snow as they gain momentum and move downslope. If caught in a wet avalanche it is very difficult to escape as the heavy wet snow can quickly knock you off your feet, twist a knee or break a leg. Debris has the potential to run further than expected due to a melt/freeze crust 8-18″ below the surface (mid-pack) providing a uniform sliding surface.

Photo below is a wet slab avalanche on the West face of Lipps Ridge (2800ft).

Wet loose avalanches off of Tincan’s Southwest facing CFR ridge (2500ft)

Avalanche Problem 2

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

Despite the grim facts concerning the wet snow stated above, at the high elevations it is snowing. Above 3,500′ new snow amounts during the past 48-hours are estimated between 2 and 3+ feet in the Turnagain Pass zone – up to twice that in other areas such as Portage and the Girdwood Valley. We have little information on how this new snow is adjusting, however what we do know is this is a significant load in a short period of time that warrants respect.

Storm snow instabilities will be in form of wind slab, cornices and loose snow sluffs. With ridgetop winds and precipitation decreasing overnight, these instabilities should gain strength rather quickly. This is due to the warm temperatures of the new snow along with no known preexisting weak layers in the snowpack at these upper most elevations.

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

Although we did not see any glide avalanche activity yesterday, the poor visibility and known existence of glide cracks between 1,500 and 3,500′, is enough evidence that these types of avalanches remain a concern. As with the travel advice for wet avalanches above, today is a day to avoid slopes steeper than 35 degrees and to steer clear of runout zones.

Weather

Tue, December 9th, 2014

Yesterday’s weather was warm, wet and windy. During the past 48-hours Turnagain Pass has received 2.5 inches of water with greater amounts in the Girdwood and Portage Valleys. The rain/snow line hovered ~2000 feet yesterday and possibly up to 2500 feet in areas. Ridgetop temperatures have been ~30F and winds were predominantly from the East, averaging 30-40mph with gusts in the 60’s.

Overnight, temperatures have increased slightly and the rain/snow line looks to be just above 2000 feet with precipitation diminishing. Winds have also decreased and are remaining steady in the teens to 20’s mph along ridgetops from the East. Today, Tuesday, we are expecting .3-.5″ of rain below 2000-2500′ with 2-4″ of wet snow above. Ridgetop Easterly winds should remain in the 10-20mph range with temperatures near 30F.

The low-pressure system that moved through yesterday is headed inland today bringing a slight break in precipitation. However, warm temperatures are expected to continue over the next few days with periods of light rain and freezing rain. This should continue through Thursday, followed by another low-pressure system that could bring more precipitation closer to the weekend for Southcentral Alaska.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	36	0	1.4	19
Summit Lake (1400′)	35	0	0.2	4
Alyeska Mid (1700′)	37	0	1.3	12

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	29	E	25	61
Seattle Ridge (2400′)	31	E	18	47

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/16/23	Turnagain	Observation: Tincan Common	William Finley
11/14/23	Turnagain	Observation: Sunburst/Magnum	Adrian Beebee
11/14/23	Turnagain	Observation: Seattle Ridge	Schauer/ Creighton/ Ellis Forecaster
11/13/23	Turnagain	Avalanche: Tincan Trees	Eeva Latosuo
11/12/23	Turnagain	Observation: Sunburst	Schauer/ Creighton/ Nave Forecaster
11/12/23	Turnagain	Avalanche: Goldpan – avalanche	Mike Records
11/11/23	Turnagain	Observation: Tincan Common	Andy Moderow
11/11/23	Turnagain	Observation: Taylor Pass – Sunburst	Wadsworth / Stwertka
11/10/23	Turnagain	Observation: Tincan	Andrew Schauer Forecaster
11/10/23	Turnagain	Observation: Tincan Trees	Michael Kerst

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