Mon, March 30, 2015 Turnagain Pass Avalanche Forecast

Mon, March 30th, 2015

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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

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

Snowfall amounts over the past several days have varied across the forecast zone. The result is slabs ranging anywhere from 6-18” in the Alpine. On East, South and West aspects these slabs sit on a thin crust. Yesterday my partner and I found these slabs to be well bonded to these crusts. Traveling along areas that were being actively loaded by wind showed no signs of instability (collapsing or cracking). Despite these encouraging results, there has been enough loading (close to 1” H20 in the Girdwood Valley) to create instability today. It will be important to be on the lookout for upside down slabs in the Alpine. Most suspect will be steep slopes receiving direct sunlight.

New snow in the Alpine is generally well bonded to underlying surfaces. Caution is still advised in terrain approaching 40 degrees as new slabs need some time to adjust. photo:Wagner

Rocky Knob Sunburst

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

While we should see mostly cloudy skies today, the sun could make an occasional appearance. If and when this happens, expect wet loose avalanches to quickly occur on terrain 40 degrees and over. Volume will be low to medium. Consequences will increase in line with the terrain. Sustained steep slopes will produce more dangerous, higher volume wet loose avalanches. If the sun pops out or the snow at your feet is wet and heavy (likely in the Treeline elevations) it will be time to back off of steep terrain.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Large unsupported masses of snow are looming over many starting zones in the Alpine. Practice good habits around cornices. On the way up pick routes that minimize time spent in the line of fire. On ridges and above starting zones keep your distance from the edge until you can see the base of the cornice and where it connects to the underlying terrain.

Weather

Mon, March 30th, 2015

Southerly flow caused by a large complex Low pressure system in the Gulf has continued to dominate the weather pattern over the last several days. This has resulted in mild temps with showery precipitation and moderate winds. The Girdwood Valley picked up 6 € of dense snow (.9 € H20) and the Turnagain Pass SNOTEL picked up 2 €/.2 (snow/H20). Higher amounts fell on the North end of Turnagain Pass.

Today that Southerly flow will continue to bring light amounts of snow and rain with only 1-2 € of snow expected. Rain/snow line should climb as high as 1,500′. Winds will be in the 10-15 mph range out of the East and temperatures at 1,000′ will rise into the high 30s F.

The extended outlook is showing more of the same as we move into the work week. Circulation around the aforementioned system in the Gulf will bring multiple rounds of precip, clouds and mild temps through at least Wednesday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	2/rain	.2	60
Summit Lake (1400′)	33	0	0	10
Alyeska Mid (1700′)	33	6/rain	.9	37

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	ENE	17	39
Seattle Ridge (2400′)	27	n/a	15	31

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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