Fri, April 15, 2016 Turnagain Pass Avalanche Forecast

Fri, April 15th, 2016

Alpine

Above 2,500'

2 - Moderate

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

Yesterday’s unexpected sunny weather and warm daytime temps appear to have accelerated yesterday’s glide activity. Numerous glides released between Turnagain Pass and Girdwood Valley including 3 that were captured by the DOT webcam on Repeat Offender during the heat of the day (2:30pm to 6:30pm.) The fact that we have been experience multiple nights without freezing temperatures in the 1000’-2000’ is concerning. This current snowpack combined with today’s weather (rain and possible sun) has us prepared for another round of glide activity.

Today we will continue to push our message to avoid all slopes with existing glide cracks, including all runout zones. Due to the dangerous and destructive power of even a small glide avalanche, we are recommending that people do not travel in avalanche terrain on the motorized side of Turnagain Pass (this include the up-track). Glide avalanche hazard also exists on the non-motorized side of Turnagain Pass. If you were to be in the wrong place at the wrong time getting caught up in a glide avalanche would not be survivable.

Glide activity yesterday on Repeat Offender, Seattle Ridge, as observed by the DOT web cam.

Close up view of the Seattle Ridge up-track. Notice all of the glide cracks in this area and a natural wet loose avalanche that occured mid day yesterday (4/14)

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

Yesterday numerous natural wet loose avalanches were observed on Southeast aspects due to intense solar heating. This wet loose activity started around 3pm when temperatures spiked and continued into early evening paralleling yesterday’s glide cycle. Yesterday’s sunny weather was a good reminder of how vulnerable the snowpack is right now in this mid elevation band, where a superficial crust quickly lost its strength.

Below 2000’ overnight temps have remained just above freezing and we have already seen 0.3” of rain in Turnagain Pass and Girdwood Valley. Today we should expect rain and sun, both of which will add stress to the snowpack. If the snow is unsupportable and your skis/snowmachine start sinking into punchy wet snow, this is an obvious sign the snow is loosing its strength. Today it is important to stay off steep slopes below 2500’.

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 it will be important to be aware of terrain features that could harbor newly formed wind slabs. On leeward aspects and on shaded aspects where the snow is drier, triggering a wind slab (6-10″ thick) will be possible. Evaluate snow and terrain features carefully and be on the look out for shooting cracks or blowing snow.

Cornices remain large and warm daytime temperatures will be adding additional stress. Give them extra space and remember they have a tendency to break much further back than expected.

Weather

Fri, April 15th, 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 reached a high of 50F at 2pm and overnight temperatures hovered just above freezing. Easterly Ridgetop winds were, 10-25mph. Overnight 0.3″ of rain was recorded.

Scattered rain and snow 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. Ridgetop winds, averaging 10-20mph, 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 through the weekend.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	38	rain	.3	112
Summit Lake (1400′)	40	0	0	29
Alyeska Mid (1700′)	38	rain	.3	97

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	28	ENE	15	37
Seattle Ridge (2400′)	31	E	11	26

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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