Tue, December 05, 2017 Turnagain Pass Avalanche Forecast

Tue, December 5th, 2017

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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

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 advisory area continues to be in an unsettled weather pattern. Snowfall, rain and wind will continue to add stress to the snowpack. Yesterday was a lull in intensity after 2-3′ of snow (2-3″ of rain at sea level) fell and winds gusted over 100mph on Saturday. There was evidence of an avalanche cycle during the storm observed yesterday. This was not quite as widespread as expected which leaves many slopes suspect and human triggered avalanches likely and additional natural avalanches possible. An example illustrating this point is that avalanche hazard mitigation in the Girdwood Valley yesterday produced avalanches running to ground on slopes adjacent to natural avalanches that had run in the storm. Translation: slopes that haven’t slid could be hanging in the balance waiting for a trigger. Don’t be that trigger. It might not be the 1st person on the slope. The slab depth has increased over the weak faceted snow. Remember the facets were very reactive prior to the storm. Staying off of slopes steeper than 30 degrees and avoiding runout zones will be important today. A small slide into a terrain trap could be consequential. Additional snow and rain are forecasted to fall and winds could move snow at upper elevations increasing the load today. This snowpack will need time to adjust. Be patient and be on the lookout for recent avalanches, cracking and collapsing, signs that the snowpack unstable.

Natural avalanches on Sunburst that occurred during the storm Saturday.

Small avalanches and wind effect in along Seattle Ridge.

Avalanche Problem 2

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

Very high winds during the storm Saturday have loaded leeward slopes. In addition there is snow falling today and winds gusting into the 40s. Winds slabs are likely found along ridgelines as well as lower down slopes due to those high wind speeds on Saturday. Pay attention to cracking and hollow sounding snow. Wind slabs could be soft or hard depending on exposure to winds and if triggered could release a larger persistent slab lower down on the slope. Today is not the time to be pushing into steep terrain. Avoiding slopes greater than 30 degrees is recommended.

Wind loading on leeward slopes, Tincan.

Weather

Tue, December 5th, 2017

Yesterday was overcast with light rain and snow showers on and off throughout the day. Winds were easterly 15-25 mph with gusts as high as 60 mph. Upper elevations picked up an additional 2-5″ of snow and rain fell to around 1500′. Temperatures were as high as 40F at sea level and the mid to high 20s at upper elevations.

Today will be mostly cloudy with .4″ of water (4-6″ snow) forecasted to fall. Today will start warmer and cool a bit this morning bringing the snow level down. Winds will be easterly 10-20 mph gusting into the 40s.Tonight into tomorrow a stronger wave of precipitation is forecasted to impact the area. The model runs on this are still uncertain this morning, however looking into the future NWS says “Much more confidence exists in the forecast for Southcentral to remain well above normal for temperatures, and continue to deal with round after round of moisture from the subtropical Pacific. Stay tuned!

*Center Ridge SNOTEL is reporting erroneous temperature data. See Turnagain Pass DOT weather station for accurate temperature at 1000′.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	32*	0	.2	29
Summit Lake (1400′)	33	0	.3	9
Alyeska Mid (1700′)	34	0	.2	18

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	ENE	26	60
Seattle Ridge (2400′)	28	ESE	18	40

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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