Wed, February 10, 2016 Turnagain Pass Avalanche Forecast

Wed, February 10th, 2016

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

Cornice
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Cornices throughout the advisory area are very large and have the potential to be quite hazardous. A skier yesterday reported being caught off guard when one broke farther back than expected. Cornice fall can trigger avalanches on the slopes below or take you for a high consequence ride if you happen to go down with one in a bad spot. Give them a wide berth on ridgelines and limit time spent below.

Wind slabs: It will be possible to trigger old wind slabs on steep leeward slopes today. As the storm moves in with additional snow and wind, this may create new tender wind slab and add weight to already wind-loaded areas. Look for cracking, listen for hollow sounds and avoid stiff, pillowed snow.

Skier triggered cornice fall in Warm-up Bowl (-1 Bowl) yesterday. Photo: Wendy Wagner

Avalanche Problem 2

Glide Avalanches
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Size of Avalanches

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

We’ve still have literally hundreds of glide cracks littering the mid-elevations in and around Turnagain Pass. Many of these may not release at all, but we continue to see large and destructive glide cracks avalanching in or adjacent to popular ski terrain. Glide cracks are also widespread in high use snowmachine terrain and may release there just as easily! The bottom line is that they are completely unpredictable. It is best to minimize your exposure to this avalanche problem by avoiding time spent below glide cracks.

Glide cracks in Main Bowl (1st Bowl). Photo: Wendy Wagner

Additional Concern

Persistent Slabs

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

More info at Avalanche.org

We are still not ready to say goodbye to the possibility of triggering a persistent slab in the periphery of our core advisory are. Observations Monday from the Lynx Creek drainage (South of Turnagain Pass) found a layer of buried surface hoar (BSH). Likely deposited during the high-pressure weekend of Jan.30/31, it’s now buried by a 2-3’ slab. This one data point Monday showed the BSH to be unreactive. That is good news, but given the nature of persistent weak layers, we are not comfortable saying this is not going to be a problem. We just don’t have enough information and this is a low probability, potentially high consequence set-up. There is still a chance of triggering an avalanche similar to the one in Groundhog Creek on January 30th, which luckily did not catch anyone. Ride slopes one at a time, park and regroup in safe areas and look for cracking and collapsing while traveling.

Weather

Wed, February 10th, 2016

Yesterday started off partly cloudy and progressed to clear skies and lots of sunshine by the afternoon. Winds were light from the NE. Temperatures were in the mid-20Fs to mid-30Fs. There was a distinct warming period in the afternoon.

Today will be mostly cloudy with a chance of rain and snow showers increasing throughout the day. 1-2″ of snow is forecasted. The rain/snowline is expected to be around 1100′. Temperatures will be in high 20Fs to mid 30Fs. Winds will be Easterly, 10-20 mph with the potential for higher gusts.

Precipitation will increase overnight and the temperatures and rain/snowline will rise as the next warm, moist series of low pressure systems dictate the weather pattern.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	0	0	107
Summit Lake (1400′)	30	0	0	31
Alyeska Mid (1700′)	30	0	0	92

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	NE	10	31
Seattle Ridge (2400′)	27	n/a	n/a	n/a

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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