Wed, January 15, 2020 Turnagain Pass Avalanche Forecast

Wed, January 15th, 2020

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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

Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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

We have been talking about buried weak layers for a while. Let’s take a quick inventory of the state of the snowpack. It has now been two weeks since the New Year’s Eve storm and we have been in a mostly clear and cold weather pattern. Since that storm the soft surface snow has become faceted and recently we had almost a week of on and off wind. Due to the wind, the faceted surface snow was buried in some terrain by wind slab. The last human triggered avalanche was Friday evening in Crow Pass. Where does this leave us now in relation to triggering an avalanche? Well… It is still possible and something to keep in mind if traveling in steep terrain in the Alpine. The level of wind effect has been different across the advisory area. This is a key factor in where the most hazard is. If you find yourself in a zone with very hard wind effected snow this could be sitting on very weak faceted snow below. This is the suspected set up in the avalanche on Friday. Lingering wind slabs are now persistent slabs because they are associated with buried facets. Additionally there are layers deeper in the pack (Solstice buried surface hoar and/or facets and facets with the December 9th rain crust) that have been indicating that it would be hard to trigger them at this point but not impossible. The best way to manage this uncertainty is to avoid steep slopes with hard snow over soft snow, use safe travel protocol and think about consequences. If you did trigger a large avalanche where would all the snow go? Look for signs of instability but realize you may not see them with this type of avalanche problem.

Propagation in a snowpack test on Manitoba at 2700′ on a weak layer of buried facets, 1.11.20. Photo: Alaska Avalanche School Pro 1

Propagation in a snowpack test on Goat Mountain, 1.10.20. Photo: CNFAIC

Additional Concern

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

Loose snow avalanches (sluffs): On slopes out of the wind expect sluffing in steep terrain. The surface snow is becoming looser and looser by the day with the cold temperatures.

Cornices: Give cornices plenty of space and limit your exposure when passing beneath them.

Glide avalanches: Due to the unpredictable potential to release, limit your time spent under glide cracks.

Weather

Wed, January 15th, 2020

Yesterday: Skies were partly cloudy with patchy valley fog and very light snow showers. Temperatures were in the single digits to low teens. Winds were westerly 5-10 mph with gusts into the 20s. Overnight temperatures were mostly in the low single digits while a few stations recorded temperatures just below 0°. Winds were light and westerly.

Today: Mostly clear skies with temperatures in the low single digits. The winds are forecast to be light and becoming calm in the afternoon. Overnight temperatures look to be slightly inverted with temperatures in the the single digits at upper elevations and around 0° or just below in valley bottoms. Winds remain calm.

Tomorrow: Sunny skies, calm winds and temperatures in the single digits. This cold and clear pattern looks to persist into the weekend until skies become cloudy Saturday evening and with a chance of snow on Sunday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	6	1	0.01	38
Summit Lake (1400′)	4	1	0.01	15
Alyeska Mid (1700′)	7	4	0.04	37

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	4	W	8	22
Seattle Ridge (2400′)	6	W	2	16

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
12/02/23	Turnagain	Observation: Seattle Ridge	Schauer / Keeler Forecaster
12/02/23	Turnagain	Observation: Tincan South Side	Anonymous
12/02/23	Turnagain	Observation: Eddies up track	Luc Mehl
12/01/23		Avalanche: Sunburst	John Sykes Forecaster
12/01/23	Turnagain	Observation: Eddie’s trees	Anonymous
12/01/23	Turnagain	Observation: Turnagain – God’s Country	Graham Predeger Forecaster
11/30/23	Turnagain	Avalanche: Tincan Trees	Kakiko Ramos-Leon
11/27/23	Turnagain	Avalanche: Tincan Ridge	Schauer/ Stiassny Forecaster
11/26/23	Turnagain	Observation: Road report: Slide with dirt on Repeat offender	Anonymous
11/26/23	Turnagain	Observation: Pete’s North	Ben Sullender

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