Fri, January 01, 2021 Turnagain Pass Avalanche Forecast

Fri, January 1st, 2021

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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

Wind Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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

Blue skies, light winds and chilly temperatures are on tap for this New Year’s Day; what a great weather forecast to bring in the New Year and not to mention, we have 13 more minutes of daylight since solstice! With nothing weather-wise to increase the avalanche danger, we are looking at a few existing snowpack issues that should keep us on our toes. These are lingering wind slabs and some funny business buried in the snowpack, discussed below.

First wind slabs. Over the past 10 days the mountains have received quite a bit of wind. Winds have been from our standard easterly direction and the most recent winds that formed slabs were two days ago. Hence, wind slabs, wind crusts and scoured areas are common above treeline. With folks headed into the further reaches of the forecast zone and beyond, there are sure to be a few wind slabs that could still pop out on us. Watch for hard snow over softer snow and any cracks that shoot out from you. Wind slabs generally have a smooth rounded surface where snow has been piled up. Be suspect of these pillowed areas on the steep slopes, rollovers and in steep gullies.

In addition, on steep slopes with only loose surface snow, keep an eye on your sluff, as usual. Also, don’t trust cornices. Always give them a wide berth and limit time under them

Wind effect on Pyramid Pk at Turnagain Pass. Soft snow can be found, but there is definitely a high degree of hard wind packed snow in the Alpine zones. 12.31.20. Photo: Peter Wadsworth

Old natural wind slab avalanche in one of the Seattle Ridge headwall chutes. 12.31.20.

Avalanche Problem 2

Deep Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and 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

As we’ve been mentioning for several days now, at the mid elevations (1,000 – 2,500′) there is the old December 1st crust that continues to degrade. It is 3-5′ below the surface and between 1-4″ thick. It is slowly metamorphosing (changing) from a strong crust into a faceted weak layer and crust combination. This is happening quicker in some areas than others. For example, we’ve found it more concerning on the non-motorized side of Turnagain Pass and in Girdwood Valley. Just yesterday, this crust/facet combo was the culprit in another large 6′ deep explosive triggered avalanche in Girdwood Valley. Although it is still unlikely a person could trigger one of these large slabs at these mid-elevations, we need to keep it on our radar. Whumpfing will be a sure sign you’ve found some weak snow beneath your feet.

A lot of folks have been getting out in the Summit Lake region to the south of our forecast area. Here, not only is this December 1st crust/facet combo a concern, but other mid-pack weak layers and even the basal facets on the ground in the Alpine continue to show weaknesses. In general, the snowpack is thinner and weaker and along with other shallow zones (Silvertip for example) it is worth keeping these old weak layers in mind before pushing into bigger terrain.

Weather

Fri, January 1st, 2021

Yesterday: Mostly sunny skies were over the region. Ridgetop winds were generally light from the east (5-10mph) with a few stronger gusts. Temperatures were inverted with the clear skies- teens in valley bottoms and parking lots, with mid/upper elevations being near 20-25F.

New Year’s Day: Clear skies are on tap for the New Year. Ridgetop winds are expected to be light from the east (5-10mph). An inversion is in place this morning that should remain through the day- valley bottom temperatures are in the 10-15F range while mid and upper elevations are near 20F.

Tomorrow: Another blue sky day is forecast for Saturday with light easterly ridgetop winds and temperatures in the teens. Sunday skies remain mostly clear and winds switch to a more off-shore northwesterly flow and we’ll be watching for any increase in them. The ‘record setting’ low pressure over the Aleutians will move into the Gulf sometime early/mid-week, stay tuned!

*Ridgetop weather stations stopped reporting at midnight. We are working to get them back on line asap.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	24	76
Summit Lake (1400′)	18	31
Alyeska Mid (1700′)	24	80

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	NE	7	14
Seattle Ridge (2400′)	20	SE	5	11

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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