Sat, January 30, 2021 Turnagain Pass Avalanche Forecast

Sat, January 30th, 2021

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

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.

Recent Avalanches

A skier triggered a storm/wind slab avalanche yesterday on one of the lower Eddies rollovers. The avalanche had wide propagation and is suspected to have run on the buried surface hoar/near surface facet layer that was the surface snow from last week. This layer sits just under the new snow from the past few days. No one was caught and the slab broke just under the skier who triggered it. More details on the report linked above.

Section of the crown that was triggered on Eddies yesterday. 1.29.21. Photo: Ryan S.

A wider angle look at the avalanche showing the significant propagation. 1.29.21. Photo: Ryan S.

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

It’s going to be a HEAD’S UP sunny day out there. Not only are there tricky avalanche conditions, but we can expect a busy Saturday in the backcountry. We need to be clued into a few simple things. First, for the first time in weeks 8-16″ of new snow fell on a weak layer of buried surface hoar and near surface facets. Second, the new snow is so loose it’s not necessarily forming a slab everywhere, but where it is, avalanches like the one above from Eddies will be possible to trigger. Third, remember our safe travel protocol; exposing one person at a time, watching our partners, having escape routes planned and being patient if others are on the slope ahead of you.

The good news is, these avalanche issues are right at the surface. Additionally, winds during the snowfall were generally moderate from the NE, so wind slabs may not be as prevalent as with other storm events. That said, although the weak layer is there, it’s whether a slab has formed that’s the question. If you are headed out today watch for:

How much new snow fell in the area you are in? The more snow the larger the potential avalanche.
Is the snow slightly stiff and slabby? Or so loose it just crumbles in your hand?
Are there signs of wind loading? If so, expect a slab to be present. It could be much thicker due to the loading.
Do you see any cracking in the snow around your machine, board or skis?
What about any recent avalanches?

For those folks thinking about getting into the big terrain, soft wind/storm slabs may be found not only along ridgelines but lower on the slope. Even a small slab triggered could entrain a large degree of snow if the slope is steep and sustained.

Estimated storm snow totals at the mid-elevations:
North end of Turnagain Pass: 10-16″
South end of Turnagain Pass: 6-8″
Upper Girdwood Valley: 10-14″
Summit Lake: 1-2″
Portage/Placer Valley: 12-18″

Loose snow avalanches (sluffs): Sluffs are likely to be high volume and fast running. They could entrain not only all the new snow, but a portion of the facets that sit below it.

Cornices: As always, give cornices a wide berth and limit exposure under them. They continue to grow and peel along the ridgelines.

Additional Concern

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

Keep your eyes peeled for any new glide cracks. With the clearing skis we may see more of them opening up. Glide cracks can release into avalanches at anytime. They are completely unpredictable and can be very destructive. There are a few cracks on the SW faces of Eddies, Tincan and Manitoba ridges as well as the roadside of Seattle Ridge. Let us know if you see any new cracks or releases.

Weather

Sat, January 30th, 2021

Yesterday: Light snowfall and mostly cloudy skies were over the area. Turnagain Pass picked up around 3″ of new snow in the past 24-hours and just a trace in Girdwood and Summit Lake. Ridgetop winds were light to moderate along ridgetops, averaging 5-10mph from the northeast. Temperatures bumped up midday to the mid 20’sF along ridgelines, but have cooled back to the high teens overnight. At sea level, temperatures that were near 30F have also cooled to the low 20’sF.

Today: Mostly clear skies with some valley fog is forecast as yesterday’s system heads out and a high pressure ridge builds in. Ridgetop winds look to shift to the northwest and average in the 5-15mph range. Temperatures are on a slow decline as the northerly flow pushes in cold air. Sea level temperatures look to hover near 20F while valley bottoms and ridgelines drop to the low teens.

Tomorrow: Mostly sunny skies with very cold temperatures are expected for Sunday. Models are suggesting there is potential for a strong NW wind event for Sunday into Monday. Stay tuned and cross your fingers the winds stay quiet.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	25	0.2	3	128
Summit Lake (1400′)	20	tr	tr	43
Alyeska Mid (1700′)	23	0	0	111

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	NE	8	17
Seattle Ridge (2400′)	21	N/A*	N/A*	N/A*

*Seattle Ridge anemometer (wind sensor) is rimed and not reporting data.

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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