Thu, February 11, 2021 Turnagain Pass Avalanche Forecast

Thu, February 11th, 2021

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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.

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

More blow than snow…? Say it ain’t so… Unfortunately that appears to be the current situation. Easterly ridgetop winds have jumped up and are averaging in the 30s and 40s, with Sunburst recording a gust of 71 mph this morning. If you are thinking of heading out today, expect quite windy conditions and increasing avalanche hazard. Yesterday winds did not blow as high as forecast but were strong enough to move snow around in wind exposed terrain. Observers reported shooting cracks and touchy, shallow wind slabs. They also noted plenty of soft snow left to move around. With strong winds that ramped up last night forecast to continue today and continued snow showers, we expect the slabs to build even more, be easily triggered by a person on skis or machine and potentially release naturally. This means that paying attention to what terrain above you is also important.

What to watch out for if you’re headed out today:

Areas with current wind-loading (winds should blow all day, peaking this afternoon)
Slabs lower on slopes from cross-loading (Seattle Ridge is a good example)
Stiff snow over softer snow (punchy snow)
Cracks shooting from your skis or machine
Whumpfing (collapsing of the snowpack into the faceted snow underneath)

Remember, expect any wind slab you find to be sitting on weak faceted snow and/or surface hoar and poor bonding is likely. There is also still a chance a persistent slab avalanche could be triggered. There is an older layer of buried surface hoar that is sitting under old wind slabs from the NW wind event last Saturday. A wind slab triggered today may be able to step down to this layer and cause a deeper avalanche.

Sluffs: If there are steep slopes out of wind, watch your sluff. These continue to be easily triggered and high volume in steep sustained terrain.

Cornices: Cornices are large and strong winds today will be adding additional stress. Cornice falls may trigger wind slabs on the slope below. Give them extra space as they can break farther back onto a ridge than expected and limit exposure under them.

Cracking on a wind-loaded slope yesterday on Tincan, 2.10.21

Soft snow over buried surface hoar in mid-elevation pit on Tincan yesterday, 2.10.21. This set-up could be quite touchy with a more developed slab.

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

Glide cracks are unpredictable, not associated with human triggers, and can release without warning at any time. New glide cracks are opening up around our region and existing ones are on the move. The most recent glide crack to avalanche was two days ago on Penguin Ridge. The best way to manage this problem is to avoid traveling on slopes directly below glide cracks.

Weather

Thu, February 11th, 2021

Yesterday: Skies were mostly cloudy with a few pockets of blue in the afternoon. Winds were easterly 5-15 mph gusting into the 20s. Temperatures were in the high teens to mid 20°Fs at upper elevations and mid 30°Fs at sea level. There were light snow showers on and off throughout the day with 1-2″ of accumulation. Overnight skies were cloudy with light snow showers early this morning. Winds were easterly 20-40 mph gusting into the 50-60s with Sunburst hitting 71 at 4 am this morning. Temperatures were the teens to low 20°Fs at upper elevations and low 30°Fs at sea level.

Today: Skies will be mostly cloudy with light snow showers in the forecast, trace-3″ possible. Temperatures will be in the teens in the Alpine and the high 20°Fs to mid 30°Fs at lower elevations. Winds will be easterly 20-40 mph gusting into the 50s and 60s. There is some uncertainty with the wind models today so they may be lower than forecast, as was the case yesterday. Overnight snow showers and strong easterly winds continue and then taper off around midnight. Temperatures will be in the teens and 20°Fs.

Tomorrow: Skies will start off cloudy and become mostly sunny in the afternoon. Winds will be light and easterly and temperatures will be in the teens at upper elevations and high 20°Fs at sea level. The sunshine, light winds and moderate temperatures look to continue on Saturday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	27	2	0.2	117
Summit Lake (1400′)	27	0	0	43
Alyeska Mid (1700′)	25	2	0.17	109

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	16	NE	19	71
Seattle Ridge (2400′)	20	E	16	33

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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