Sun, February 02, 2020 Turnagain Pass Avalanche Forecast

Sun, February 2nd, 2020

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.

Recent Avalanches

Yesterday two skier triggered avalanches were reported. In one incident a skier triggered but was not caught in a a small wind slab avalanche in the trees at Tincan. The avalanche was estimated at 50-60′ wide with a crown depth up to 9″ thick, and ran approximately 50-60′ vertically.

Another slab avalanche was reported near Girdwood. The rider and partners avoided the runout. The slab depth was estimated to range from 8”-24” thick and ran 60′ down the slope.

We’re grateful for the positive outcomes, and to the groups for sharing their information.

Skier triggered avalanche near Girdwood. 2.1.20 . Photo: Anon.

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

Our loose snow from earlier in the week moved around in many places from yesterdays northwesterly outflow winds. This trend of wind transported snow will continue as a storm is forecast for this evening. Although the outflow winds were from the northwest, and the impending storm is calling for southeast winds, it can be difficult to predict which slopes have formed wind slabs. Where windslabs exist on steeper slopes, it could be easy for a human to trigger an avalanche. Small steep wind effected slopes are still suspect. Because of this, it’s essential to look for clues where wind slabs are forming, or have already formed. If you see the winds depositing snow onto the lee of ridges or gullies, that’s a clear indicator a slab could be forming. Where visibility is low or you can’t see your entire route, remain aware of the snow beneath you – you could be entering a wind slab if you feel stiffening of the snowpack, see shooting cracks, or sense hollow drum-like sound in the snow. Any of these signs are cause for reconsidering your route.

Snow transporting along Seattle Ridge. 2.1.20 . Photo: A Dahl

Cornices: Cornices continue to form and could be touchy to human trigger as they build with transporting snow. As always, give cornices a wide margin.

Avalanche Problem 2

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

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

Our snowpack structure contains weaknesses formed before the storms earlier this week. The recent incremental loading from new snow and wind transported snow managed to naturally trigger these weaknesses earlier in the week. Although the snowpack is adjusting to this new load, it remains possible for a human to trigger these layers 2-3′ down in the snowpack. These layers could be easier to trigger in shallow areas and near rocky outcrops. If a wind slab is triggered, it could step down to trigger one of these layers deeper within the snowpack.

Loose Snow Avalanches: On steep slopes with unconsolidated snow, watch for easily triggered loose snow sluffs.

Weather

Sun, February 2nd, 2020

Yesterday: Mostly clear skies with cold northwesterly winds. These outflow winds blew generally in the 20-30mph range with areas toward Seward seeing higher speeds. Temperatures along ridgelines were in the -10 to 0°F range while lower elevations remained mostly in the single digits.

Today: A strong low-pressure system heads into Southcentral Alaska today and will bring cloud cover, strong southeast winds, and a chance for some snowfall this afternoon into the evening. Temperatures are predicted to reach up to 16°F with southeast wind 5 to 15 mph increasing to 30 to 40 mph in the afternoon. Accumulations range from 1-3″ in the Girdwood and Turnagain pass areas, and up to 8″ in the Portage valley.

Tomorrow: Mostly cloudy skies with a high near 25°F and low around 21°F. Light snow is expected throughout the day. Winds will be out of the east ranging from 30 to 35 mph, shifting to north winds 5-10 mph in the evening.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	7	59
Summit Lake (1400′)	-1	20
Alyeska Mid (1700′)	5	55

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	-1	W	9	24
Seattle Ridge (2400′)	4	VAR	8	22

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

Riding Areas

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