Fri, March 31, 2023 Turnagain Pass Avalanche Forecast

Fri, March 31st, 2023

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

Sat, April 1st, 2023

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

Sat, April 1st, 2023

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

There were no new avalanches reported yesterday. The last human-triggered avalanche was a large remote-triggered avalanche north of Girdwood on Tuesday. That was just the latest in a string of very large human-triggered avalanches in the area in the past week.

Avalanche Problem 1

Deep Persistent Slabs
N E S W NW NE SE SW

Aspect/Elevation
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.

Aspect/Elevation of the Avalanche Problem

Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

Despite another day of quiet weather on tap today, we are still dealing with dangerous avalanche conditions. The weak snow that was buried by the series of storms starting on 3/14 has not changed much, and it is still possible to trigger a very large avalanche. This layer is 3-6′ deep on average, and has produced large avalanches as recently as Tuesday. Part of the reason we haven’t seen more activity this week is just because there haven’t been as many people out since last weekend, when we saw multiple very large human-triggered avalanches.

This deep slab problem is really hard to predict, and impossible to manage beyond just avoiding traveling on or below steep terrain. It’s frustrating because now is the time of the season when we’re usually trying to get into bigger terrain, but the snowpack is just too dangerous right now. The problem layer is too deep to get any reliable test results, but we have found that weak structure in every pit we have dug since last weekend – most recently in four different pits between Magnum and Cornbiscuit yesterday (details here).

We have seen the size of avalanches this setup is capable of producing, and it is scary. It is going to take some time to heal, so for now all we can do is be patient and avoid steep terrain.

Wind Slabs: With another day of light to moderate winds, it is likely we will be able to find small but reactive wind slabs in upper elevation terrain. Be on the lookout for stiff snow on the surface, especially right below ridgelines, convexities, and in steep gullies.

Glide Avalanches: We have seen increased glide activity in the past week. These avalanches are very large and entirely unpredictable, so be sure to limit the time you spend traveling below them.

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Weather

Fri, March 31st, 2023

Yesterday: Light snowfall finished in the morning with clouds breaking up in the afternoon. High temperatures were in the mid to upper 20’s F at upper elevations, and in the low to mid 30’s F at lower elevations. Winds were light out of the east in the morning, switching westerly in the afternoon.

Today: Skies will be partly to mostly cloudy with high temperatures in the mid 20’s to low 30’s F and overnight lows dropping into the mid teens to 20 F. Light westerly outflow winds will pick up steadily during the day, but should stay around 5-10 mph with gusts of 10-20 mph. No precipitation is expected.

Tomorrow: Northwest winds will pick up slightly tomorrow, blowing 10-20 mph with gusts of 15-25 mph. High temperatures will be in the low 20’s to 30 F with lows in the low to mid teens F. Skies should be partly to mostly sunny, and no precipitation is expected.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	0	0	95
Summit Lake (1400′)	29	0	0	47
Alyeska Mid (1700′)	N/A	N/A	N/A	N/A
Bear Valley – Portage (132′)	35	tr	0.2	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	NE-NW*	4	12
Seattle Ridge (2400′)	23	E-NW*	3	8

*Winds shifted directions yesterday evening.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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