Mon, March 22, 2021 Turnagain Pass Avalanche Forecast

Mon, March 22nd, 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

We received a report of a large human triggered avalanche in Ragged Bowl from a party on Goat yesterday. They thought it had occurred around 4 pm yesterday and was likely a wind slab failing on a persistent grain (weak snow). Please let us know if you have more information on this by sending in an observation or dropping a note to staff@chugachavalanche.org.

Ragged Bowl avalanche, 3.21.21. Photo: George Creighton.

Avalanche Problem 1

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

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

The definition of MODERATE avalanche danger includes: Heightened avalanche conditions on specific terrain features. For now our snowpack sits in that box. Steep, unsupported slopes that have been recently wind-loaded warrant extra caution. The avalanche on Raggedtop, that we believe was triggered yesterday, fits into that category. In addition, observers are still reporting large whumpfs and there were human triggered avalanches on Thursday and Friday. These avalanches failed on buried facets and/or buried surface hoar in the top 1-3′ of the snowpack. On the flip side many people were out across the forecast area enjoying the sunshine with no incident yesterday. This conflicting data can be a bit confusing but is really indicative of a persistent slab issue. The bottomline is if you are heading out for some sunshine today, finding a spot where there is a slab over the buried weak snow remains a concern. The most likely place to run into trouble will be in terrain that has been recently wind-loaded, with stiff snow sitting on top of soft snow. Steep southerly aspects, where there are weak facets above and below a sun crust, may be more sensitive if there is enough of a slab over the crust facet combination.

Please watch for signs of instability, use good travel protocol, and think about terrain consequences.

Sluffs: Steep slopes that have been sheltered from the wind have around a foot or more of loose snow sitting on top of firm surfaces. It will be easy to trigger dry loose avalanches today, and they can pick up enough volume and speed to carry a person. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

Sun effect: Be on the lookout for sun effect on steep southerly slopes, especially under rocky areas at lower elevations. Watch for the surface snow becoming moist and small roller balls.

Small slab failing easily on facets above and below the sun crust yesterday, 3.21.21, on a southerly slope of Colorado Peak in Summit.

Weather

Mon, March 22nd, 2021

Yesterday: Sunny skies with northwest winds 5-10 mph and temperatures with highs in the teens to high 20°Fs. Overnight skies were clear and winds remained light. Temperatures were inverted with ridgetop temperatures in the teens and valley bottoms a few degrees below zero.

Today: Mostly sunny skies becoming partly cloudy in the afternoon with easterly winds 5-10 mph, gusting into the 20s. Temperatures will be in the teens to high 20°Fs. Increasing clouds overnight with a chance of light snow showers. Temperatures will be in the teens and winds will be easterly winds 10-20 mph with gusts into the 30s.

Tomorrow: Cloudy with snow showers in the morning becoming mostly sunny by the afternoon. Temperatures in the 20°Fs and light variable winds in the morning shifting to the west, 5-10 mph in the afternoon.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	15	112
Summit Lake (1400′)	12	45
Alyeska Mid (1700′)	13	114

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	10	W	8	21
Seattle Ridge (2400′)	12	N	3	19

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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