Sat, March 05, 2022 Turnagain Pass Avalanche Forecast

Sat, March 5th, 2022

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

Storm Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

Over the past three days there has been a big difference in the amount of new snowfall across our forecast area, with coastal areas like Portage and Placer receiving multiple feet of new snow and more inland areas like Turnagain Pass and Girdwood receiving less than a foot. Natural and human triggered avalanches are very likely in areas that received heavy snowfall, and the potential for remote triggering large avalanches exists because of a layer surface hoar that was buried underneath the new snow. The snowpack needs time to adjust to the large new snow load in these areas and travel in avalanche terrain is not recommended. Widespread avalanche activity was observed in the Spencer Bench area on Thursday and the added snowfall since then will have increased the likelihood of triggering and potential size of avalanches.

In areas that have not been favored by the recent snowfall, like Turnagain Pass and Girdwood, there has still been plenty of east wind to transport the new snow into wind slabs up to 2′ deep that are likely to be triggered by a person. The potential for buried surface hoar underneath the new snow could make triggering avalanches on lower angle slopes possible and produce avalanches with wider than typical propagation. In protected areas the depth of the new snow will determine whether storm slabs are possible to trigger today, with the likelihood increasing in areas with deeper snow totals. Another 2-6″ of new snow is expected today which will increase the potential for storm slab avalanches in protected areas and increase the snow available for wind transport. Using hand pits and test rolls is a great way to check how well the new snow is bonding to the old surface and determine if avalanches are possible in the area you are travelling.

Cornices: The new snow and strong winds over the past 24 hours will have added some fresh load to our existing cornices and could make them more sensitive to human triggers. With poor visibility expected today it is best to avoid spending time underneath areas with cornices because they could release naturally due to added wind loading.

Shooting crack on a wind loaded test roll in the treeline elevation band in the Crow Creek area. Photo 3.4.22

Only a few inches of new snow above a stout melt freeze crust at lower elevations in Crow Creek area yesterday. Photo 3.5.22

Additional Concern

Deep Persistent Slabs

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.

More info at Avalanche.org

In the far northern and southern portions of our forecast area (i.e. Crow Creek, Lynx Creek, Silvertip Creek) the snowpack is thinner and the potential for triggering a large avalanche on a layer of facets from November exists. Yesterday we found the November facets only 6″ down from the surface in a wind scoured area near Crow Creek. This was quite surprising and indicates that human triggered avalanches could be possible on this deeper weak layer if a failure is initiated in a thin spot of the snowpack. Recent avalanche activity on this layer has been associated with significant snowfall events and since these thinner snowpack areas of the forecast region have not received much snow the past three days the likelihood of an avalanche on this layer is relatively low.

Similar thin snowpack conditions exist in the Summit Lake area, which is outside our forecast zone, and triggering avalanches on deeper weak layers is more likely.

Wind scoured area along our skin track with less than 3′ total snowpack depth and weak facets only buried 6″ deep. Photo 3.4.22

Weather

Sat, March 5th, 2022

Yesterday: Overcast skies with light to moderate snow in some areas of the forecast zone. Turnagain Pass and Summit Lake got 0″ of new snow in the past 24 hours, Girdwood got 0.5″ of water which should be about 6″ of new snow, and Portage/Placer got 1.0″ of water which is about 12″ of snow. Snow line was between 500-1000′. Winds were very strong at upper elevations yesterday morning with averages in the 20-30 mph range and gusts into the 60-70 mph range. During the afternoon winds backed off slightly and are currently in the 15-25 mph range with gusts of 30-50 mph.

Today: Snowfall is expected throughout the area today. Turnagain Pass should receive 2-4″ of new snow, with Girdwood, Portage, and Placer expected to receive 4-6″. Snow line is expected to be between 900-1100′. Winds will be in the 15-25 mph range at upper elevations and will shift to westerly this evening as the snowfall ends. Temperatures will remain relatively warm, with upper elevations in the mid-twenties and lower elevations in the mid to upper-thirties.

Tomorrow: Sunday looks like clouds will clear up for the most part and winds will be light to calm during the daylight hours. No new snow is expected for a few days. Temperatures will drop into the twenties at sea level.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	0	0	92
Summit Lake (1400′)	34	0	0	39
Alyeska Mid (1700′)	31	6	0.5	NA

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	ENE	26	79
Seattle Ridge (2400′)	25	SE	17	34

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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