Sat, March 02, 2024 Turnagain Pass Avalanche Forecast

Sat, March 2nd, 2024

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

Sun, March 3rd, 2024

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

Sun, March 3rd, 2024

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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

A skier triggered avalanche at 2800′ near Bench Lake in Johnson Pass was reported yesterday, with no one caught or carried by the slide. The avalanche was triggered by the 4th skier on the slope and released roughly 2′ deep and 75′ wide. Based on the size of the avalanche and the fact that it was the 4th skier on slope that triggered it, there is a good chance it released on some kind of buried persistent weak layer. The overall snow depth in this area is roughly 3′ deep, which is much thinner than Turnagain Pass. The Johnson Pass area has very few observations from this season but based on the overall snow depth we think the snowpack structure is more similar to Summit Pass and the Central Kenai mountains.

Avalanche Problem 1

Wind 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

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.

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

The northwest outflow winds that have been impacting the region for the past several days are expected to diminish today. Some strong gusts are expected to continue along Turnagain Arm and other favorable gap wind locations, but for most of the forecast area winds are expected to be light. It will still be possible to find a lingering wind slab around 1′ deep after the past few days of strong winds. Areas where stubborn wind slabs tend to be a problem are in steep terrain near ridgelines, gullies, or convex rollovers. Keep an eye out for shooting cracks and hollow feeling snow on the surface to identify terrain where human triggered wind slabs are still possible. Using small test slopes to check for shooting cracks is a great way to evaluate how sensitive wind slabs are before committing to steep terrain.

Loose snow avalanches are likely today if you can find a sheltered location that still has soft snow on the surface. Dry loose avalanches or sluffs will be easy to intiate in steep terrain and could pick up momentum and run further than expected. On steep southern aspects near rocks or exposed vegetation wet loose avalanches are also possible if the sun warms up the snow surface enough today.

Cornices have been building during the windy conditions over the past few days and the sunny skies today could cause some natural cornice failures. Try to avoid spending time underneath cornices that are in the sun and be aware that it can be easy to accidentally get too close to the edge of a corniced ridge.

Firm and hollow sounding wind affected snow along a ridge just above treeline where lingering wind slabs could be an issue today. Photo 2.29.24

Additional Concern

Persistent Slabs

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.

More info at Avalanche.org

In the Johnson Pass area and further south towards Trail River the snowpack is generally thinner and weaker compared to Turnagain Pass. The large skier triggered avalanche reported yesterday at 2800′ above Bench Lake is a clear indication that buried weak layers are still an issue in these thin snowpack zones. If you plan to travel into the southernmost portion of the forecast area today check out the Summit Pass and Central Kenai mountains avalanche outlook for more information about recent avalanche activity and snowpack conditions in these areas.

Weather

Sat, March 2nd, 2024

Yesterday: Mostly sunny skies, with a period of overcast cloud cover moving through the area for a few hours midday. Temperatures were in the single digits to low teens F at low elevations and negative single digits F at upper elevations. Winds averaged 0-10 mph from the NW with gusts up to 20 mph in Turnagain Pass. Similar wind speeds were observed along Turnagain Arm, with slightly higher gusts up to 25 mph. No new snowfall.

Today: Another clear and cold day is expected with temperatures in the negative to positive single digits F. Winds should calm down today with averages of 0-5 mph from the N and gusts of 10 mph. In gap wind areas like Turnagain Arm stronger gusts up to 20-30 mph from the N are likely. No new precipitation is expected.

Tomorrow: Cloud cover is expected to gradually increase throughout the day tomorrow, which will also bring warming temperatures. Temperatures are expected to start out near 0 F and rise to the teens F later in the day. Winds should shift to the southeast and remain light at 0-5 mph with gusts of 10-20 mph. There is a chance of some snow shower in the evening, but no significant accumulation is expected.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	4	88
Summit Lake (1400′)	2	46
Alyeska Mid (1700′)	6	88
Bear Valley – Portage (132′)	11	–
Grouse Ck (700′)	8	66

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	-4	W	7	18
Seattle Ridge (2400′)	-1	N	3	11

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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