Sat, January 18, 2014 Turnagain Pass Avalanche Forecast

Sat, January 18th, 2014

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

Avalanche activity from yesterday:

Yesterday’s heavy rain below 2,000′ and wet snow above 2,000′ combined with very warm temperatures induced a widespread natural avalanche cycle. This extened to the Summit Lake area as well. We were able to get video footage of one natural slide in Portage Valley – video below. Additionally, the AK DOT Avalanche Program was able to trigger several large avalanches along the Seward Highway – one these can be seen in a video HERE.

The start zones for much of yesterday’s activity was in the dry snow above 3,000’. These slides turned wet as they descended due to entrainment of wet snow below treeline. You can see in the video below from Portage Valley how the powder cloud dissipates as the debris encounters the wet snow.

The slightly cooler temperatures along with breaks in cloud cover overnight will help limit any natural acitivity today. Much of the pack below treeline was draining water rapidly yesterday and today there may be a slight refreeze on the surface. The main areas of concern for wet avalanches will be near and just below treeline or in a gully at sea level elevations where debris can be funneled.

Avalanche Problem 2

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

The shock of up to 3” of water weight in 24-hours yesterday did a number to the pack – as can be seen in the above videos and in our field day HERE. At the upper elevations this has added around 2′ of new snow along with rain on snow below treeline. The weak snow near the base of pack that is the culprit for many of our large avalanches is once again being overloaded. Though visibility was limited yesterday, it is likely that many of the debris piles seen occurred by an avalanche breaking near the ground and propagating across slopes at the mid to upper elevations.

For today, the weather has abated but don’t count on the weak snow near the ground to have adjusted to the new load yet. There is much uncertainty going into today but the fact remains that during the past 24-hours we have had a significant avalanche cycle and there are slopes likely teetering on the edge just needing a human trigger.

Additional Concern

Storm Slabs

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.

More info at Avalanche.org

At the upper elevations – above 3,000′ – temperatures were cold enough for around 2′ of snowfall during yesterday’s storm. Storm snow instabilities, mainly in the form of wind slabs are likely to be found and potentially triggered. With the warm temperatures these are likely to settle out within the 24-hour window – however, this is relegated to the storm snow and not the persistent slab issue mentioned above.

There is also the potentail for any storm snow avalanche to step down and trigger a larger slide breaking in the weak snow at the base of the pack.

Weather

Sat, January 18th, 2014

A fast moving and powerful storm moved through yesterday with rain below 2,000′ and heavy snow above. Ridgetop winds associated were from the East and averaged in the 50-60mph range with a max gust in the past 24-hours of 106. Temperatures at treeline were mainly in the upper 30’s and decreased to the low 30’s by the end of the precip.

Storm totals beginning Thursday night ending 6am this morning:
Turnagain Pass (1880′) – 2.2 € water, mostly rain (4 € wet snow)
Alyeska Mid (1700′) – Roughly 3-3.5 € water, mostly rain (5 € wet snow)
Summit Lake (1400′) – 1.3 € rain

Overnight the skies have broken slightly as the main portion of the system is now to our North. There is a section of clouds and precipitation that is being wrapped around the low center which may add another 1-3 € of snow today. This has colder air entrained so snow levels should drop to around 400′. Ridetop wind today will be from the Southeast and in the 20mph range. Temperature at treeline will be around 30F and sea level mid 30’sF.

Sunday, another low pressure system heads our way that looks to be somewhat similar to yesterday’s storm. Stay tuned.

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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