Mon, February 17, 2014 Turnagain Pass Avalanche Forecast

Mon, February 17th, 2014

Alpine

Above 2,500'

3 - Considerable

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.

Avalanche Problem 1

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 late January onslaught of rain and high temps was followed by a period of clear and cold weather. At the tail end of this January storm a small amount of snow fell in the higher elevations. That thin layer of snow sat on a stout slick crust for almost ten days. During that time this layer grew weak. Between Feb 7th and today over 36” of snow has fallen on top of this weak layer in the higher elevations. In areas where this weak layer exists, mainly above 3,000’ and in some places above 2,000′, the potential for slabs up to 3’ in depth could release from the weight of a person.

This issue is a tricky one to detect. Because the distribution of this weak layer is not uniform, it is difficult to know with confidence whether that weak layer is lurking below you or not. It should be assumed that this combo is present above 3,000’. This problem reared its ugly head yesterday with multiple parties reporting remotely triggered avalanches throughout the forecast area. Click for Eddie’s avalanche, Twin Peaks avalanche & Tenderfoot (Summit Lake area) avalanche.

Eddie's remote

The best way to manage this problem today is to simply avoid terrain over 35 degrees in the higher elevations. You might be able to get away with skiing steeper terrain, but it is a roll of the dice given the current conditions.

Avalanche Problem 2

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

Another modest batch of precipitation will refresh the riding conditions. It will also require being on the lookout for issues related to storm snow instabilities.

Loose snow avalanches
These will be generally low volume but easy to trigger in terrain over 40 degrees. This problem is one that becomes more serious when traveling above terrain traps such as trees, gullies and cliff bands.

Storm Slabs & Wind Slabs
It will be possible for humans to trigger newly formed slabs in steep terrain today. Winds have been relatively light but enough to create new slabs up to a foot in depth. Sticking to terrain 35 degrees and under, especially on leeward upper elevation slopes will be the best way to avoid this problem today.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Cornices continue to grow and build above many starting zones. Give cornices a wide berth when traveling along ridge crests. Pay attention to the terrain above you as well. If you find your group below cornices spread out and only expose one person at a time.

Weather

Mon, February 17th, 2014

In the past 24 hours the mountains around Eastern Turnagain Arm have picked up ~5 € of new snow with ~.3 € of snow water equivalent. Ridgetop winds have been out of the East at 12 mph with gusts to 38 mph. Ridgetop temps have averaged in the single digits F and have been gradually climbing overnight into the low teens F.

Today expect snow showers to continue through the morning hours with potential for clearing skies by the afternoon. Snow accumulations of 2-4 € are possible. Winds will be light out of the East at 5-10 mph. Temperatures at 1,000′ will climb into the high teens to low twenties F.

The massive upper level Low pressure system that has been parked over much of the state will continue to bring alternating bands of precip and clear skies until tomorrow. That system will begin to break down beginning late tomorrow. Expect more precip and rising temperatures as we head into the middle part of the week.

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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