Thu, February 26, 2015 Turnagain Pass Avalanche Forecast

Thu, February 26th, 2015

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

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

As we move away from the most recent loading event last weekend the likelihood of triggering an avalanche is on the decline. A well-documented weak layer of facets beneath a 1-3’ slab can still be found, it has not disappeared, but the stability appears to be improving with time. No new weather events have added additional stress in the last five days and the lack of obvious instability (like no recent avalanches or widespread collapsing) point towards the weak layer slowly adjusting to its load. In test pits however, we are still finding a high likelihood of propagation, and if enough force is applied in just the right spot it could initiate a high consequence avalanche.

This can be a tricky problem to manage in our heads as we find snow conditions in the Alpine feeling very much like the dense Chugach powder we so often associate with a stable Maritime snowpack. Just because someone skied a steep slope does not mean steep slopes are safe. Careful snowpack evaluation is recomended; getting a closer look underneath the slab could help remind you that a weak layer is lurking below.

Triggering a slab will be more likely on well-connected steeper slopes (> than 35°.) Trigger points are likely to be in thinner areas of the snowpack near rocks and along convexities of steep rollover features.

Be sure to practice safe travel habits. Constantly identify safe spots, move between islands of safety one at a time, and always have an escape zone in mind.

Additional Concern

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

Today daytime temperatures and expected to be in the mid to high 30’s and if cloud cover or fog roll in, this could increase the insulating affect and start breaking down the surface crust below 2500’. If you find warm temps causing you to sink into bottomless loose snow, avoid steep terrain where wet avalanches might be possible. This avalanche concern is unlikely, but is worth mentioning as our thin mid elevation snowpack battles with spring like conditions.

The photo below was taken from the uptrack at Seattle Ridge yesterday as a dense valley fog began lifting late in the afternoon.

Weather

Thu, February 26th, 2015

Yesterday a thick valley fog burned off later in the day and winds were calm. Temperatures were in the mid 20’s F most of the day with a spike mid day in the low 30’s F at mid elevations.

Overnight temperatures dropped into the low 20’s F. Ridgetop winds were 10 mph out of the Southwest on Seattle Ridge. No new precipitation was recorded in the last 24 hours.

Today skies will be mostly sunny at higher elevation, and patches of valley fog are likely along Turnagain arm. Temperatures will be warm, in the mid 30’s F along ridgetops, with light to moderate winds out of the Southeast. Tonight cloud cover should move in and temperatures look to remain warm throughout the evening.

Our next chance for precipitation is Friday night into Saturday as a low-pressure system tracks in our direction from the Aleutians.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	24	0	0	40
Summit Lake (1400′)	22	0	0	6
Alyeska Mid (1700′)	24	0	0	23

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	20	N/A	N/A	N/A
Seattle Ridge (2400′)	20	Var.	4	12

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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