Wed, November 30, 2016 Turnagain Pass Avalanche Forecast

Wed, November 30th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

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

A low pressure system in the Eastern Gulf will combine with cool Northern arctic air over Southcentral Alaska today. There is a “fair amount of uncertainty on snow amounts” impacting Turnagain Pass, but expect snow totals to be anywhere between 5-15 inches. Moderate Easterly winds (10-25mph) are also expected which could easily increase the avalanche danger throughout the day especially if snowfall intensifies. It will be important to adapt your travel plans to changing weather conditions and be on the lookout for any signs of instability; shooting cracks, whumphing sounds, or recent avalanches.

Don’t forget what this snow is falling on. A reactive layer of buried surface hoar from Nov.16 lies below 1-2 feet of old snow. This widespread layer exists on all aspects and has been the culprit in dozens human triggered avalanches over the last two weeks including the most recent on Sunday Nov.27 in Seattle Creek area. Today’s weather has the potential to re-load this weak layer increasing the likelihood for human triggered avalanches. Slab depths could be as thick at 1.5-3 feet thick depending on snowfall amounts. Cautious route choices and conservative decision making will be essential today.

Buried surface hoar is still a very visible layer and continues to be reactive in tests pits. Photo taken at 3200′ on a SW aspect of Tincan on 11/27 by Aleph Johnston-Bloom

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

Today’s new snow will be falling on weak old snow; snow that has been ‘faceting’ due to cold temperatures this week. The combination of wind and the possibility of higher snowfall totals (up to 15″) could produce storm slabs 1’ thick both in the alpine and at treeline.

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Watch for glide cracks and remember to limit time under these, there have been a handful that released last week. *Several cracks have been opening in popular terrain like Tincan’s Common bowl and the SW face of Sunburst.

Weather

Wed, November 30th, 2016

Yesterday was cold and clear. Temperatures were in the single digits and light to moderate ridgetop winds made for a windchill of -5F to -20F below zero. Winds varied from North to Southwest and no new precipitation was recorded.

Today 5-15 inches of snowfall (up to 0.5 inches of water) is expected today in the upper elevations of Turnagain Pass. Temperatures will start out cold and warm up in to the 20F’s throughout the day. Easterly ridgetop winds are expected to be moderate (10-25mph.)

Tonight and tomorrow more snow is expected throughout the region. Its hard to say how much will impact our area, but temperatures are staying cool enough that it should all fall as snow.

***We are happy to report as of 3pm yesterday Sunburst Weather Station is back online!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	6	0	0	17
Summit Lake (1400′)	1	0	0	3
Alyeska Mid (1700′)	8	0	0	5

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	5***	Variable***	6***	27***
Seattle Ridge (2400′)	7	NW	11	39

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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