Fri, December 04, 2015 Turnagain Pass Avalanche Forecast

Fri, December 4th, 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

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

For almost a week now intermittent snow showers have added a welcome 8-12″ of low density snow at the mid-mountain elevations. Another round last night added 2-3″ of this. Snow quality continues to be reported as “excellent” – especially above treeline where “dust-on-crust” conditions disappear. Winds have been light over the past few days and are expected to be light again today, however, with such loose snow available for transport, keep in mind it can be blown into slabs easily. Otherwise, watch for sluffing on steep slopes.

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

How is the ‘snowpack structure’ looking as a whole? In general, pretty good. However, we are tracking a layer of old faceted snow that sits near the ground. This layer is likely responsible for some very sizeable natural avalanches during the Thanksgiving weekend storm, yet signs point to the layer adjusting since then and becoming unreactive. Until we gather enough data to rule this potential weak layer out, it’s something to keep in mind.

Weather

Fri, December 4th, 2015

Generally mild weather has been over us for the past 6 days. We have seen light Easterly winds, isolated snow showers and temperatures in the mid 20’s F on the ridgetops and near freezing at sea level.

Overnight, a quick moving disturbance added roughly 2-3″ of light snow at Turnagain Pass and Summit Lake while Girdwood Valley looks to have seen around 4″. Winds are light and variable currently and slated to turn back Easterly in the 5-10mph range today. Skies should be partly cloudy this morning before filling back in later today with a chance for another 1-2″ of low density snow this evening. Temperatures have dropped to the lower 20’s F on the ridgetops where they should remain today.

This weekend looks to be nice with partly cloudy skies, temperatures in the 20’s F and light winds. Stay tuned.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	26	2	0.2	25
Summit Lake (1400′)	24	2	0.2	12
Alyeska Mid (1700′)	27	3.5	0.25	20

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	NE	5	16
Seattle Ridge (2400′)	24	N/A	N/A	N/A

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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