Wed, December 25, 2013 Turnagain Pass Avalanche Forecast

Wed, December 25th, 2013

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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 generally poor structure to our snowpack is keeping the persistent slab our primary concern again today. Avalanche activity appeared to peak on Sunday with two human triggered avalanches in the Turnagain area. Cold temperatures and a lack of weather today will allow our snowpack to further adjust, however it doesn’t take long to dig down to the ground to recognize the problematic weak layers that lie beneath our slow-to-build slab. Since the drizzle crust of December 7/8 (17 days ago) we have received 2.3 inches of water, which translates to about a 16-inch slab. Snow pit tests yesterday were consistently failing at this interface of faceted snow directly above the crust.

Small spells of moisture thus far have allowed our snowpack to adapt a little at a time, not overloading weak layers to the point of widespread natural avalanching yet. Add a skier or snowmachiner into the equation on steep, wind loaded terrain and producing an avalanche may be possible today. Specifically in the higher elevations where the wind has produced a deeper, heavier slab that overlies this same basic poor structure.

Avalanche Problem 2

Wind Slabs

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

Monday morning we did have a short lived, natural wind slab avalanche cycle where strong winds proved enough to overload weak layers. In higher elevation areas it’ll be possible to find pockets of dense wind slabs 1-2’ deep on the lee side of wind-raked ridges. Pay particular attention to firm, hollow sounding snow on south, east and west aspects. These slabs may sit mid-slope given the moderate to strong winds that blew through our region on Monday and Tuesday.

Weather

Wed, December 25th, 2013

Yesterday cloudy skies in the afternoon produced just a trace of new snow in eastern Turnagain Arm as a series of low-pressure systems skirted us to the south. Winds shifted to a more easterly direction but still blew moderately yesterday. Temperatures stayed cold at sea level due to a weak temperature inversion and gradually grew warmer with elevation topping out in the low-teens on Sunburst.

Don’t expect a Christmas miracle in the form of new snow today. Rather we seem to have fallen under another persistent high-pressure ridge that appears to be with us at least until the weekend. There is a decent temperature inversion in place this morning with temps ranging from 2 degrees in Portage to 20 degrees at the top of Sunburst. Winds appear to again shift back to a northwest orientation today blowing in the 10-20mph range.

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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