Thu, December 10, 2015 Turnagain Pass Avalanche Forecast

Thu, December 10th, 2015

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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

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

The GOOD NEWS: A quick hitting snow event rolled through last night and has, so far, added 10″ of new snow at Turnagain Pass. Girdwood Valley has seen slightly less with 8″ overnight and Summit Lake much less, only 2-3″. When adding last night’s total to yesterday’s 2-4″, we have a 24-hour accumulation of 10-14″. This is “low density” new snow which is great news, but that leads us to the 2nd part of the story…

The BAD NEWS: This new snow has fallen on a VERY weak surface with a hard bed surface below (see photo). Although it’s only a foot of new snow, it will simply have a hard time sticking to the old sugary snow below. Adding to this, avalanches triggered could run far with the help of the hard bed surface underneath. In short, this is classic case for creating very touchy avalanche conditions. This means you are more likely than not to trigger an avalanche if you enter slopes over 35 degrees. The exception are slopes where the new snow is so unconsolidated that it is not forming a slab – in this case, large sluffs can be expected.

Things to watch for if you are headed out:

Stiff, harder snow over weak, softer snow
– Hand pits are good ways to assess how the storm snow is bonding to the older ‘faceted’ weak snow
Shooting cracks in the new snow
Whumphing, or collapsing of the new snow into the weaker snow below

Photo below is from yesterday of the ‘weak’ faceted snow that sits on top of a hard bed surface. Imagine a cohesive slab of snow 12″ thick sitting on top of this weak layer/bed surface combination – yep, that’s what we have this morning and it’s a problem…

Weather

Thu, December 10th, 2015

Yesterday’s light snowfall added 2-3″ before intensity increased overnight adding another 10″ at mid elevations. (Check out the Turnagain Pass Snow Stake by clicking this link!). Winds have been Easterly and moderate with Sunburst averaging in the 20’s mph overnight and Seattle in the teens. Temperatures have decreases slightly with the snowfall as well and are sitting in the mid-20’s F this morning on ridgetops.

Today we can expect snowfall to decrease and skies start to break. Winds should remain from the East in the 15-20mph range and temperatures in the mid 20’s F at the mid and upper elevations.

Looking to Friday night and weekend, a potent storm system is slated to arrive that could bring “incredible snow rates” to Turnagain Arm and Anchorage – see this NWS discussion HERE.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	10	1	34
Summit Lake (1400′)	29	2	0.2	13
Alyeska Mid (1700′)	30	8	0.8	23

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	26	NE	16	44
Seattle Ridge (2400′)	27	SE	10	22

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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