Thu, April 06, 2017 Turnagain Pass Avalanche Forecast

Thu, April 6th, 2017

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

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

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

For the past week, observations have been limited due to elevated avalanche danger and poor visibility. A brief window into the alpine yesterday confirmed our suspicions that we are still within a very active natural wet avalanche cycle. Temperatures were the warmest we’ve seen all spring at ridge top locations yesterday and the mountains surrounding Turnagain Pass appear to be going thru a spring ‘shed-cycle’ of sorts. Large natural avalanches are failing on all aspects, particularly in the mid-elevation band below about 2,500’ and showing potential to propagate across wide distances. What hasn’t avalanched yet will be stressed by another half inch of water weight today. These could fail either as storm slabs (2-4’ deep) or step down into weaker snow near the ground (4-6+’ deep). At this point it doesn’t really matter what the weak layer because this is not an avalanche problem to mess with or try and out-smart. The snowpack will remain touchy and with natural avalanches likely again today, travel in avalanche terrain is not recommended. Avoidance will be your best and only tactic until this warm and wet pattern of storms subsides and we can take stock of what is left of our snowpack.

Nearly wall to wall avalanching on Seattle ridge (lookers left of the common snowmachine up-track) “Repeat offender” path as viewed from the Seward Highway.

WIND SLABS and CORNICES:

Strong winds last night combined with more snow will act to create large wind slabs and cornices on leeward slopes in the upper elevations. With temperatures rising to above freezing in the alpine these may release naturally and could entrain enough snow to run quite far. Any additional wind and precipitation today will add further stress.

How much load is on the old weak surface from March? Storm totals (March 27 – 6am April 6th):

Turnagain Pass: 4.7″ of H2O, 48+” of snow at upper elevations
Girdwood Valley: 5.5″ of H2O, 55+” of snow at upper elevations
Summit Lake: 1.6″ of H2O, 15+” of snow at upper elevations

Widespread avalanching on Eddie’s lower rolls as seen from the RWIS web cam during a brief period of clearing yesterday afternoon.

Avalanche Problem 2

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

The balance has been tipped and avalanches this week have been observed stepping down into old weak layers. Dirty debris in places is indicative that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6′ and running the entire length of a slide path. Again, avoidance is key with this problem as a persistent slab avalanche in our current snowpack is not a survivable event.

Recent full-depth avalanche on Seattle ridge (across from Sunburst) stripping out the entirety of our snowpack.

Weather

Thu, April 6th, 2017

Daylight hours yesterday provided a brief reprieve from the deluge of wet, cloudy weather (enough to view the alpine) though we still ended the 24-hour period with .5 – .7 € of water and likely another 5 €“ 10 € of snow above the freezing line (~2,000′). Temperatures were WARM with the Center ridge SNOTEL topping out at 44 degrees (1,880′) and Sunburst weather station (3,800′) reaching a high of 30 degrees. Overnight, another front impacted our area with temperatures dipping slightly and east winds increasing quite dramatically around 6pm with Sunburst measuring a 7-hour period of sustained winds in the 40’s and gusting into the 70’s mph from the east.

You guessed it, another storm day on tap for our region today! Temps should cool slightly (mid-30’s at 1,000′) from yesterday bringing the rain/ snow line back down somewhere closer to 1,500′. Expect another .5 € of water and winds again from the east in the 20 €“ 45mph range at ridge top level.

Looking out toward the weekend we may see a break in this overall pattern and see some clearing with slightly cooler temperatures by Saturday and Sunday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	40	0	.7	79
Summit Lake (1400′)	38	0	.1	27
Alyeska Mid (1700′)	35	0	.5	72

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	E	26	74
Seattle Ridge (2400′)	30	E	32*	75*

*Winds reporting since 3pm

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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