Tue, March 24, 2015 Turnagain Pass Avalanche Forecast

Tue, March 24th, 2015

Alpine

Above 2,500'

1 - Low

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

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

Today will be our last bout of sunshine before a multi-day storm cycle moves in tomorrow. Winds have already increased from the East on the ridgelines and are expected to be in the moderate (15-20mph) range through the day. There is very little snow available for transport considering a sun crust sits on the surface on all but Northerly aspects. However, with the complex flow patterns often seen, there could be areas where the loose settled snow from shady zones is blown into fresh wind slabs. Any new wind slab will likely be shallow, easy to identify, but also easy to trigger – especially if it sits on a slick crust.

Photo: The Easterly face of Lynx creek is covered with a shiny sun crust – hence, little to no snow available for transport with the Easterly winds in this area today. (Lynx is the drainage one looks at while driving South through Turnagain Pass).

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

It’s been just over a week since a layer of faceted snow was covered by a 2-3′ slab (post St. Patty’s Day storms 3/16 and 3/19) and widespread avalanche activity ensued. We have been talking about this problem extensively and the variable nature of where it exists and where it does not. In short, triggering a persistent slab is becoming more and more unlikely because 1) many slopes have either already avalanched, 2) the facets were blown away before the storm or 3) the slab/weak layer has adjusted.

That said: there is still a remote chance a person could trigger a slab up to 2′ thick that fails in weak faceted snow. Shaded aspects with no surface crust are the most suspect. Safe travel practices are encouraged – expose only one person at a time on a slope and have an escape route planned.

Additional Concern

Normal Caution

Normal Caution

Normal Caution means triggering an avalanche is unlikely but not impossible.

More info at Avalanche.org

Cornices:

Just because the winds will keep the sun from affecting the snow in many areas today, steering well clear of cornices is always a good idea. Cornice crevasses are also likely to be found; this is where the cornice pulls away from the ridge underneath and creates a crack.

Wet Avalanches:

Slopes with a Southerly tilt that are sheltered from today’s winds may warm enough to soften sun crusts and allow for human triggered wet loose avalanches. As is the norm, if you find yourself in boot-top, wet and unsupportable snow, it’s time to move to a different aspect.

South facing slopes have seen the full effects of the sun recently! Photo: Breakable crust on Corn Biscuit

Weather

Tue, March 24th, 2015

Yesterday was one of those brilliant blue-bird days in Alaska. Temperatures were warm, in the 30’s F, and winds were calm with an occasional light breeze on the ridgetops from the East.

We have one more sunny day on tap before stormy weather tomorrow. Ridgetops winds have just started to kick up from the East this morning and will remain in the 15-20mph range. Temperatures should stay warm at the parking lots, ~35F, yet stay cooler on the ridgelines, ~25F.

Looking forward to Wednesday and later in the week, a series of shortwaves (imbedded disturbances) will spin around a large low-pressure South of Kodiak bringing a several day storm cycle to Southcentral. This pattern looks to remain – more or less – through Sunday. The storms will be warm, but at this point not terribly warm with a rain/snow line hovering around 1,500′. Accumulations for the first pulse of moisture (Wednesday through Thursday) are looking to be in the 1″ H20 range; this equates to around a foot of snow up high. Stay tuned!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	36	0	0	55
Summit Lake (1400′)	29	0	0	12
Alyeska Mid (1700′)	35	0	0	32

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	NE	4	21
Seattle Ridge (2400′)	28	n/a	8	27

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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