Thu, March 07, 2013 Turnagain Pass Avalanche Forecast

Thu, March 7th, 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

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

Fresh wind slabs will be the primary concern today as this storm is expected to move into our area with 55 to 75 mph southeast winds at ridgetop elevations. Winds began to pick up around 4am and by 6am are gusting into the mid 50’s at 3800’. Above about 1200’ we found generally loose, dry snow yesterday that is available for transport by the wind. As winds blow the surface snow around, expect slabs to form on north and west aspects, particularly below ridges. Falling snow at mid and upper elevations will further add to building wind slabs as this storm intensifies through this afternoon and evening.

Cornices will continue to build and fail throughout this storm event. As always, limit your time spent underneath cornices and if travelling on a corniced ridge, when you think you are far enough back from the edge, it’s good practice to move back even further!

Avalanche Problem 2

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

Depending on the timing of this storm, precipitation could add up to significant amounts by this afternoon/ evening where storm snow avalanches could be an issue. Yesterday Fitz and I found a couple of concerns on the surface in the form of a sun crust on southerly aspects at and above tree line (formed Tuesday) and very sporadic and pocketed surface hoar. Whether or not the surface hoar stays in tact, I suspect these mid-elevation southerly aspects could be some of the first avalanche producers as storm snow accumulates and forms a slab. If the bulk of precipitation does not come until later in the day or this evening as forecasted, storm snow avalanches will prove more of a concern on Friday.

Weather

Thu, March 7th, 2013

Temperatures were mild and winds were calm as high clouds dominated our region yesterday in anticipation of our first real shot of moisture in seven days.

Today looks to be a bit more exciting in the weather department as a 956mb low southwest of Kodiak begins to impact our area. Winds have already begun their influence and will continue to blow from the southeast in the 55-75mph range today at upper elevations. The temperature will gradually increase throughout the day with rain being the predominant precipitation type at sea level by this afternoon. The snow line looks to be around 700ft today in the eastern Turnagain Arm area. This storm will start off windy with the bulk of precip coming later this afternoon and overnight.

We will likely continue to feel the effects of this storm tomorrow as it makes landfall and subsequently weakens. For the weekend, cloudy with a chance of precipitation looks to be the story as a series of weak lows progress across our region.

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Fitz will issue the next advisory on Friday, March 8th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/27/23	Turnagain	Avalanche: Tincan Ridge	Schauer/ Stiassny Forecaster
11/26/23	Turnagain	Observation: Road report: Slide with dirt on Repeat offender	Anonymous
11/26/23	Turnagain	Observation: Pete’s North	Ben Sullender
11/25/23	Turnagain	Observation: Tincan trees	John Sykes Forecaster
11/21/23		Observation: Spokane Creek	John Sykes Forecaster
11/20/23	Turnagain	Observation: Sunburst	Anonymous
11/19/23	Turnagain	Observation: Magnum – PMS Bowl	Schauer/ Cullen/ Jonas Forecaster
11/19/23	Other Regions	Observation: Sunnyside/Penguin	Jose Ramos-Leon
11/19/23	Turnagain	Observation: Eddies	Andy Moderow
11/19/23	Turnagain	Observation: Cornbiscuit	Anonymous

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