Mon, February 16, 2015 Turnagain Pass Avalanche Forecast

Mon, February 16th, 2015

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

3 - Considerable

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

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

New snow and wind have combined to create very unstable slabs in the 8-12” range. Ridgetop winds have picked up into the 40 mph range out of the East/Southeast overnight and will remain strong through the day. An additional 10-12” of snow and, more importantly, 1” of H20 forecasted for the higher elevations will increase the size of these slabs into the 2 foot range. These slabs will release naturally in some locations and will be very sensitive to human triggers. Rapid loading that occurred overnight and will continue throughout the day is enough of a trigger to initiate avalanches.

This is not a complicated situation. Avoidance of avalanche terrain is the only way to “manage” this problem today.

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

A layer of weak snow that sits anywhere from 8” to 3 feet below the surface is the most concerning layer today. Avalanches occurring in the upper layers have the potential to step down to this layer. In cases where this happens, the volume will be large and potential for burial, if caught, is high. Avalanches occurring at this layer have a high propagation potential, which means that fractures can and will travel across slopes and over long distances.

Because of this travel in avalanche terrain is not recommended today (have I mentioned that already?). While this problem exists mainly in the Alpine elevations, it will be important to avoid the runout of terrain from above when traveling in the Treeline elevations.

Additional Concern

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

Rain falling on snow as high as 2,000’ will weaken the surface snow. This will result mainly in wet loose avalanches. Volume will be generally low, as the snow in the mid and lower elevations has already been hit with periods of rain over the past few days and has had time to adjust. With that being said, it will be important to avoid steep terrain where the surface snow is wet. If you find yourself sinking through the snow deeper than your boot it is time to move to lower angled terrain. Consequences of wet loose surface snow moving will become high if pushed into or over terrain traps such as cliffs, gullies, glide cracks, or trees.

Weather

Mon, February 16th, 2015

Yesterday brought a continuation of warm, wet and windy weather to the area. Temperatures were in the mid 20s F along ridgetops. Temps at sea level climbed into the high 30s – low 40s F. A mix of rain and snow have been falling with the Center Ridge SNOTEL site picking up 5 € of snow containing .5 € of H20. The rain/snow line fluctuated and was around the 1,800′ mark for most of the 24 hour period. Winds cranked back up with Sunburst averaging in the 30 mph range with a max gust of 96 mph.

A strong surface low currently parked just south of the Alaska Peninsula is pulling a warm stream of moisture from the South over the area. Today will bring intense periods of precipitation and high winds, with an additional 10-12 € of snow and 1 € of H20 above the rain/snow line. The rain/snow line should be around the 1,600′ mark. Winds will be strong out of the East at 40-50 mph. Temperatures will remain warm with ridgetops approaching 30 degrees F.

Wind and precipitation intensity should begin to taper off by tonight. Temperatures will cool slightly and a chance for showery precip will remain through the middle of the week.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	5	.5	39
Summit Lake (1400′)	36	rain	.1	9
Alyeska Mid (1700′)	33	2/rain	.4	27

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	E	31	95
Seattle Ridge (2400′)	27	SSE	27	63

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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