Thu, December 04, 2014 Turnagain Pass Avalanche Forecast

Thu, December 4th, 2014

Alpine

Above 2,500'

2 - Moderate

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

There is uncertainty as to how much new snow the Eastern Turnagain Arm will see today. Likely, some areas will get several inches while a couple ridgelines over may see only a trace. In areas seeing several inches or more of new snow, fresh wind slab avalanches will be the main concern. The winds are forecast to average between 15-25mph, which are ideal wind loading speeds. The Seattle Ridge weather station is reading in this range this morning while the Sunburst weather station is quieter (~10mph) with speeds increasing through the day.

The good news is, the warm temperatures (mid 20’s F) above treeline will help to stabilize the new snow relatively quickly. Your best bet at triggering an avalanche is to step on a very fresh wind loaded slope. Watch for wind loading in action and areas where the snow is more cohesive and cracking around you. These slabs should be in the 5-10″ range and fairly soft.

Below is a look at yesterday’s surface. This area, in the Summit Lake region, is quite wind affected, however many areas still harbor soft settled powder.

Avalanche Problem 2

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

Dry snow sluffs at the upper elevations are possible while wet, or moist, snow sluffs are possible near treeline. Temperatures look to climb to 32F near treeline, which will moisten any new snow that falls. These should be low volume and something to keep in mind on steep slopes over 40 degrees.

Weather

Thu, December 4th, 2014

Weather yesterday was mostly cloudy with light to moderate Easterly winds. A trace of snow was picked up at Turnagain Pass with the rain/snow line near sea level. Overnight, temperatures have warmed a few degrees to the mid 20’sF on the ridgetops and 30F at treeline. This is associated with a large scale Southeasterly flow that is pumping warm air our way from the South.

Today, we are expecting a pulse of moisture embedded in the Southerly flow to add 3-5″ of new snow with slightly warming temperatures (up to 32F at treeline and the upper 20’sF on the ridgetops). Rain (and maybe a rain/snow mix) is expected at sea level. Winds should remain 15-25mph from the East.

This general pattern is expected to continue into the weekend with off-and-on snow showers above 1,000′ and rain below – amounts of snow are uncertain but look to be only a few inches here and there. We could see a break in cloud cover and precipitation tomorrow, Friday.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	1	0.1	19
Summit Lake (1400′)	24	0	0	5
Alyeska Mid (1700′)	29	1	0.1	17

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	E	10	30
Seattle Ridge (2400′)	24	NE	15	26

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster

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