Tue, March 01, 2016 Turnagain Pass Avalanche Forecast

Tue, March 1st, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

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

With just a few short breaks in weather over the last 9 days, we appear to be on the verge of a pattern change as it looks like we’ll be under at least a couple of days of high pressure starting this afternoon. Storm snow issues listed below are of concern today and may prove more reactive if we get a spike in ambient temperatures, or a period of unobstructed sunshine.

Storm slabs: Yesterday we found reactive storm slabs at 2500’ in our snow pit that consistently failed and propagated about 2 feet below the surface. Granted, this is only one data point, but it happens to be on arguably the most heavily traveled piece of terrain in the Turnagain zone (Seattle ridge uptrack). This may have been the same weak layer responsible for a Sunday afternoon natural storm slab on Tincan. More data will help us understand if this weakness is widespread, but for today, keeping slope angles mellow and picking very conservative travel routes will be key.

Pit results yesterday identified a concerning mid-storm crust at 2500′ on Seattle ridge that proved reactive. See video here.

Wind slabs: There is ample snow available in the alpine for transport. Winds have been primarily from the E and NE over the last several days loading any slope with a westerly tilt. Last night, winds kicked back up into the 40’s, gusting to 70mph on Sunburst. As with their cornice brethren, wind slabs have the potential to be large and dangerous today. Avoid steep, wind loaded slopes and recognize that any direct sun today could act to weaken these wind slabs.

Cornices: These continue to grow large and unruly with the addition of more wind and snow. Give cornices a wide berth if travelling on or below a corniced ridge. Any significant cornice fall today is likely to trigger an avalanche on the slope below.

Avalanche Problem 2

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

The wild card…. Glide cracks have continued to release during this storm cycle, still with no real discernable pattern. Many cracks continue to litter the slopes above well-travelled terrain on both the motorized and non-motorized side of the highway. Simply avoid exposure time spent below existing cracks to minimize your risk. The photo below is a good reminder that if a skier or snowmachiner were to tangle with one of these full-depth glide avalanches, odds of survival are slim to none.

Snowmachine for scale next to the toe of a glide avalanche. This released Thursday night/ Friday morning on the East face of Seattle ridge depositing 15-20′ of debris on a well-traveled snowmachine route.

Weather

Tue, March 1st, 2016

Temperatures at 1,000′ were slightly cooler yesterday (32F) than they have been for several days. This promoted a discernable rain/ snow line at about 500′ with a few short bursts of snow at sea level before turning to all rain. New snow accumulation added up to 4-6 € at 1,000′. Winds were in the teens and gusting to the 30’s mph at ridgetop locations as clouds funneled in and out of the Pass.

A pattern change is underway today as stormy weather gives way to clearing skies, calming winds and cooler temperatures overnight tonight. Today winds are expected to start out in the 15-30mph range from the East, dropping off to single digits by this afternoon. Temperatures at 1,000′ will be in the low to mid-30’s F before cooling off overnight and we may see 1-2 € of snow squeezed out this morning before skies break apart.

High pressure will dominate through Thursday before our next chance of snow arrives prior to the weekend.

A quick snapshot of SWE data at the Turnagain Pass SNOTEL thru February. Red is current water year. Green is the long-term average and blue is the year we’d all like to forget (last year).

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	30	4-6″	.6	146
Summit Lake (1400′)	32	0	.1	41
Alyeska Mid (1700′)	32	2	.2	106

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	ENE	26	70
Seattle Ridge (2400′)	24	n/a	n/a	n/a

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster

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