Tue, February 14, 2017 Turnagain Pass Avalanche Forecast

Tue, February 14th, 2017

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

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. Dangerous avalanche conditions.	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

Numerous natural avalanches were observed yesterday and natural activity is expected throughout the day with continued weather impacting our region. This includes large natural slab avalanches 2-5’ thick in the alpine and wet avalanches below 2000’ due to heavy rain and above freezing temperatures. Avalanche activity could run the full length of a slope, thus it will be important to stay off any slopes greater than 30 degrees and avoid being near any runout zones today. This set up could be a hazard even in the Tincan Trees where a small terrain features could have high consequences. In channeled terrain an avalanche from above could easily entrain wet snow in the lower elevations and run further than expected. This will be especially important in places like Portage Valley, Johnson Pass trail and the flats below Seattle Ridge.

Storm totals for Turnagain Pass over the last two days are estimated around 2-3’ in the alpine with an additional 10-12” possible today. For the second evening in a row ridgetop winds from the East (SE to NE) have picked up into the 40s and 50s mph and early this morning several gusts reached over 100 mph at Sunburst weather station. Above freezing temperatures have been recorded at Center Ridge weather station (1800’) and its possible that rain/snow line may reach 2000’ by this afternoon.

In the afternoon temperatures are expected to increase as precipitation and winds back off. Similar to yesterday natural activity may increase with a little afternoon sun and/or above freezing temps in the upper elevations. Again it will be important to avoid ALL steep terrain and maintain a conservative distance from all run-out zones.

Avoidance of avalanche terrain is the only way to “manage” this problem today.

A natural avalanche observed in Portage Valley yesterday afternoon near Williwaw Campground. This avalanche was well away from the road cooridor.

Partial clearing in the afternoon allowed the DOT web cam to catch this avalanche some time after it released on Tincan, CFR ridge. It was first noticed at 2:35pm on the web cam, but this is the best photo.

Wet loose activity was observed on many slopes after the sun appeared briefly in the afternoon. Photo taken near Portage turn.

Avalanche Problem 2

Deep Persistent Slabs

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

More info at Avalanche.org

Weak snow (facets and depth hoar) in the lower layers of the snowpack continues to be a concern in our advisory area. Today avalanches occurring in the upper layers have the potential to step down and release the entire snowpack in some places. If this does happen the volume will be large and could run long distances.

Travel in avalanche terrain is not recommended today including being in the runout of a steep slope.

Weather

Tue, February 14th, 2017

Yesterday above freezing temperatures were observed along Turnagain Pass with a partial clearing late afternoon, where the sun was observed briefly. Strong (40-50mph) Easterly ridge top winds decreased to moderate (20-30mph) in the afternoon. Overnight ridge top wind increased into the 40-60’s mph range with several gusts in the 90-100mph mph’s on Sunburst weather station. In the last 24 hour (6am to 6am) about 12-15 € of snow fell in upper elevations (1 € of H2O) in Turngain Pass and 15-20 € of snow (1.5 € H20) in Girdwood.

Today as an intense front moves through our region heavy precipitation is expected to last through mid morning, this is snow above 2000′, with an additional 10-12 € of snow. Strong Easterly ridgetop winds are expected to decrease into the 20-30mph range by early afternoon, but expect gusts to still be in the 40’s mph. Expect above freezing temperatures into mid elevations and rain/snow line to be as high as 2000′.

Tonight temperatures are expected to cool and winds will deminish. Cooler temperatures are expected into this week and more precipitation will hopefully bring snow instead of rain to lower elevations throughout the week.

*Seattle Weather station was not working for part of the day yesterday and there appears to be an issue with the temperatures sensor.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	36	11	1.0	74
Summit Lake (1400′)	34	1	.3	27
Alyeska Mid (1700′)	33	5	1.45	62

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	ENE	39	107
Seattle Ridge (2400′)	*n/a	*SE	*20	*51

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/16/23	Turnagain	Observation: Tincan Common	William Finley
11/14/23	Turnagain	Observation: Sunburst/Magnum	Adrian Beebee
11/14/23	Turnagain	Observation: Seattle Ridge	Schauer/ Creighton/ Ellis Forecaster
11/13/23	Turnagain	Avalanche: Tincan Trees	Eeva Latosuo
11/12/23	Turnagain	Observation: Sunburst	Schauer/ Creighton/ Nave Forecaster
11/12/23	Turnagain	Avalanche: Goldpan – avalanche	Mike Records
11/11/23	Turnagain	Observation: Tincan Common	Andy Moderow
11/11/23	Turnagain	Observation: Taylor Pass – Sunburst	Wadsworth / Stwertka
11/10/23	Turnagain	Observation: Tincan	Andrew Schauer Forecaster
11/10/23	Turnagain	Observation: Tincan Trees	Michael Kerst

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