Sun, December 03, 2017 Turnagain Pass Avalanche Forecast

Sun, December 3rd, 2017

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

3 - Considerable

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

The first significant storm of the season is on the doorstep this morning, and it’s a warm one. Temperatures have begun to climb and winds are picking up from the East. A moisture laden band of snow is on the way from the Gulf and between 10 – 20″ of snow is expected today with another 10 – 20″ tonight above 1,000′. This is just what the snowpack needs – a big warm storm to hopefully stomp out the shallow, weak and precarious existing snowpack. Not only will this ‘rapid loading’ event be enough to create natural avalanches in itself, the loading will occur on a VERY weak snowpack making it that much easier for avalanches to release.

Again, travel in avalanche terrain during this storm is NOT recommended – in fact, today is a great day for Christmas shopping!

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During the past several days we have seen widespread human triggered avalanches due to our current snowpack structure. The set up is relatively simple, a slab averaging 12 – 20″ thick is sitting precariously on a layer of weak facets. Skiers have been able to trigger multiple avalanches from ridges and areas hundreds of feet away – this is how touchy we are talking. With a new load of snow on the way piling up on the existing slab, we can expect the balance to be tipped and widespread natural avalanches breaking near the ground.

Pre-storm snowpack structure from Sunburst at Turnagain Pass:

Tincan Common on Dec 1st – Skiers along looker’s right hand ridge, out of view, remotely triggered these three pockets while descending (Victoria Lytle photo)

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Weather

Sun, December 3rd, 2017

Yesterday, the mountains saw mostly overcast skies and light snow showers. Turnagain Pass picked up 1″ of snow in the past 24 hours and the upper elevations of Girdwood 2-4″. Winds during this time were 10-15mph gusting in the 30’s and temperatures in the mid 20’s F at treeline and the low 30’s at sea level.

Today, expect a potent storm day. Around 1+” of rain is expected to fall below 1,000′ and possibly 1,500′, this translates to 10 – 20″ of snow at the higher elevations. Tonight we could see another 1+” of rain and another 10 – 20″ of snow. Winds will be Easterly in the 30-50mph range with gusts to 80mph or more. Temperatures should climb to 30F on the 3,500′ ridgelines and 40F at sea level.

Monday, snowfall should taper off and temperatures cool slightly as the storm moves out. We may get a slight bit of visibility Monday afternoon before another front pushes in and a chance for additional snow on Tuesday. This week will be quite active weather wise. Stay tuned!

*Center Ridge SNOTEL is reporting erroneous temperature data. See Turnagain Pass DOT weather station for accurate temperature at 1000′.

**Seattle Ridge weather station anemometer is covered with rime is not operating at this time.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	*30	1	.1	16
Summit Lake (1400′)	29	1	.1	10
Alyeska Mid (1700′)	30	3	.48	19

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	NE	19	57
Seattle Ridge (2400′)	25	**n/a	**n/a	**n/a

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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