Mon, December 04, 2017 Turnagain Pass Avalanche Forecast

Mon, December 4th, 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

As of this morning, the potent storm over us is slowly degrading and exiting. The good news is, winds (that were off the chart yesterday) have decreased overnight and snow is still falling. The rain/snow line is just above 1,000′ currently and forecast to lower to around 800′ with slightly cooling temperatures. We should see an additional 4-8″ through the day at the higher elevations with another 3-4″ tonight. Curious of the snow totals so far?

Estimated Storm Totals (beginning 6am yesterday till 6am today):

Girdwood Valley: ~2″ rain lower elevations, 2-3+’ snow high elevations
Turnagain Pass: 1.8″ rain lower elevations, 2-3+’ snow high elevations
Summit Lake: .3″ rain lower elevations, 3-8″ snow high elevations

Recent avalanche activity? There is much uncertainty as to the extent of the natural avalanche cycle yesterday and overnight. As is the case during these stormy conditions, low visibility and darkness hamper visual observations. Nonetheless, we can expect that the mountains are still undergoing significant changes. Upper elevations have seen 2-3+’ of feet of snow in less than 24 hours – and it’s still snowing and blowing… This is a simple rapid loading event and a text book case for how-to-make-avalanches. Hence, steering clear of avalanche terrain (slopes over 30 deg) with nothing above you (avoiding runout zones) is essential.

If we dig a bit deeper into what the mountains are going through and a look to the future, many slopes could be sliding, or will soon, and fill back in. This is what we’d like to see because it helps to clean out the weak layers from November. However, there are those slopes that will hang in the balance and allow the snow to pile up. These are the most likely ones that can get us in trouble when the storm passes. They will still have the weak snow under the new snow, which makes them more susceptible to human triggers, and they will also produce larger avalanches. Telling the difference from slopes that have slid and ones that haven’t can be difficult to impossible. Also, just because a slope slid doesn’t mean it won’t again, especially the first couple days after this cycle. Keep these thoughts in the back of your head as you look forward to enjoying the new snow.

Weather

Mon, December 4th, 2017

Yesterday’s warm storm began around 9 am and as of 6am this morning ~1.5 – 2″ of rain has fallen below 1,000′ and 2-3+’ of snow above. The rain/snow line crept up last night and is hovering just above 1,000′. Winds were some of the strongest we have seen for a while from the East, averaging 40-70mph with gusts over 100. Winds have backed off to the 20-30mph range for averages this morning, remaining from the East. Temperatures have been near 38F at sea level and the upper 20’s on the higher ridgelines.

Today, we should see the rain/snow line lower to 800′, possibly further, with .4-.5″ of rain below and 4-8″ of snow above. Tonight cooler air should continue to drop the rain/snow line and an additional 3-4″ is possible at sea level with 4-6″ at the higher elevations. Winds are forecast to shift Southerly and decrease somewhat to 15-30mph. Temperatures are expected to hover near 38F at sea level and the upper 20’s on the 3,500′ ridgelines.

Tuesday, the slightly cooler air is expected to stay in place as this system continues its slow exit. We could see continued snowfall with a rain/snow mix at sea level. Looking toward to later this week, warmer air and precipitation looks to filter back our way. Stay tuned.

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

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	*31	15	1.8	31
Summit Lake (1400′)	34	0	0.3	9
Alyeska Mid (1700′)	33	2	1.7	20

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	24	ENE	59	124!!
Seattle Ridge (2400′)	28	SE	25	61

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
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

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