Sat, March 14, 2020 Turnagain Pass Avalanche Forecast

Sat, March 14th, 2020

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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.

Recent Avalanches

High volume human triggered sluffs were reported yesterday in areas at Turnagain Pass that were spared the wind damage from last week. These were on steep shaded slopes with very loose surface snow as well as steep southerly slopes in the heat of the day.

Avalanche Problem 1

Persistent Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Although valley bottom temperatures are chilly again this morning, they should heat up to the 30’s°F today with direct sunshine. Springtime! Along the ridgetops, temperatures are much warmer (in the 20’s°F this morning) and should increase several degrees. A light westerly breeze may keep the snow surface from heating up too much, but I’m guessing there will be slopes out of wind, in the sun, and feeling the heat.

As the days go by, we continue to assess a weak layer of snow that sits just 1-2 feet below the surface. This is composed of buried surface hoar and/or small facets. A lack of avalanche activity for the past several days, unremarkable pit results and observations from others all point to this layer becoming more stubborn to trigger. However, it can’t be written off, especially with warming temperatures and direct sun in the Alpine (this can do unexpected things in the spring).

Sun effect: Keep an eye out for the slopes that are warming and moistening the snow surface. Moist/wet sluffs are notorious for being ‘heavier’ and larger than expected and can easily knock someone off their feet and plow down to the valley bottom. As mentioned above, a warming slope can cause a weak layer to be more reactive and slab avalanche likelihood increases.

As folks travel to more remote areas, remember the snowpack could be quite different. Paying attention to signs of recent avalanches, cracking/whumpfing, wind effect, and sun effect are all key. Also, keep in mind areas with a shallow snowpack are more likely places to find a slab that fails in the weak layer described above or other old weak snow buried in the pack. This includes the south end of Turnagain Pass, such as Twin Peaks and Silvertip to Summit Lake and over toward Palmer Creek and the Raggedtop area near Girdwood.

We found this layer of buried surface hoar a foot deep at 3,000′ on Seattle Ridge. Although we could get it to fail, it did not want to propagate, which is a sign the layer is less likely to produce an avalanche.

Cornices: Avoid travel on cornices and move quickly underneath them. Remember, warming temperatures and direct sun are classic mechanisms for destabilizing these monsters.

Dry loose snow avalanches: In shaded areas that were protected from the wind, the snowpack is faceting significantly and dry sluffs are becoming larger.

A high degree of wind effect along Taylor Pass. 3.13.20. Photo: Billy Finley

Weather

Sat, March 14th, 2020

Yesterday: Sunny skies with some very thin high clouds at times. Ridgetop winds were light from the west (around 5mph). Temperatures warmed to the mid 20’s°F along ridgetops and 30°F at the lower elevations. Valley bottoms are back to the single digits this morning while ridetops remain in the 20°F.

Today: Another brilliant sunny day is on tap. Again ridgetop winds should be light, 5-10mph, from the west. Temperatures are forecast to be even warmer today as the high pressure spinning over us continues to bring in warm air aloft. Ridgetop temps may hit the upper 20’s°F and lower elevations the mid 30’s°F.

Tomorrow: Sunny skies, light west winds and temperatures nearing 30°F along the lower ridgetops are forecast for Sunday and Monday. A warm low-pressure front moves in on Tuesday, which will bring a chance for rain to 1,000′ and snow above. Precip amounts look to be small, in the .25″ for rain and just a few inches of snow in the higher terrain.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	21	68
Summit Lake (1400′)	16	30
Alyeska Mid (1700′)	19	78

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	W	7	14
Seattle Ridge (2400′)	22	var	2	7

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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