Sat, March 16, 2019 Turnagain Pass Avalanche Forecast

Sat, March 16th, 2019

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. 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
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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

Each low-pressure event impacting our area over the past week seems to be bringing slightly warmer temperatures than the last; today will be no exception. As temperatures increase, the rain/ snow line may reach as high as 2,000’ as this next bout of weather impacts the eastern Kenai Peninsula this weekend. What does this mean for avalanche activity today? It means that rain on snow may initiate natural avalanches in the treeline elevations where we’ve seen mostly snow for the past 3+ days. Any avalanches today will be large and un-survivable as storm slabs alone are 2-3’ deep. Add winds to that or the potential for an avalanche to step down into weaker layers deeper in the snowpack and we’re flirting with the potential for 5-6’+ deep avalanches.

Though observations and info from the alpine (above) 2,500’ have been minimal since Tuesday, an additional 8-16″ of snow forecated and strong easterly winds over known weak layers and crusts create a serious concern for large and destructive avalanches today. In channeled terrain, debris was running to the valley floor and all the way to sea level in some cases yesterday. Today the message is simple – Avoid all avalanche terrain, this includes slopes steeper than 30 degrees and all runout zones.

South of Turnagain Pass: A brief weather window on Thursday allowed observers to view a plethora of natural avalanches that ran mid-storm. Given a shallower snowpack in these areas, this week’s load is proving generous enough to tip the stress vs. strength balance south of the core Turnagain Pass area. Suspect areas include Johnson Pass, Lynx Creek and Summit Lake.

Debris in channelled terrain in the bottom of east facing terrain at the base of Twin Peaks. Just south of Turnagain Pass. Photo: 3/14.

Storm Totals (Wed 6am – Sat 6am):

Turnagain Pass 1800’: 29” (settled snow) — 4.3” SWE
Girdwood-Alyeska Midway 1700’: ~30” — 3.14” SWE
Summit Lake 1400’: ~19” — 1.5” SWE
Portage Valley 95’: ~5-6 ft snow in upper elevations — 6.25” rain at reporting station

Weather

Sat, March 16th, 2019

Yesterday: Temperatures in the mid to upper 30’s kept rain the dominant precip type below about ~700′. Turnagain Pass (1,880′) only saw ~3 € of wet, heavy snow (.9 € water) as accumulation was barely keeping up with settlement rates. Ridgetop winds were sustained from the east in the mid 30’s €“ 40mph with gusts into the low 70’s at Sunburst.

Today: Temperatures continue to climb into the high 30’s at 1,000′ with the rain/ snow line anticipated to be in the 1,800′ €“ 2,000′ range. On average we can expect another ~1 € of water though areas such as Portage and Girdwood could see more. In the alpine this translates to another 8-16 € of snow.

Tomorrow: The active weather pattern continues as yet another surface low moves into southcentral AK. Expect more rain in the lower elevations, moderate to strong southeasterly winds and ample snow/ whiteout in the alpine. Rain/ snow line looks to be in the 1,800-2,400′ range.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	32	3	.9	102
Summit Lake (1400′)	35	0	.2	37
Alyeska Mid (1700′)	32	0	.89	89

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	23	ENE	42	88
Seattle Ridge (2400′)	28	n/a *	n/a*	n/a*

*Seattle Ridge weather station is not reporting reliable wind data at this time.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg

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