Tue, March 12, 2024 Turnagain Pass Avalanche Forecast

Tue, March 12th, 2024

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

Wed, March 13th, 2024

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

Wed, March 13th, 2024

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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.

Recent Avalanches

Visibility yesterday was very poor, but we did hear of one human triggered storm slab yesterday evening near the motorized uptrack on Seattle Ridge.

Avalanche Problem 1

Storm Slabs
N E S W NW NE SE SW

Aspect/Elevation
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.

Aspect/Elevation of the Avalanche Problem

Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

With 1′-2′ of new snow on the ground throughout the Turnagain forecast zone, easterly winds blowing 20 to 30 mph, and another 8″-2′ of new snow expected today with increasing temperatures, natural avalanches are expected and human triggered are very likely at all elevations and all aspects. Travel in avalanche terrain today is not recommended. Both storm and wind slabs will be the primary concern and these avalanches could be 2-3′ deep by the end of the day today. Because of the weak layers that existed on the surface prior to this storm it’s possible these avalanches could be larger than expected and more sensitive to trigger. More on this in the additional concern. Today is a day to be looking out for what is above you. If you are getting out to storm ride today we recommend sticking to slopes less than 30 degrees and being sure to stay out of the runout of any slide paths.

Forecasted snowfall totals from 4pm Monday to 4pm Tuesday, March 12. Image courtesy of the NWS Anchorage. 3.11.2024

Visibility yesterday, March 11 in Lynx Creek. We expect similar visibility today as the storm continues. 3.11.2024

Additional Concern

Persistent Slabs

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.

More info at Avalanche.org

There are a few weak layers we are tracking that could cause the storm slabs we are expecting today to be larger and easy to trigger. There is a layer of facets that was buried on March 5 that caused some wide-propagating avalanches. Additionally, surface hoar was observed on the surface on March 9 in the Sunburst area at all elevations. Some of this surface hoar was sitting on a sun crust, which can make it especially reactive once it becomes buried. Surface hoar has a nasty habit of being sensitive to trigger remotely and at lower slope angles than most avalanches. We will be watching to see if either of these layers becomes reactive with this new load of wind and snow.

Weather

Tue, March 12th, 2024

Yesterday: The storm that began Sunday night was the first in a series of low-pressure systems moving through south central Alaska today and tomorrow. Yesterday’s storm brought about 1″ of water to Turnagain Pass (18″ new snow) and Girdwood (14″ new snow) and a bit more in the Placer Valley. Temperatures were in the mid-20’s bringing cold snow to sea level throughout the day. Ridgetop northeasterly winds picked up into the teens mph in the morning gusting to 30 and as of last night are blowing steadily in the 20 to 30 mph range gusting in the 40’s.

Today: The storm continues today with another 8-12″ new snow forecast for Turnagain Pass by the end of the day. Girdwood looks to be on the lighter end of snowfall today with 4-6″ expected. Placer Valley again is favored expecting 1-2′ today. Unfortunately, it looks like temperatures are going to rise to just below freezing at Turnagain Pass and rain line may creep up to 700′ today in places like Girdwood and Seward. Ridgetop winds are expected to remain elevated today in the 25 to 30 mph range out of the east gusting into the 40’s mph.

Tomorrow: Tomorrow the precipitation is forecast to taper off with light showers continuing throughout the day totaling a few inches of new snow. Temperatures should cool slightly bringing snow back to sea level before the storm moves out. Ridgetop winds look to remain in the 25 to 30 mph range tomorrow with higher gusts.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	24	18	1.5	111
Summit Lake (1400′)	21	3	0.3	48
Alyeska Mid (1700′)	23	14	1.3	98
Bear Valley – Portage (132′)	23	20	1.6	–
Grouse Ck (700′)	24	10	1.0	75

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	17	ENE	15	48
Seattle Ridge (2400′)	20	ENE	5	14

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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