Sun, March 17, 2019 Turnagain Pass Avalanche Forecast

Sun, March 17th, 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

Temperatures are rising as yet another storm moves into the region. As of this morning, rain is falling up to 1,500′ with wet snow above this. The rain line is expected to rise as high as 2,500′ in places and drop around an inch of water over the day. The higher elevations are expected to see up to a foot of new snow. This will give the mountains another shock to the system as rain-on-snow could induce natural wet avalanches on steep slopes below 2,500′. Snowfall and strong winds at the upper elevations will continue to load slopes and natural dry snow avalanches are expected. As storm after storm keeps adding more snow to these high elevations, the avalanches are becoming larger, sending debris further and nothing to mess with. There is anywhere from 5-8+ feet of settled storm snow from over the past week and with more snow on the way, it is another day to leave the mountains to themselves.

With obscured skies limiting visibility, it’s difficult to gauge the extent of naturally occurring avalanches over the past week. However, all it takes is a look at the bottom of avalanche paths and you’ll find most are filled with debris. Check out the video below, courtesy of Dwayne Clevenger, that shows debris covering the trail into Lynx Creek drainage. The message here is, avalanche terrain is not only on slopes over 30 degrees, it also includes runout zones (flat areas under steep slopes). Other trails, such as Byron Glacier trail or Johnson Pass trail, run through avalanche terrain and are examples of areas to be avoided during stormy weather.

Big thanks to Dwayne Clevenger for this video of avalanche debris covering the Lynx Ck trail on Mar 16, link HERE.

5′ settled storm snow video link HERE.

Around 5 feet of snow has piled up since March 8th. The snowpack has almost doubled since then, yet is settling fast with the rain and warm temperatures.

Storm Totals (Wed 6am – Sun 6am):

Turnagain Pass 1800′: 25″ — 4.9″ SWE (As seen above, 5′ of settled storm snow was found at 2,100′)
Girdwood-Alyeska Midway 1700′: ~30″ — 4.3″ SWE
Summit Lake 1400′: ~16″ — 1.6″ SWE
Portage Valley 95′: ~6-8+ ft snow in upper elevations — 9.25″ rain

Weather

Sun, March 17th, 2019

Yesterday: Another warm stormy day was over the area. Skies were mostly obscured with light rain falling below 800 – 1,100′ and moist snow above this. Roughly 1″ of rain fell in Girdwood while just over 1/2″ of rain fell on Turnagain Pass; Portage Valley was the winner with 3″ of rain. Snow amounts can be equated to 12-18″ at the higher elevations in Girdwood and 5-8″ at the higher elevations on Turnagain. Ridgetop winds have been easterly in the 30-40mph range with gusts up to 70mph. Temperatures reached the mid 30’s F at 1,000′ and the upper 20’s F along the ridgelines.

Today: Another wave of precipitation and wind is hitting us today. This storm front is warmer and 1″ of rain is forecast to fall up to 2,500′ with a foot of moist snow in the Alpine. Ridgetop winds will rise into the 40-50’s mph with stronger gusts from the east. Temperatures will continue to climb, ridgelines could see 32F while 1,000′ elevations, along the road at Turnagain Pass, may push to 40F.

Tomorrow: This storm will be slowly moving out tomorrow and light precipitation is expected with decreasing easterly ridgetop winds. Skies may clear enough to see the higher elevations. Weather models are showing another warm system impacting the region Tuesday night into Wednesday with continued rain/snow and wind.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	3	0.6	98
Summit Lake (1400′)	36	0	0.1	34
Alyeska Mid (1700′)	33	2	1.2	87

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	NE	34	71
Seattle Ridge (2400′)	30	*N/A	*N/A	*N/A

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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