Fri, November 29, 2019 Turnagain Pass Avalanche Forecast

Fri, November 29th, 2019

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.

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

Welcome to winter… ish. It’s currently 40F in Girdwood this morning. After two days of stormy weather precipitation is forecast to decrease today but easterly winds will remain fairly strong. Storm snow avalanches, including wind slabs along ridgelines, storm slabs in the sheltered zones, cornice falls and wet loose snow sluffs where rain is falling, should all be viewed as likely today. It’s a day to carefully evaluate terrain and consequences if an avalanche does release. The mountains need time to adjust.

Red flags to watch for:
– Recent avalanches – Are avalanches occurring today? Was there avalanche activity during the storm?
– Whumpfing (collapsing) of the snowpack
– Shooting cracks, likely to be seen near ridgelines where the wind has formed wind slabs.

Storm totals (beginning Wednesday through 6am Friday):

Turnagain Pass at 1,880′: 1.9″– of water equivalent, roughly 1.5-2′ of snow above treeline
Girdwood Valley at 1,700′: 3.6″ of water equivalent, roughly 2.5-3.5′ above treeline
Portage Valley at sea level: 5.3″ of water equivalent, roughly 5′ of snow above treeline
Summit Lake at 1,400′: 1.2″ of water equivalent, roughly 1′ of snow above treeline.

It is early in the season and overall we have limited snowpack data, especially in the Alpine (above 2500′) where most of the snow fell. What we do know is that the existing snowpack just got a heavy load. The storm was upside down with heavier snow falling on lighter snow or rain falling on snow. The winds were sustained and strong. Caution is advised. There is a long winter ahead. Don’t let early season stoke get the best of you!

Scouring and loading in the Tincan Alpine, 11.27.19

Weather

Fri, November 29th, 2019

Yesterday: Rain and snow fell throughout the day with snow line increasing to approximately 2200′ as temperatures rose well above freezing at lower elevations. In the past 24 hrs Girdwood received 1.5″ of water, Turnagain Pass 0.9″, and Portage (Bear Valley) 3.4″ with upper elevations seeing snow. Easterly winds were in the 30s with gusts into the 60s. Overnight temperatures were in the 40Fs at sea level, 30Fs at mid elevations and 20Fs at ridgetops.

Today: Rain and snow showers will continue today with snow line forecast to be around 2400′, 0.3 inches of water and 0-6″ of snow. Temperatures will be in the low 40Fs at sea level and the high 20Fs along ridgetops. Winds are forecast to be easterly 15-35 mph with gusts into the 50s. Overnight temperatures should cool a bit and rain/snow showers will continue with snow line dropping to 1500′. Winds will remain easterly gusting into the 40s.

Tomorrow: Cloudy skies with rain and snow showers and daytime temperatures just slightly cooler than today. Easterly winds will decrease to 5-10 mph. The pattern looks to remain active into next week with an overall cooling trend.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	35	1	0.9	15
Summit Lake (1400′)	34	0	0.3	8
Alyeska Mid (1700′)	33	5	1.44	20

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	NE	32	68
Seattle Ridge (2400′)	NA*	SE*	15*	35*

*Seattle Ridge is not recording temperature and wind stopped recording at 10 pm.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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