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Avalanche Advisory

Turnagain Area Avalanche Advisory
Forecaster:   Wendy Wagner  
Tuesday, March 26th 2013
Created: Mar 26th 6:45 am
3 Considerable Alpine / Above 2,500' Travel Advice: Dangerous avalanche conditions. Careful snowpack evaluation, cautious routefinding and conservative decision-making essential.
2 Moderate Treeline / 1,000'-2,500' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
2 Moderate Below Treeline / Below 1,000' Travel Advice: Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
 Show the Complete North American Avalanche Danger Scale
The Bottom Line

There is a CONSIDERABLE avalanche danger today near and above treeline for slab avalanches 1-3’ deep. These are most likely to be triggered on slopes over 35 degrees. Over the past 48 hours 1-2+ feet of low density snow has fallen on a variety of slick surfaces. Wind slabs formed by moderate NW winds yesterday and overnight are expected to be sensitive to a person. Also, expect any sunshine today to bring a slab character to the loose snow. In this case, soft slabs over a sun crust will have the potential to propagate and run to valley bottoms on southerly aspects.

Expert level snow assessment skills along with conservative terrain choices will be necessary for safe travel in avalanche terrain today. Safer areas to recreate are slopes 35 degrees and lower that are well away from runout zones.

Avalanche activity from yesterday:
We don't have a lot of information on yesterday's activity due to low visibility. What we do know is there were several naturally occurring medium sized avalanches in the Girdwood Valley due to heavy snowfall and wind that occurred mid-day. In Whittier there was a natural avalanche that hit and closed the Whittier tunnel (on the east portal, Whittier side). Last, on my field day to Turnagain Pass, small human triggered slabs and large sluffs were seen.


Primary Concern

The questions to answer if you are traveling in the backcountry today are (1) how much new snow has fallen, (2) does it have a slab character and (3) how is it adhering to the underlying surface(s)?

(1)  There have been significant differences in snowfall totals around the region (see mt. weather section below). The more snow the bigger the avalanche problem.

(2a)  Right now temperatures are cold - single digits - which is keeping much of the new snow loose (see secondary concern). However, winds picked up yesterday and last night from the NW and it does not take much to create soft wind slabs with this low density snow. Slabs have the potential to be very sensitive to humans and remotely triggered avalanches are possible. Watch for these on all slopes, rollovers and cross loaded gullies as terrain channeled winds can load every aspect.

(2b)  If the sun comes out and begins to warm the surface, watch for the loose snow to become more cohesive and form a soft slab. This is a concern on southerly aspects later in the day.

(3)  The old surface is a combination of slick sun crusts on the southerly half of the compass and a mixture of wind crusts and near surface facets (old loose powder) on the northerly half. The new snow is having a difficult time bonding with these surfaces. It will be prudent to give the new snow some time to settle and adjust.

Today is a tricky situation with the variety of underlying surface conditions. One person may ski a slope with only sluffing while the next person 30ft away may trigger an unmanageable slab.


Secondary Concern

Human triggered sluffs in the new snow will be likely today on all aspects. Expect these to entrain significant amounts of snow and run fast, especially on slopes with a sun or wind crust underneath. They also have the ability to trigger slab avalanches on the way down so be mindful of your terrain choices. Good sluff management techniques will be required and exit routes necessary.

Surface Conditions:
We have received our March refresher. Snow quality was excellent yesterday from all reports and should remain so today.


Mountain Weather

Snowfall shut off late last night in most areas around the Eastern Turnagain Arm. Below are totals from the past couple days:

                                                                  24 hr totals                       48hr totals

Turnagain Pass SNOTEL (1900’)                  5” (.4” water)                     7” (.6 water)
Turnagain Pass manual obs (2,500’)                6-8”                                     9-14”
Summit Lake (1400’)                                   5” (.4 water)                      7” (.5 water)
Alyeska (upper mountain)                               20+”                                    25-30”
Anchorage area – up to 18” on the upper hillside, official numbers HERE.
Hatcher Pass – up to 3’+ storm total, details HERE.

Winds associated with the snowfall were from the east during Sunday’s 6” then backed to the NW on Monday morning bringing in cold air and the majority of the snowfall. Overnight the NW to westerly wind picked up with hourly averages in the teens and gusts to 30mph. Skies are clearing this morning and temperatures are plummeting. Ridgetops are around 0F while sea level and treeline temps are in the single digits.

Today the low pressure centered over our region will head out with clearing skies. Temperatures should stay in the single digits and may climb into the teens at 1000'. Winds look to be in the 5-15mph range from the NW.

Tomorrow, the break in storms will continue but winds look to shift back to the southeast with warmer air moving in. Thursday, another system heads into the Gulf that should be a bit warmer.


 

Kevin will issue the next advisory tomorrow morning, March 27th.

 

This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area (this advisory does not apply to highways, railroads, or operating ski areas).

Winter snowmachine use open/closed status and riding conditions updates

Riding status is not associated with avalanche danger. An area will be open to motorized use in accordance to the Forest Management Plan when snow coverage is adequate to protect underlying vegetation. Backcountry hazards including avalanche hazard are always present regardless of the open status of motorized use areas.

(Updated: May 16, 2017 )

AREA STATUS WEATHER AND RIDING CONDITIONS
Glacier District
Johnson Pass: Closed
Placer River: Closed
Skookum Drainage: Closed
Turnagain Pass: ClosedThanks all for a safe and fun season on the Chugach NF! Stay tuned for the 2017/18 season. #playsafe #snowtosealevel
Twentymile: Closed
Seward District
Carter Lake: Closed
Lost Lake Trail: Closed
Primrose Trail: Closed
Resurrection Pass Trail: ClosedResurrection Pass trail will be open to snowmachine use during the 2017/18 winter season.
Snug Harbor: Closed
South Fork Snow River Corridor: Closed
Summit Lake: Closed

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The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur. This advisory provided by the Chugach National Forest, in partnership with Friends of the Chugach National Forest Avalanche Information Center.


USFS SNOW AND AVALANCHE HOTLINE (907) 754-2369
If you have comments or questions regarding CNFAIC operations or winter recreation management, please email staff@chugachavalanche.org
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