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ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, April 28th, 2013 - 7:00AM
Expires
Mon, April 29th, 2013 - 7:00AM
Forecaster
Wendy Wagner
Avalanche risk The Bottom Line

Most terrain around the Eastern Turnagain Arm has LOW avalanche danger this morning. Below treeline, the danger will rise to MODERATE late in the day for human triggered wet loose avalanches as temperatures climb. Additionally, there are pockets of MODERATE danger on steep upper elevation slopes where it is possible to trigger a shallow stiff wind slab just below ridgelines.

For Monday, avalanche conditions look to be similar to today. Keep in mind, if warm wet weather moves in mid-week you can expect the avalanche danger to rise.

Special Announcements

Today will be our final advisory for the season. Stay tuned for a springtime avalanche concern write up and a brief season recap on May 1st. Also, our annual report will be coming out in the next week or so – watch for that on our resources page.

But most importantly: A huge THANK YOU to all of our supporters, donators and observers for making the Chugach National Forest Avalanche Center a reality. We could not do it without you!!

Sun, April 28th, 2013
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
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. Dangerous avalanche conditions. 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
  • Wind Slabs
    Wind Slabs
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.
More info at Avalanche.org

The north winds have ravaged the upper elevations. We continue to hear of parties feeling collapsing and whoomphing on ridgelines and some able to trigger slabs 2-6″ thick. These slabs may be shallow but they are stiff and can be dangerous if triggered in ‘no fall’ zones (i.e., over cliffs). Since most of the higher terrain has significant wind affect, you are likely to find many areas with a breakable and annoying wind crust along with the scattered areas of wind slab. Unsupported slopes are the most concerning (see the second photo for an example of this). Our unusually cool spring has allowed the facets below these slabs to persist and wintertime cold snow issues to remain above treeline.


Photo is of Graham Predeger monitoring the breakable wind crust Saturday that covers most upper elevation slopes. This is near the top of the Burns glacier ~4,000ft.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
More info at Avalanche.org

Below treeline today, and on southerly aspects with little wind, you can expect the crusty surfaces to warm up late in the day. The cool temperatures and breeze may keep warming limited, however if you do come across a slope with more than 6 inches of mushy wet snow avoid it. If this is the case triggering a wet loose snow avalanche is quite possible and can entrain a lot of heavy snow and run far.

Below is a photo from Saturday. The wet avalanche activity is a few days old (from Tues/Wed) but the picture demonstrates what our mountains look like and the variable nature of the snow conditions.

 

The much anticipated “shed cycle” has not produced yet and maybe this will be one of those years we don’t really see it. The cool northerly flow and clear nights has kept the pack from warming up. However, we do have a warmer system moving in this week so keep your eye out any avalanche activity associated with this.

Weather
Sun, April 28th, 2013

Sunny skies prevailed once again yesterday. Winds were light from the northwest in the 5-10mph range. Temperatures climbed to the mid 20’sF on the ridgelines and low 40’sF at 1,000′.

Today should be another brilliant day in the backcountry with the only change being breezier northerly winds. The winds kicked up last night (averaging 10mph gusting 23mph on Sunburst and bit more at Seattle Ridge) and will be on a slow decrease today. Expect ridgetops to blow in the 10-15mph range with gusts to 30mph from the north. Temperatures will again climb into the 20’sF at the upper elevations and ~40F at 1,000′.

For Tuesday into Wednesday look for a change in the pattern. Models are showing a shift back to a moist southwest flow with the approach of a low pressure system in the north Pacific. Warmer temperatures, clouds and precipitation should return to the Eastern Turnagain Arm.

Helpful weather links:
CNFAIC weather page
MountainWeather.com’s Alaska Page  


This wraps up our final advisory for the season. We will be updating this page around May 1st with springtime avalanche concerns so check back mid-week. Thanks!

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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.