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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, November 22nd, 2013 - 7:00AM
Expires
Sat, November 23rd, 2013 - 7:00AM
Forecaster
Kevin Wright
Avalanche risk The Bottom Line

The storm that began yesterday afternoon produced a good bit of snow overnight.  We can expect a sharp increase in avalanche potential today, with that fresh snow overlying the old faceted weak snow that sat through the recent clear and cold stretch.  I expect a poor bonding interface and dangerous avalanche conditions above treeline today and into the weekend.  With a shallow snowpack there are still a lot of exposed rocks and trees that make avalanches and skiing somewhat more dangerous in the early season.

Fri, November 22nd, 2013
Alpine
Above 2,500'
3 - Considerable
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. 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
    Storm Slabs
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.
More info at Avalanche.org

New snow that started falling Thursday afternoon built up to at least 1 foot deep at higher elevations.  Snowfall amounts look fairly consistent between Girdwood and Turnagain Pass.  In addition, the temperatures shot up from single digits to the mid 30s this morning.  Wind peaked last night but continues to be strong this morning with gusts reaching 64mph at Sunburst.  Those 2 factors – rising temperatures and wind – will make the new snow “upside down” or denser on the top than the bottom and quite a bit heavier than the underlying layer.  This is a classic “unstable” setup.  

Given the current snowpack, storm snow avalanches likely started happening spontaneously last night.  We aren’t talking about a lot of snow yet, but it’s enough to warrant strong caution today and into the weekend.  With a tapering of the snowfall this morning we won’t be seeing a lot more natural activity, but human triggered avalanches will remain a problem today.  

Avalanche Problem 2
  • 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 ongoing wind is creating pockets of unstable snow in specific areas.  Sunburst has been reading wind averaging over 20mph and gusting over 60mph since the storm began.  Predominate wind direction at that site is from the East.  Seattle ridge has slightly less wind from an East Southeast direction.  That means West facing slopes and cross loaded North and South slopes are especially concerning.

Weather
Fri, November 22nd, 2013

With sea level temperatures currently in the mid 30s our snow has transitioned to rain in the lower elevations.  It also looks like the peak of this storm has passed for eastern Turnagain Arm but ongoing snow showers will continue for the next couple days.  Cooling temperatures are predicted which will transition the rain back to snow.  

Freezing rain in Anchorage and at sea level this morning is expected to cause travel difficulties.  Snow may become heavy at times in Anchorage this afternoon.

Schools in Girdwood and Seward are canceled today due to treacherous driving conditions!  Be safe out there!

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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.