Sunday-Wednesday 2/26-3/1

Issued: Sun, Feb 26, 2017 at 8AM

Expires: Wed, Mar 01, 2017

Despite a low hazard day, maintain safe travel habits (1 at a time, limited exposure time, etc) and your situational awareness in avalanche terrain.

Avalanches are still possible in specific terrain, especially in higher elevations where wind loading on weak crystals is possible.

Above 2,500ft Low

1,800 to 2,500ft Low

Below 1,800ft Low

Degrees of Avalanche Danger ?

1. Low
2. Moderate
3. Considerable
4. High
5. Extreme

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

SUNDAY MONDAY TUESDAY & WEDNESDAY

DANGER SCALE

 

 

WIND SLAB:
Elevation:   
Above 3000′
Aspect:
   Various aspects due to shifting winds
Terrain:
 Near ridgelines, rollovers, and gully walls
Sensitivity:
 Responsive
Distribution:
 Specific
Likelihood (Human Triggered):
  Possible
Size:
 Small – Large
Danger Trend:
 Steady
Forecaster Confidence:
  Fair

AVALANCHE PROBLEM SCALE DESCRIPTORS:
Sensitivity: Non-reactive, Stubborn, Responsive, Touchy
Distribution: Isolated, Specific, Widespread
Likelihood: Unlikely, Possible, Likely, Nearly Certain
Size: Small, Large, Very Large (size scale <here>)
Danger Trend: Increasing, Steady, Decreasing
Forecaster Confidence: Good, Fair, Poor

AVALANCHE PROBLEM TOOLBOX <here>

SNOWPACK DISCUSSION:

intermountain-zone-iconInter-Mountain (Transitional) Specific: 

The February 13-15 storm deposited more than 30″ of heavy snow, mixed with rain below ~3000′, in the Thompson Pass region. A widespread avalanche cycle occurred during this storm, flushing out many persistent weak layers deeper in the snow pack. Make a mental note of where these large avalanches occurred, for areas that didn’t slide could still harbor problems.

The clear and cold spell February 18-22 created widespread surface hoar and near surface hoar (sugar snow or facets). Will these weaknesses remain when buried?  Faceted crystals can persist for a long time.

Crudbusters Surface Hoar to 6mm

As the sun rises ever higher above the horizon and hits previously shadowed terrain, consider the effects of solar radiation on southerly slopes. A slight change in slope angle in relation to the sun can impact the snowpack’s response dramatically. One can witness that the lower elevation steep southerlies above town and the airport have been warming and shedding due to the burning orb’s influence. Thick melt-freeze crusts on steep southerlies is predominant and providing a smooth bed surface to loose snow above.

Find more photos and observations at the bottom of the page. Sharing your observations creates an informed community that everyone benefits from at some point.

Recent Avalanche Activity

intermountain-zone-iconInter-Mountain (Transitional) Specific:  

Observed Feb. 18:

  • Numerous large(D3+) Wet Slab avalanches ran during the storm last week in the Tsania Valley that hit the valley floor
  • Natural Sluffs (Loose Snow) Observed on North Aspects in the Tsania Valley(before the glacier), while no natural activity was observed in the Tonsina Glacier area

Observed Feb 16:

  • Many mid storm avalanches released up to D2.5 off of steep faces: Several on north face of Odyssey, School Bus, Vertigo, Snatch, 40.5 Mile Ridge/Wilburs

Below Vertigo, crown filled in similar to Snatch and School Bus.

School Bus and North Odyssey Gully debris.

  • Extensive shallow slab releases on mid+ elevation southerly aspects below Bald Boy to Hippy Ridge (MP 29-37): seemed to be pulling out on persistent weaknesses: likely surface hoar or near surface facets formed last week.
  • Large deeper avalanche releases on basal weaknesses at the ground below Max Low and Wilbur’s on 40.5 Mile Ridge

Wilburs: lower central slab was deeper and looked like it pulled out to rocks.

Reported Feb.13-15 during the storm:

  • Large avalanches at Milepost 38, 42, and 50

Recent Weather

See Maritime Zone for updated weather.

Additional Info & Media

Weather Quicklinks:

  • NWS forecast for Northeast Prince William Sound <here>
  • NOAA NWS spot forecast for Thompson Pass <here>
  • Thompson Pass RWIS weather station <here>
  • MP 30 Nicks (Happy) Valley weather station at 4200 feet <here> (scroll to Nicks Valley)
  • Valdez Glacier UAF weather station at 6600 feet <data here> <map here>
  • Further weather resources <here>

SNOW CLIMATE ZONES:

  • coastal-zone-iconMaritime (Coastal) – from the Port of Valdez to Thompson Pass, all waters flowing into Valdez Arm and everything south of Marshall Pass.
  • intermountain-zone-iconInter-mountain (Transitional) – between Thompson Pass and Rendezvous Lodge.
  • interior-zone-iconContinental (Interior) – the dry north side of the Chugach (north of 46 Mile, including the Tonsina River).

Photo of Thompson Pass

thompson-pass-ski-runs

Interactive Map of Valdez Forecast Areas w/ Many Resource Layers (Trevor Grams)

climate-zones-topoclimate-zones-satellitegoogle-earth1

Run Map of Thompson Pass Area (Sean Wisner) (2MB download)
VAC Run Map Thompson Pass

NEWS: Our region is “one of the snowiest places on earth” – Serendipity / Rendezvous snowfall record set in 1963 <here>.

Free smart phone avalanche forecasts at: http://www.avalancheforecasts.com/

Posted in Intermountain Forecasts.
Pete Carter

Forecaster: Pete Carter