Saturday-Tuesday 2/18-21

Issued: Sat, Feb 18, 2017 at 8AM

Expires: Tue, Feb 21, 2017

First sun on soft snow can weaken bonds and lead to loose avalanche activity. Monitor those steep south faces above you taking in the solar radiation.

Despite calmer winds today, expect previous snow transport in exposed terrain and wind slab formation that is not quite bonded yet. Investigate before committing.

Above 2,500ft Considerable

1,800 to 2,500ft Moderate

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

SATURDAY SUNDAY MONDAY & TUESDAY

DANGER SCALE

 

LOOSE SNOW:
Elevation: All
Aspect: All
Terrain: All
Sensitivity: Responsive
Distribution: Wide Spread
Likelihood (Human Triggered): Possible
Size: Small – Large
Danger Trend: Steady
Forecaster Confidence: Fair

WIND SLAB:
Elevation: 
Above 1800′
Aspect: 
Mostly north and west
Terrain:
Near ridgelines, rollovers, and gully walls
Sensitivity:
Responsive
Distribution:
Specific
Likelihood (Human Triggered):
Likely
Size:
Small – Large
Danger Trend:
Decreasing
Forecaster Confidence:
Good

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: 

Since the 30″ of heavy new storm snow that fell last week, only 4 more fell with these last weak waves that didn’t push very far interior. Rain line from last week was observed as high as 2800′-3000′ near the Thompson Pass gap. Southeast winds picked up early February 14th and drifted the new storm snow. On Feb. 16, 2-8 inches of soft snow was sitting on top of rain crust, wind board, or even older surfaces. Add another 4 from the last couple days and there can be some great times had in wind protected areas. Some new soft wind slabs were cleanly sliding off weak thermal crusts, buried near surface facets and possibly even surface hoar more interior.  Human triggered avalanches are possible in steep, mid-upper elevation steeps that are windloaded. Remember, the further interior and north you get on the highway, the colder and thinner the snowpack, resulting in weaker basal facets at the ground. At least a couple avalanches beyond Milepost 33 (colder and thinner snowpack), that were naturally triggered in the storm, pulled out to ground facets.

Soft slab easily peeling off near surface facets. South facing on DOT ridge.

Snow has filled in and is sticking to rocks.

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. 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.

Below Baldy & Little Girls

Thin crowns at MP 33

Hippy Ridge: Widespread mid-elevation activity…weak layer likey recently buried surface hoar or facets. Upper elevations had blown back in.

  • Large deeper avalanche releases on basal weaknesses at the ground below Max Low and Wilbur’s on 40.5 Mile Ridge

Max Low released at rocks. Pit dug on Feb 8 right next to this crown.

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.

Forecaster: Kevin Salys