Friday-Monday 2/17-20

Issued: Fri, Feb 17, 2017 at 8AM

Expires: Mon, Feb 20, 2017

Even more snow and strong onshore winds out of the SE will form sensitive wind slabs on lee terrain features.

Use small terrain as test pieces and investigate for the existence of persistent weaknesses in more interior, continental snowpack.

Tomorrow, February 18, Kyle Sobek is leading a Backcountry & Avalanche Riding Safety Field Session. 9am-4pm. More details. Learn READY RIDER skills.

Above 2,500ft Considerable

1,800 to 2,500ft Moderate

Below 1,800ft Moderate

Degrees of Avalanche Danger ?

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

Avalanche Danger Rose ?

Avalanche Problems ?

Problem Details

FRIDAY SATURDAY SUNDAY & MONDAY

DANGER SCALE

 

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

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: 
Increasing
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: 

With ~30″ of heavy new storm snow in the last 5 days and another possible foot on the way, start zones are primed to release storm snow and wind slab avalanches. Rain line 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. Some new soft wind slabs were cleanly sliding off weak thermal crusts, buried near surface facets and possibly even surface hoar more interior.  At least a couple avalanches beyond Milepost 33 (colder and thinner snowpack), that were naturally triggered in the storm, pulled out to ground facets. Human triggered avalanches are likely in steep, mid-upper elevation steeps that are windloaded.

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