Thursday-Sunday 4/6-4/9

Issued: Thu, Apr 06, 2017 at 8AM

Expires: Sun, Apr 09, 2017

As warm temperatures continue to push ever so higher with rain, consider the transition to loose, wet avalanche conditions in steep terrain.

Friday April 14 bon fire: VAC Full Moon FUNraiser with Acoustic Avalanche at the Tsaina Lodge

Above 2,500ft Moderate

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

THURSDAY FRIDAY SATURDAY & SUNDAY

DANGER SCALE

STORM SLAB:
Elevation:
  Above 2500′
Aspect:
 All, but loaded deeper on slopes lee to onshore wind
Terrain:
Wind protected
Sensitivity:
   Responsive
Distribution:
   Widespread, minus scoured slopes.
Likelihood (Human Triggered):
   Possible
Size:
  Small – Large
Danger Trend:
   Decreasing
Forecaster Confidence:
   Fair

WET LOOSE:
Elevation:
   Below 5000′
Aspect:
 Southerlies: W-E
Terrain:
Steep terrain near rocks and vegetation.
Sensitivity:
   Responsive
Distribution:
   Specific.
Likelihood (Human Triggered):
   Possible
Size:
  Small
Danger Trend:
   Increasing each day with warming temperatures
Forecaster Confidence:
   Fair

WIND SLAB:
Elevation:
  Above 2500′
Aspect:
aspects lee to south-east storm wind
Terrain:
shallow snowpack near ridges, rollovers, gullies with facets underneath
Sensitivity:
   Responsive
Distribution:
   Specific.
Likelihood (Human Triggered):
   Possible
Size:
  Small – Large
Danger Trend:
   Decreasing
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 last series of storms moved in from March 27- through today with little clearing and sunny weather in between….despite lulls in precipitation. The fronts have pushed in with minimal power (as has been the trend for the season), strongly favoring the maritime for precipitation: snow totals nearing 4′ versus 3′ up on the pass. Recent reports show that depths have settled down to 3′ in the maritime and 2′ on Thompson Pass as of Wednesday.

Winds during this series have mostly been strong SE onshore with short stints shifting offshore out of the NE. Reports have supported minimal ridgetop winds when you get off the major pass corridors that funnel the flows. This has resulted in moderate scouring and loading of the new snow in specific terrain features that have been exposed to the primary southerly winds. Firm windslabs have been found just below ridgelines and have been sensitive and collapsing on occasion. The warm and sticky snow has also led to some growth of cornices lee to onshore wind.

Warm pacific air and green-housing temperatures have brought in a dramatic shift from the arctic outflows prior to late last month. Rain has pushed up to around 3000′ on the pass and even higher in the maritime….3600′. On Tuesday, above freezing temperatures hit near 4500′ on the north side of the pass and up to 5500′ in the maritime. These warming temperatures led to wet loose activity up to 3600′ and even higher on southerly radiated slopes. Consider diurnal repeats of this scenario as temperatures rise ever so higher and impact dry snow with little strength. This also has led to some firming of the snow surface resting on dryer, weaker snow.

In general, the newest storm snow has been bonding well to old layers, while facets have been the exception. Areas that held near surface facets have demonstrated to be reactive, mostly on westerly and southerly aspects, where radiation could very well be weakening the bond at the old-new interface.  Shady, colder northerlies have seen more of a problem with resistant planar sheers at interfaces (2 at 4800′  below Goodwills) within the new snow….temperatures shifts mid-storm that have resulted in preserved decomposing fragments that have yet to bond solidly. Depths vary depending on where you are. While recent snow test results have not supported propagation, smaller avalanches up to D2 have been human triggered in various areas on the interfaces mentioned above. See observations and recent activity in the forecast for this upper elevation activity.

Persistent slab problems are still a serious concern in colder, thinner and more continental areas. The structure is very poor and the potential for a storm slab or hard slab to step down to weak basal facets is scary. Continue to monitor this structure as temperatures rise and weaken the firmer, overlaying structure.

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:  

  • April 3 small D1 avalanches triggered on southerly aspects at high elevations.
  • April 3: Hard wind slab collapse reported near the top of couloirs/ridgeline
  • April 2: human triggered small (D1) wind slab avalanche reported on a southerly aspect, released from thin coverage on rocks above
  • March 31: D2 human triggered avalanche on N aspect at 3500′

Recent Weather

See Maritime Zone for updated weather.

Additional Info & Media

Weather Quicklinks:

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