Friday-Monday 1/20-1/23

Issued: Fri, Jan 20, 2017 at 8AM

Expires: Mon, Jan 23, 2017

Even though winds have let up and less snow is available for transport than yesterday, freshly formed wind slabs will still slowly build and remain sensitive due to continued winds and cold temperatures.

 

Safe travel techniques and planning involve talking about how to manage larger than expected avalanches and sufficient gear to hunker down in the cold for a period of time if necessary. It will slowly warm up today, but it was -27*F at the upper Tsaina River and -8*F on Thompson Pass this morning.

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

FRIDAY SATURDAY SUNDAY & MONDAY

DANGER SCALE

WIND SLAB:
Elevation:
 Above 1800′
Aspect: Shifting winds have loaded (top and cross-loaded) all aspects exposed to wind in the last week
Terrain:
Ridges, gullies, bowls, rollovers
Sensitivity:
 Touchy
Distribution:
 
Specific
Likelihood (Human Triggered): 
Likely
Size:
 Large
Danger Trend: 
Decreasing slowly
Forecaster Confidence: 
Good

PERSISTENT SLAB:
Elevation: 
Mostly above 2500′
Aspect: 
All
Terrain: 
Steep rocky slopes where facets exist under old and between windslab, especially interior of Thompson Pass
Sensitivity: 
Stubborn
Distribution: 
Specific
Likelihood (Human Triggered): 
Possible
Size: 
Small – Large
Danger Trend: 
Steady 
Forecaster Confidence: 
Poor

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

LIST OF AVALANCHE PROBLEMS <here>

SNOWPACK DISCUSSION: The 54 inches of snow that fell Jan 13-17 settled quickly if it wasn’t blown away into windslab. Now, to seal the deal and firm up our surfaces, a strong northeast wind has once again wreaked havoc on our mountain slopes leading to natural avalanche activity Thursday.  Everything on the pass is scoured and wind textured.

Wind Scoured Pass

Wind Scoured Pass

Wind Scoured Odyssey

Wind Scoured Odyssey

Expect firm windslab depths to 3 feet or more on lee features. In semi-protected areas, soft windslabs were easily sliding off of steep rollovers on Wednesday. The cold temperatures, near or below zero F, at Thompson Pass and inland will slow the bonding of fresh windslab to old surfaces.

In wind protected areas, the storm snow has settled quickly and has formed a soft, supportable slab with wind skin in areas. Luckily, the recent storm snow seems to be bonding quite well despite its weak nature in relation to overlying new windslabs. Failures have been non-planar breaks that won’t support propagation.

In the lower part of the firm midpack, below our knife-hard wind slabs from early this year, old facets are firming and tending to holding tight to each other.

Most unsettling are scattered areas with a structurally weak base of sugar snow that is precariously holding up heavy mid and upper slab layers. Large whumphs were reported Tuesday near the Worthington Glacier, reminding us we cannot fully trust this snowpack yet: especially in areas that are colder with a thin snowpack (inland of MP 33 where these conditions are more likely to be found).

It is still possible for smaller upper layer avalanches to step down to deep old persistent weak layers and create very large events.

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

Many upper elevation, exposed areas were dramatically scoured revealing several storm-related, loose dry avalanches in very steep, rocky terrain throughout the road corridor. Post-storm, strong outflow winds led to many fresh wind slabs peeling off Thursday. Significantly less snow hit the continental and northern part of the inter-mountain zones, leading to much loading and avalanche activity. Please share what you see.

coastal-zone-iconMaritime (Coastal):

  • Dec. 19: Wind slab release during the day above the airport and below South Odyssey Coulior
Windslab release off ridge above airport

Windslab release off ridge above airport ran to alders (lines mark crown and toe of debris)

  • Dec. 17: Reported mid-storm debris below the N face of Benzine sliding into the popular ski line. Many others seen in steep gullies.

intermountain-zone-iconInter-Mountain (Transitional):  

  • Dec. 19: Several new wind slab releases in windloaded gullies below Max High
Release Near Max High

Release Near Max High

Old debris seen day before off summit of Max High, but today wind slabs peeling out in loaded gullies.

Old, storm related avalanche ran off summit of Max High (see arrow), but Thursday’s wind slabs peeled out in loaded gullies below (see crown lines).

  • Dec 18: Max High Peak had some old-ish (mid-storm?) debris below the SE aspect at about MP 35 (see Trevor’s map link below for location)

interior-zone-iconContinental (Interior):

MP 51 Boulder Creek/Rice Mountain Release to ground.

Dec 19: MP 51 Boulder Creek/Rice Mountain Release to ground. Possibly storm initiated, for debris in gully seemed filled in.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  5 / 21
Ridgetop Wind Forecast (direction/mph): ENE / 5-20
Snowfall (in):  Trace
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction   10/ NE  26 / NE
Max Wind Gust (mph) / Direction  23 / ENE  47 / NE
Temperature Min / Max (*F)  5 / 17  -11 / -3

Weather Forecast:  A weak low pushing across mainland Alaska will usher in a gradual warming of temperatures and building clouds this afternoon. Models are not in agreement as to the path and amount of water this front could bring us, but scattered flakes could hit us tonight. It won’t do much in changing the outflow winds besides aiding in lowering the velocity. Expect a variety of broken skies until a large low introduces a warm front that should hit us Monday afternoon/evening.

Additional Info & Media

SNOW HISTORY: Valdez 1/20 AM Thompson Pass 1/20 AM
24 Hour Snow / Water Equiv. 0” /0” 0″ /0″
Storm Snow /Water Equiv. (1/13-1/17) 46.4” /3.2″ 54″ /4.2″
Current Snow Depth 40″ 36″ (wind scoured)
January Snow / Water Equiv. 46.4″ /3.2″ 54″ / 4.2″
Total Winter Snowfall / Water Equiv. 142.3″ / 13” 197″ / 18.6″
Snowload in Valdez 47 lbs/sq. ft.

 

SNOWFALL for LAST 24 HRS at OTHER STATIONS:
Nicks Valley at 4200 ft (in): 0″
Upper Tsaina at 1750 ft (in): 0″
Sugarloaf at 550 ft (in): 0″
SNOW DEPTH & WATER SURVEY (1/3/2017) Depth Snow Water Equivalent
Milepost 2.5 Valdez  22.7″  4.7″
Milepost 18 27.9″ 5.9″
Milepost 29 Worthington Flats 44″ 9.9″
Milepost 37 Tsaina River bridge 33.8″ 5.6″
This survey is done the first week of each month.

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 VAC Forecasts.

Forecaster: Kevin Salys