Thursday-Sunday 2/23-26

Issued: Thu, Feb 23, 2017 at 8AM

Expires: Sun, Feb 26, 2017

Stay tuned in to changing snowpack conditions at the surface.

Expect new windslabs drifted onto a variety of slopes by variable winds. These are likely forming on top of widespread weak crystals from our long clear, cold spell.

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

THURSDAY FRIDAY SATURDAY & SUNDAY

DANGER SCALE

 

WIND SLAB:
Elevation:   Above 3000″
Aspect:  Various aspects due to shifting winds
Terrain:   Near ridges, gullies, rollovers
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:

Maritime (Coastal) Specific: 

About an inch of soft snow has been added to the foot plus of dry snow from last week. All of this is resting on mid February’s rain crust down low, which transitions to firm slabs above the rain line ~2600′. A recent uptick in winds have started to drift and move the surface snow around more, especially on higher, exposed ridgelines.

A generally stable snowpack could shift as winds form new slabs over weak surface crystals. Over the long calm, clear and cold spell last weekend, widespread surface hoar and near surface facets formed throughout our region. Investigate how these weak crystals are reacting after being buried by firmer wind layers above. Evaluate and test new slabs readily, for these buried crystals can persist and lead to problems for extended periods of time….leading to unpredictable and large avalanches.

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 are warming and shedding due to the burning orb’s influence.

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

Maritime (Coastal) Specific: 

  • 2/13-14: Numerous wet avalanches below the rain line (+-3000′) around the Port.
  • 2/18: Natural sluff avalanches (loose snow) observed on sunny south facing aspects from solar radiation.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  16 / 28
Ridgetop Wind Forecast (direction/mph):  Var / 10-20
Snowfall (in/water equivalent):  0″ / 0″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  4 / NE  ? / NE
Max Wind Gust (mph) / Direction  11 / ENE  ? / NE
Temperature Min / Max (*F)  18 / 27  ? / ?

Weather Forecast:    A large high pressure system sitting in the Gulf of Alaska is bringing in warmer air to our region. High clouds will linger and slowly dissipate late today as fronts push in from the west.  Some moisture seems it will sneak around and hit us later Friday followed by high clouds Saturday night. There will be some short periods of clearing in between these waves of moisture affecting our region.

Additional Info & Media

SNOW HISTORY: Valdez 2/23 AM Thompson Pass 2/23 AM
24 Hour Snow / Water Equiv. <1″/0.1″ Trace /0.01″
Storm Snow /Water Equiv. (2/17-2/18) 0.59” /0.5″ 3″ /0.3″
Current Snow Depth 48″ 48″
February Snow / Water Equiv. 44.9″ /5″ 42″ / 5.0″
Total Winter Snowfall / Water Equiv. 222.8″ /20.9” 281″ / 27.6″
Snowload in Valdez 78 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS (2/23 AM)/STORM TOTAL (2/22-23)/STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): 0″ / 0″ / 0″
Upper Tsaina at 1750 ft (in): 0″ / 0″ / 0″
Sugarloaf at 550 ft (in): <1″/ 1″ / 0.1″
SNOW DEPTH & WATER SURVEY (2/1/2017) Depth Snow Water Equivalent
Milepost 2.5 Valdez  41.5″  9.8″
Milepost 18 43.9″ 9.5″
Milepost 29 Worthington Flats 61.5″ 16″
Milepost 37 Tsaina River bridge 42.1″ 9.3″
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 Maritime Forecasts.

Forecaster: Kevin Salys