Wednesday-Saturday 4/18-4/21

Issued: Wed, Apr 18, 2018 at 8AM

Expires: Sat, Apr 21, 2018

Valdez Snowmachine Club Hill Climb this weekend

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

Wednesday Thursday Friday & Saturday

DANGER SCALE

Wet Avalanches:
Elevation:   Below 4500′
Aspect:   SE – S – SW
Terrain:   Southerly facing terrain on slopes above 30 degree slope angle
Sensitivity:   Non-reactive when frozen – Responsive when warmed by above freezing temps and direct solar input
Distribution:   Specific
Likelihood (Human Triggered): Possible
Size:   Small – Large
Danger Trend:   Increasing with solar input and above freezing temperatures
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

LIST OF AVALANCHE PROBLEMS <here>

SNOWPACK DISCUSSION: The annual spring shed cycle is well underway.  Temperatures around Thompson Pass have been above freezing during the day, with the surface of the snowpack freezing over night.  This cycle can produce corn snow but is also the precursor to surface instability and an isothermic snowpack.

Snow surface conditions above ~3000′ are widely variable.  Conditions on northerly facing slopes range from wind scoured pencil hard sastrugi, melt/freeze, to decomposing unconsolidated particles.  Southerly faces are experiencing a range from heavy wet snow, to melt freeze crusts, to corn, to isothermal.

Snow depths generally range from 30-300cm, including on glaciated terrain.

Check out our public observations.

Recent Avalanche Activity

From the port of Valdez up to 4500′ throughout the advisory area: numerous southerly facing slopes above 30* slope angle have begun the spring shed with natural wet avalanches. This wet avalanche activity has been triggered by daytime temperatures above freezing and direct solar input.  Many have been initiating in rocky steeps, taking surface snow, but some have stepped down to deeper old layers, pulling out small slabs with them.

Friday & Saturday 4/13 & 14 PM: wet snow avalanches at Three Pigs at Milepost 39 ran to the middle of the highway.

While the snow is frozen, the avalanche danger is low with natural and human triggered avalanches unlikely. As the day heats up and solar input increases, the snow warms and avalanche danger rises with human and natural triggered avalanches likely.

Video of Winds from 3/22/18

 

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 20 / 33
Ridgetop Wind Forecast (direction/mph): E/20
Snowfall (in):  0”
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  4 / NE   20 / SE
Max Wind Gust (mph) / Direction  12 / NE  30 / SE
Temperature Min / Max (*F)  33 / 42  12 / 30

Weather Forecast:      Cloudy Wednesday with an increasing chance of snow flurries Thursday with maybe an inch to a few inches accumulating through the weekend. Dirunal spring temperatures with warm days and overnight freezes. Light winds throughout.

Additional Info & Media

SNOW HISTORY: Valdez 4/18 AM Thompson Pass 4/18 AM
24 Hour Snow / Water Equiv. 0”/ 0.01″ 0″ / 0.0″
Storm Snow /Water Equiv. (3/15-19) 19” / 0.41″ 40″ / 1.5″
Current Snow Depth 12″ 63″
April Snow / Water Equiv. 0″ / 0.01″ 1″ / 0.1″
Total Winter Snowfall / Water Equiv. 132.59″ / 27.21” 373″ / 36.7″
Snowload in Valdez 30 lbs/sq. ft.

 

SNOW DEPTH & WATER SURVEY (3/4/2018) Depth Snow Water Equivalent
Milepost 2.5 Valdez  32.2″  9″
Milepost 18 42″ 11″
Milepost 29 Worthington Flats 62.4″ 21.2″
Milepost 37 Tsaina River bridge 58.4″ 14.2″
This survey is done the first week of each month.

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 Continental Forecasts, Intermountain Forecasts, Maritime Forecasts.
Pete Carter

Forecaster: Pete Carter