Tuesday-Wednesday 4/24-4/27

Issued: Tue, Apr 24, 2018 at 8AM

Expires: Fri, Apr 27, 2018

Above 2,500ft Moderate

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

Tuesday Wednesday Thursday & Friday

DANGER SCALE

Storm Snow (once a foot more new snow accumulates):
Elevation:   Above 2500′
Aspect:   All
Terrain:   All avalanche terrain
Sensitivity:   Responsive
Distribution:   Widespread
Likelihood (Human Triggered):     Nearly Certain
Size:   Small – Large 
Danger Trend:   Increasing
Forecaster Confidence:    Good   (if weather forecast is accurate)

Wind Slab (once a foot more new snow accumulates):
Elevation:
   Above 2500′
Aspect:
   W-N
Terrain:
   Lee of ridges, gullies, ridge tops exposed to wind
Sensitivity:
   Responsive
Distribution:
   Specific
Likelihood (Human Triggered):
   Likely
Size:
   Small – Large
Danger Trend:
   Increasing
Forecaster Confidence:
    Fair   (if weather forecast is accurate)

Wet Avalanches:
Elevation:   Below 2500′
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 rain
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:     An estimated 4-6″ of new snow has accumulated above 3000′ elevation by 4/24 Tuesday morning at the front end of the storm. On Friday 4/20, the advisory area above 2500′ received 5″ snow, with 8″-12″ observed accumulated at 5000′ elevation on Loveland Glacier at Milepost 27.  Near Thompson Pass, southeast wind transported the new snow into small windslabs 3″-8″ deep lee of ridges, gullies and ridge tops. With warm temps, these windslabs are bonding to old surfaces.

Our diurnal spring shed cycle is in progress.  Temperatures around Thompson Pass have been above freezing during the day, with the surface of the snowpack freezing over night.  This cycle produces corn snow, but is also drives surface instability and isothermic snowpack (rotten moist snow that is all zero celcius).

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 facing slopes 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

No new observations.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 23 / 32
Ridgetop Wind Forecast (direction/mph): SE/20-40
Snowfall (in):  5-14”
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  5 / N   25 / SE
Max Wind Gust (mph) / Direction  9 / N  35 / SE
Temperature Min / Max (*F)  37 / 43  25 / 33

Weather Forecast:      Snowfall above the freezing level hovering 2000′-2500′ elevation. Quite a lot of snowfall possible, maybe four feet by the weekend, with maybe three inches of rain at sea level accompanied with strong onshore southerly winds.

Additional Info & Media

SNOW HISTORY: Valdez 4/21 AM Thompson Pass 4/24 AM
24 Hour Snow / Water Equiv. 0”/ 0.0″ 1″ / 0.2″
Storm Snow /Water Equiv. (4/21-24) 0” / 0″ 7″ / 0.5″
Current Snow Depth 10″ 62″
April Snow / Water Equiv. 0″ / 0.01″ 7″ / 0.7″
Total Winter Snowfall / Water Equiv. 132.59″ / 27.21” 380″ / 37.4″
Snowload in Valdez ~ 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