Saturday-Tuesday 3/10-3/13

Issued: Sat, Mar 10, 2018 at 8AM

Expires: Tue, Mar 13, 2018

If winds pick up and snow is transported, the danger rating could rise quickly.  Be mindful of other riders and regroup out of harms way.

Above 2,500ft Considerable

1,800 to 2,500ft Considerable

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

Friday Saturday Sunday
& Monday

DANGER SCALE

 

WIND SLAB:
Elevation:   Above 2000′
Aspect:   Lee of ridges, gullies, ridgetops
Terrain:   Upper elevation terrain exposed to wind
Sensitivity:   Responsive
Distribution:   Specific
Likelihood (Human Triggered):   Possible
Size:   Small – Large
Danger Trend:   Increasing
Forecaster Confidence:   Fair

PERSISTENT SLAB:
Elevation:
   Above 2500′
Aspect:
   All  
Terrain: 
  35+ degrees steepness
Sensitivity:
   Stubborn
Distribution:   
Specific
Likelihood (Human Triggered): 
 Unlikely
Size:   
Small – Large
Danger Trend:
   Decreasing
Forecaster Confidence:
   Poor

STORM SNOW:
Elevation:
   All
Aspect:
   All  
Terrain: 
  35+ degrees steepness
Sensitivity:
   Responsive
Distribution:   
Widespread
Likelihood (Human Triggered): 
 Likely
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

LIST OF AVALANCHE PROBLEMS <here>

SNOWPACK DISCUSSION: 

The advisory area received 5-8″ (12-20cm) of snow on Friday.  The interface of this new snow with the old snow surface is weak due to the significant density differences between the two.

Extreme winds  Feb. 28 – Mar. 1 scoured exposed terrain and eroded into older snow layers.  The snowpack depth varies widely due to these wind events scouring the snowpack down to rock and heather, while just lee of ridges there are pockets of windslab meters deep.

The combined effect of steady winds and sparse snow events has produced notable density and depth differences in the upper snowpack.  The cold, clear weather between the 1/15 and 2/13 storms grew a weak layer which the subsequent storm snow did not adhere to very well.

Due to that layer of facets 2-6′ (60-180cm) beneath the surface, a persistent slab concern still exists. We’re still tracking the distribution above 2500′ and our recent snowpit tests are indicating this layer may no longer be a widespread concern.  The bottom line is that these persistent weak layers are stubborn to trigger, but due to depth, will have higher consequences if a rider, or riders, find the trigger point; be cautious near thinner areas, and rocky outcrops.

 

Recent Avalanche Activity

Two natural D1 windslab avalanches observed near miles 23 and 25 of the road corridor on Friday.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 17 / 24
Ridgetop Wind Forecast (direction/mph): SE /8-25
Snowfall (in):  Trace – 2″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  3 / Variable   22 / SE
Max Wind Gust (mph) / Direction  19 / E  41 / SSE
Temperature Min / Max (*F)  15 / 37  18 / 21

Weather Forecast:   Saturday mostly cloudy with snow showers possible in the afternoon.   Sunday and Monday may produce snow totals over 12″ (30cm).  Temperatures in the teens and twenties during the forecast period with light winds continuing to converge near Thompson pass from the north and south.

Additional Info & Media

SNOW HISTORY: Valdez 3/10 AM Thompson Pass 3/9 AM
24 Hour Snow / Water Equiv. 5.1”/ 0.35″ ?″ / ?″
Storm Snow /Water Equiv. (3/10) 5.1” / 0.35″ ?″ / ?″
Current Snow Depth 37″ 69″ wind scoured
March Snow / Water Equiv. 9.3″ / 0.55″ 2″ / 0.1″
Total Winter Snowfall / Water Equiv. 123.3″ / 25.21” 325″ / 33.1″
Snowload in Valdez 47 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.

Forecaster: Ryan Van Luit