Friday-Monday 2/23-26

Issued: Fri, Feb 23, 2018 at 8AM

Expires: Mon, Feb 26, 2018

With the potential for snow, winds could increase the windslab concern.

Above 2,500ft Considerable

1,800 to 2,500ft Moderate

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:   Touchy-Responsive
Distribution:   Specific
Likelihood (Human Triggered):   Likely
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):   
Possible
Size:   
Small – Large
Danger Trend:
   Decreasing
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:    Windslabs continue to build, and new ones building in areas they haven’t been observed in previous days.

The Feb. 22 storm brought 4″ to Valdez and 6″ to the pass and interior.  North winds will transport this new snow, creating notable windslabs lee of ridges and gullies.  The snowpack depth in any given area can vary widely now, with deep windslab formation over the last several weeks.

The combined effect of steady winds and sparse snow events is producing notable density differences in the upper snowpack.  The cold, clear weather of the past month between the 1/15 and 2/13 storms created a weak layer over the old snow and a poor bond for storm snow to adhere to. The old snow is a good, smooth bed surface. Moderate to high winds continue to transport snow in the upper elevations.

Persistent slabs are tricky to predict and generally carry higher consequences.  Our persistent slab concern still exists and our test pits indicate the primary layer of concern is buried 2-6′ (60-180cm) beneath the surface.  These layers are stubborn to trigger, but due to depth, will carry larger consequences.  We’re still tracking the distribution but suspect it could still be widespread, especially above 2500′.  Persistent layers will be easier to trigger near rocky outcrops and where snowpack is thinner.

Recent Avalanche Activity

No new observations but expecting to see natural activity today.

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F): 7 / 14
Ridgetop Wind Forecast (direction/mph): NE/6-35
Snowfall (in):  trace
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction   3 / All   21 / SE-NE
Max Wind Gust (mph) / Direction  8 / N  56 / NE
Temperature Min / Max (*F)  21 / 35  19 / 25

Weather Forecast:     Clear to broken skies today with a chance of trace of snow tonight.  Temperatures ranging in the teens and 20*F.  Winds gusting to 60mph.  Cloudy to broken cloud cover over the weekend with wind tapering.  0-2″ of snow expected.

Additional Info & Media

SNOW HISTORY: Valdez 2/23 AM Thompson Pass 2/23 AM
24 Hour Snow / Water Equiv. 3.9”/ 0.29″ 6″ / 0.5″
Storm Snow /Water Equiv. (2/22) 3.9” / 0.29″ 6″ / 0.5″
Current Snow Depth 37″ 83″
February Snow / Water Equiv. 25.5″ / 1.96″ 23″ / 2.3″
Total Winter Snowfall / Water Equiv. 103.64″ / 24” 313″ / 32.6″
Snowload in Valdez 52 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS / STORM TOTAL (Feb. 12) / STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): ” / ” / “
Upper Tsaina at 1750 ft (in): ” / ” / “
Sugarloaf at 550 ft (in): ” / ” / “
SNOW DEPTH & WATER SURVEY (2/5/2018) Depth Snow Water Equivalent
Milepost 2.5 Valdez  22″  7.6″
Milepost 18 32.5″ 9.6″
Milepost 29 Worthington Flats 62″ 19.4″
Milepost 37 Tsaina River bridge 52.6″ 16.4″
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