Saturday-Tuesday 2/18-21

Issued: Sat, Feb 18, 2017 at 8AM

Expires: Tue, Feb 21, 2017

First sun on soft snow can weaken bonds and lead to loose avalanche activity. Monitor those steep south faces above you taking in the solar radiation.

Despite calmer winds today, expect previous snow transport in exposed terrain and wind slab formation that is not quite bonded yet. Investigate before committing.

Above 2,500ft Considerable

1,800 to 2,500ft Moderate

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

SATURDAY SUNDAY MONDAY & TUESDAY

DANGER SCALE

 

LOOSE SNOW:
Elevation: All
Aspect: All
Terrain: All
Sensitivity: Responsive
Distribution: Wide Spread
Likelihood (Human Triggered): Possible
Size: Small – Large
Danger Trend: Steady
Forecaster Confidence: Fair

WIND SLAB:
Elevation: Above 2000″
Aspect: Lee to SE wind
Terrain: Near ridges, gullies, rollovers
Sensitivity: Responsive
Distribution: Specific
Likelihood (Human Triggered): Possible
Size: Small – Large
Danger Trend: Decreasing
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

AVALANCHE PROBLEM TOOLBOX <here>

SNOWPACK DISCUSSION:

Maritime (Coastal) Specific: 

13 inches of snow was added to the 3.62+” water equivalent in the last 6 days. The snowpack absorbed large amounts of moisture and settled extensively with the rain event from early last week. This storm was a classic crush and flush topped off with a foot of snow icing to the cake; old instabilities will not be a concern in this maritime zone after this weather has run it’s stint. Make sure you evaluate how the new snow is bonding to old, icy surfaces and investigate mid-storm instabilities. Warm high temperatures the last couple days has aided in the bonding of layers.

In the upper elevations, during windows of visibility in last week’s storm, flagging of moving dry snow off the peaks in the port was seen. This points to previous wind slab formation in the colder elevations above the rain line….estimated at ~3000′.

Snow has filled in and is sticking to rocks.

Soft slab easily peeling off near surface facets. South facing on DOT ridge.

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: 

Observed Tuesday February 14:

  • wet avalanches to size 2.5 ran full track to sea level between Mineral Creek and Shoup Bay
  • wet avalanches to size 2 off Benzene Peak near Solomon
  • wet avalanches to size 2 fell off steeps of Keystone Canyon
  • wet avlaanches to size 2 ran into Snowslide Gulch above MP 15-16

Recent Weather

WEATHER FORECAST for NEXT 24 HRS at 3,000 ft:
Temperature Forecast (Min/Max *F):  10 / 23
Ridgetop Wind Forecast (direction/mph):  SE / 10-20
Snowfall (in/water equivalent):  Trace / 0.08″
WIND & TEMPERATURE
PAST 24 hours
Ferry Terminal Thompson Pass
Average Wind Speed (mph) / Direction  3 / NE  15 / SE
Max Wind Gust (mph) / Direction  12 / NE  34 / SE
Temperature Min / Max (*F)  28 / 33  19 / 23

Weather Forecast:  While the precipitation dried up and skies have parted already late yesterday on the interior side of the pass, expect the same to follow in the maritime throughout the day today. Temperatures at Mile Post 46 are already in the single digits and cooling will slowly ensue over the next day in town. The outlook is seeming quite clear with periods of clouds lasting well into next week. Winds will be light out of the south today until they could shift Sunday and pick up a bit on Monday.

Additional Info & Media

SNOW HISTORY: Valdez 2/19 AM Thompson Pass 2/18 AM
24 Hour Snow / Water Equiv. 0”/0″ 3″ /0.3″
Storm Snow /Water Equiv. (2/17-2/18) 3.1” /0.2″ 4″ /0.4″
Current Snow Depth 56″ 53″
February Snow / Water Equiv. 44.2″ /4.5″ 40″ / 4.8″
Total Winter Snowfall / Water Equiv. 222.2″ /20.4” 279″ / 27.4″
Snowload in Valdez 78 lbs/sq. ft.

 

SNOWFALL at OTHER STATIONS:
LAST 24 HRS (2/17 AM)/STORM TOTAL (2/17)/STORM WATER EQUIV.:
Nicks Valley at 4200 ft (in): 2″ / 3″ / 0.3″
Upper Tsaina at 1750 ft (in): 2″ / 3″ / 0.3″
Sugarloaf at 550 ft (in): 6″/ 7″ / 0.6″
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