Saturday through Tuesday December 20-23, 2014 Updated 8AM Dec 20
SATURDAY SUNDAY OUTLOOK FOR MONDAY & TUESDAY
DANGER TREND: The avalanche danger is Considerable. Since the last large storm Tuesday, Dec 16th, Thompson Pass has seen strong wind winds from varying directions. These winds moved a lot of snow and created slabs throughout our exposed terrain, especially near the Thompson Pass Gap where they were strongest (see activity below). After Saturday, the strong outflow northerly winds are forecast to decrease.
Wind Slab Avalanches – are likely on multiple aspects after onshore winds accompanying Tuesday Dec 16th’s storm, came from the SE, then switched to strong outflow winds dominated from the NE. This has led to many reported natural and skier triggered activity in our forecast area.
List of Avalanche Problems <here>
TRAVEL ADVISORY: Continually evaluate your terrain choices and the consequences of a slab avalanche, especially in steep terrain features. Look for trends in slab formation and be on the look out for recent avalanche activity, cracking, and whumphing.
-Dec 19 (seen Fri, but likely occurred during or just after the last storm: slightly blown in)
- Lower Python Face 3000-2000′: Large north-facing D2.5 natural slab avalanche: Crown 400-500 wide x 2 ft tall at steep convexity just above alder-line and ran 1000 ft to the flats below. Rocks and trees exposed in the crown face and bed surface.
- Cracked Ice-Python Drainage 3000-4000′: Two D1 and one D2 natural slab slides into the drainage. NE facing 1-2 ft crowns at steep convexity just below ridge line, wind loaded from the South.
- Catchers Mitt 4000′: A couple large, natural, slab avalanches were faintly seen through the clouds down the NE ridge toward Worthington.
- Moonlight Basin 3200′: Small skier released winds slab pockets on rollovers; localized shooting cracks; few settlements lower down
- MP 54 – Continental: Numerous large whumphing (snow settlement) below treeline.
- Gap at Thompson Pass: one size 2 slab release
- Wilbur’s at Milepost 40: one size 2.5-3 reached the valley floor
- Rice Mountain, MP 54: Size 2.5 avalanches with 3 ft crown (ran from ridge to brushline)
- Numerous point release storm snow avalanches to size 2 released off steep features
Avalanche sizing using the destructive scale <here>
Avalanche size estimation aid <here>.
SNOWPACK DISCUSSION: Strong winds from the SE, then reversing to the NE, have extensively moved around the 2 feet of new snow that has fallen in the last week. Many people have seen the resulting slab activity this has produced in our area. Luckily, time allows these new slabs to stick and bond to the surrounding snow. As these new upper layers strengthen, still keep an eye out for unsupported slabs in steep terrain features.
Deeper in the snowpack is a more interesting variety of weaknesses. Two melt freeze crusts seem the be the biggest problems with facets above and below. For the most part, these layers seem less sensitive than previously; requiring more force than before to initiate failure. Something observed Friday was that there is a slight difference in results depending on where one is in the region. Closer to Thompson Pass which sees warmer temperatures, the facets (sugar snow) above the crusts tend to be the weak points (ECTP 21, 22 RP), with strong pencil hard facets near the ground. On the other hand, when further inland, where it’s colder, the upper facets are not as sensitive and failure is directed down below the crusts to fist hard facets near the ground (ECTP 24 BRK).
WEATHER: Strong northerly winds Saturday with increasing cloud cover. Sunday looks like scattered snow (slight chance of rain in town if temps edge above freezing) that will increase in the afternoon and into Monday, before dying out early Tuesday morning. A total of 6 inches of new snow could accumulate by Tuesday.
Use links below to follow the up and coming weather.
|SNOW & PRECIPITATION HISTORY:||
|Updated||12/20 AM||12/18 AM|
|Current Snow Depth||5.0″||
|24 Hour Snow / Water Equiv.||0″ / 0″||0″ / 0″|
|December Snow / Water Equiv.||22″ / 1.9″||52″ / 5.1″|
Total Winter Snowfall / Water Equiv.
|27″ / 1.00″||121″ / 13.1″|
|Snowload in Valdez||7.7 lbs / square foot|
|Snow Depths and Water Equivalents:||date||depth||snow water equivalent|
|Valdez Ball Fields (Wood Way)||12/10||6||1.1|
|Worthington Glacier air strip||12/8||32”||5.3”|
|Milepost 37 Tsaina River bridge||12/8||24”||4.4”|
- NWS forecast for Northeast Prince William Sound <here>
- NOAA NWS spot forecast for Thompson Pass <here>
- Valdez Glacier UAF weather station at 6600 feet <data here> <map here>.
- Thompson Pass weather <here>.
- Further weather resources <here>
Our region is “one of the snowiest places on earth” says the recent weather detective climatologist investigation into the Serendipity / Rendezvous snowfall record set in 1963 <here>.
SNOW CLIMATE ZONES:
- Maritime (Coastal) – from the Port of Valdez to Thompson Pass, all waters flowing into Valdez Arm and everything south of Marshall Pass.
- Inter-mountain (Transitional) – between Thompson Pass and Rendezvous Lodge.
- Continental (Interior) – the dry north side of the Chugach (north of 46 Mile, including the Tonsina River).
- Upper Elevations: Alpine – Above 2,000 feet
- Mid Elevations: Treeline – 2,000 feet
- Lower Elevations: Below treeline – Below 2,000 feet
Learn about recognizing avalanche terrain and decision making in the Avalanche class Level 1 January 9-11, 2015.
Develop snow analysis skills at the Avalanche Level 2 March 6-9, 2015.
Free smart phone avalanche forecasts at: http://www.
Like warm milk, this forecast expires after 24 hours