Avalanche Forecast

Cool temperatures followed by an increase in clouds and light snow showers Sunday afternoon will do little to change the avalanche danger. This is an unusual Moderate avalanche danger for the Pacific Northwest because it is not solely tied to a slow decrease in storm related avalanche concerns. Soft storm slab sitting over a spatially and elevation diverse persistent weak layer combined with a slick underlying old crust will be tricky to manage. 

For those near Stevens and Snoqualmie...pay extra attention near and below tree-line zone by looking for signs of shooting cracks and listening for whumpfing. These indicators of local instability even on low-angled terrain will clue you into instability that may extend into avalanche terrain.  

Moderate avalanche danger specifically means that natural avalanches have become unlikely...but human triggered slides are still very possible in specific areas and terrain features. 

Also, soft slabs that release down to the slick underlying crust, especially on steeper terrain, can make for a painful sliding surface. 

 

 

The tricky avalanche situation continues following our most recent storm cycle that began last Tuesday night with rising snow levels and rain for west slopes of the Cascades up to 5500 feet around Mt. Baker and above 6000 feet for the Olympics and near Crystal before transitioning to snow and colder temperatures. Snoqualmie and Stevens Pass saw some freezing rain before switching to snow with the onset of heavier precipitation Tuesday night.  A switch to westerly flow Wednesday morning at the passes allowed higher density snow to overload weaker lower density storm snow.  Natural avalanches were reported on late Wed and Thu by Stevens and Snoqualmie Pass DOT and professional ski patrol with releases down to a weak layer above the old and unusually slick crust formed during a prior dry spell.  Stevens Pass DOT classified the naturals as R2/D2.  Storm totals were highest at NWAC stations near the passes and Paradise with 18-36 inches while Mt. Baker and Crystal saw closer to 6-12 inches. Wind was less of a factor with this event with a more even distribution of storm snow and a general lack of wind slab.   

NWAC observers in Rainy, Stevens and Snoqualmie Passes continued to track surface hoar layers buried intact during this cycle with this layer showing signs of sensitivity with shooting cracks and whumpfing on Thursday and Friday. On Friday these layers were reported from the Source Lake area (Snoqualmie) the Yodelin area (Stevens Pass) in the below tree-line zones. These layers are most likely to be found below and near treeline on non-solar aspects in more open and less wind affected areas.  Alpental Pro patrol found that off the immediate valley floor...the storm slab still relatively soft and not particularly sensitive to ski cutting on Saturday.  

Surface hoar layer with thin rimed crust before it was buried near Stevens Pass 28 January, By NWAC Observers Jeff Ward and Dallas Glass.

Video made 1-30-14 near Stevens Pass of tests of the buried surface hoar layer: https://www.youtube.com/watch?v=IsYF79R6Rio

The Mt Baker ski patrol/NWAC observers reported numerous skier triggered storm slab avalanches of 6-12 inches on Shuksan Arm Friday and Saturday with the largest about 300 feet wide. Due to the relatively shallow and soft storm slab, there have luckily been no injuries or burials so far.  This is a different situation than the Cascade Passes.  Here the culprit surface hoar layer is sitting above the old slick crust and can be found on sheltered northerly aspects above the previous rain-line at 5500 feet.  Note: The forecast discussion is the same for Mt. Baker as for rest of the west slopes but the persistent slab concern aspect/elevation diagram is different. 

Regionally the avalanche danger is lower from Crystal Mtn and south, and also over to Hurricane Ridge in the Olympics. These areas received more rain before a transition to snow that made the likelihood of weak layer survival slim.  New snow has been reported as bonding well to the old surface by NWAC observers at Hurricane Ridge and Crystal Mtn pro patrol.  Also, no new avalanche activity has been reported in these areas. 

The mid and lower snowpack west of the crest consists mainly of crusts and melt form crystal layers which have generally not been reactive to to snow pit tests. Low snow amounts are limiting the avalanche danger on many south slopes and at low elevations due to terrain and vegetation anchors.