Avalanche Forecast

Light snow showers should end Tuesday night with further clearing expected through Wednesday with temperatures remaining very cold. 

The current Moderate avalanche danger in most areas is not solely tied to a slow decrease in storm related avalanche concerns as is more typical in this region.  Rather, 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.  Where the snow is less consolidated...generally small loose dry avalanches will be a concern on steeper slopes and near terrain traps. 

For those near Stevens and Snoqualmie...continue to 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. 

Only light amounts from 1-3 inches of additional very low density snow in showers has accumulated since the last significant storm tapered down Thursday. This has given about 5 days for the slow settlement process to work towards stabilization of several critical avalanche layers that have been identified since the storm.  This recent storm cycle 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 near Crystal before transitioning to snow and colder temperatures. Snoqualmie and Stevens Pass saw some light freezing rain before transitioning to snow with the onset of heavier precipitation Tuesday night.  A switch to warmer westerly winds Wednesday morning at the passes allowed for higher density snow or rain before the cooling trend set in.  Natural avalanches were reported on late Wed and Thu by Stevens and Snoqualmie Pass DOT and professional ski patrol as well as other observers 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, while a professional observer around Stevens Pass indicated many naturals had occurred releasing on the slick ice layer.  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. The Mt Baker ski patrol/NWAC observers reported numerous skier triggered storm slab avalanches of 10-12 inches on Shuksan Arm in the Mt Baker area Friday and Saturday with the largest about 300 feet wide. Due to the relatively shallow and soft storm slab, there were no injuries or burials.  Most of these storm slab weaknesses have now had several days to settle and begin stabilizing and thus should be less sensitive to trigger.  Wind was less of a factor during 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 mainly in the below tree-line zones. TAY reports from the Snoqualmie area Saturday also found this layer sandwiched between the rain crust and pre-storm crust.  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.  

Slick bed surface is visible after skier triggered soft slab avalanche on Shuskan Arm 2-1-14, Photo by Jeff Hambelton

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 10-12 inches on Shuksan Arm Friday and Saturday with the largest about 300 feet wide. Due to the relatively shallow and soft storm slab, there were no injuries or burials. 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.  This weak layer was not found on other nearby slopes of similar aspect and elevation in the Mt. Baker area showing a high degree of variability.  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. 

The most recent observations Tuesday from both Stevens Pass and Snoqualmie areas indicated that the weaknesses on or above the old hard crust layer have strengthened.  Several test profiles near Yodelin just east of Stevens Pass Tuesday revealed about 1 ft of fist powder over 1 ft of 4f settled powder that was fairly well bonded to the old hard crust layer.  No buried surface hoar was found in starting zone areas and was confined to mainly lower elevation areas.  ECT results varied from no propagation to hard result with partial failure.  In the Alpental backcountry reports Tuesday indicated that previous sensitive releases late last week were no longer reactive to ski tests.  While these layers are curing in the passes, further south near Crystal Mtn and Mt. Rainier 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 Crystal Mtn pro patrol. 

Future concerns: While significant stabilization has occurred, further settlement will be slowed by cold temperatures this week, helping to preserve some buried weak layers, slowing that snowpack stabilization process.  Increasing easterly winds towards mid-week should begin to transport weak surface snow near ridges and load some leeward westerly aspects. Reports of new surface hoar formed during the clearing Saturday night will have to be watched as the snow shifts around and is redistributed this week.  

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.