Avalanche Forecast

Generally decreasing light to occasionally moderate snow showers at further cooling temperatures along with diminishing winds are expected Thursday.   The cool temperatures should preserve any existing weak layers within storm snow as well as layers such as buried surface hoar or weak bonding between old and new snow. 

Future avalanche concerns:  Buried surface hoar will most likely be preserved near the Cascade passes due to a light freezing rain crust formed Tuesday and at higher sheltered elevations near the Cascade crest that did not see rain. This avalanche concern should not be widespread throughout the Olympics and Cascade west slopes but will present challenging terrain management for backcountry travelers moving forward in the week as additional loading stresses this recently buried weak layer. Look for shooting cracks and listen for whumpfing even in low angle terrain as a clear sign that this persistent weak layer exists and may extend into avalanche terrain.

A two week spell of mild and dry weather was officially broken as a strong front finally moved across the area early Wednesday.  The dry stretch produced strong temperature inversions, periods of moderate cool easterly flow in the passes and warm sunshine at higher elevations.  The main avalanche activity over this period was limited to generally small natural wet-loose slides confined to steeper slopes, especially near rocky terrain. 

Snow surfaces across the region were highly variable prior to the latest storms arrival, typified by firm conditions at low and mid elevations with a smooth rain or melt freeze crust on many non-solar aspects (the source of many sliding accidents over the weekend), breakable crusts in the trees, rougher melt-freeze crusts on exposed solar aspects and wind affected snow on higher lee slopes. A generally favorable mid and lower snowpack of crust layers and melt form crystals should still be an appropriate regional description (see photo below). The low snow amounts on many south slopes and at lower elevations and ample terrain and vegetation anchors remain a factor to reduce the overall danger in those areas.  

Of more important note is the extensive surface hoar growth that has been reported during the last week with generally shallow growth at Cascade pass levels but reaching into the above tree-line zone and with significant growth in the more sheltered areas near the Cascade crest up to 20-30 mm thick!   NWAC observers in the Rainy Pass area below treeline on Tuesday reported a light rimed crust capping nearly 30mm of surface hoar and preserving this layer for additional loading (see photo and video below). Shallower surface hoar was found as they travelled to near 5500 ft.  WSDOT avalanche professionals at Stevens Pass reported a shallower and less worrisome layer of surface hoar affected by moderate east winds. 

NWAC observers video 1-28-14 from Rainy Pass: https://www.youtube.com/watch?v=7Kh_nvcDxxs

Surface hoar with thin rimed crust near Rainy Pass @ 4600 ft 1-28-14, Photo by Jeff Ward and Dallas Glass

Test pit profile shows stable mix of crusts and moist 1F snow in the upper and mid snowpack on a SW Aspect @ 5000 ft near Artist Point, Mt. Baker, Photo by Jeff Hambelton 1-27-14.

Open crevasse on Silverstar Glacier in North Cascades, Photo by Jeff Ward 1-23-14

The current storm has deposited varying amounts of new snow ranging from a few inches in the north, to near or over 1 foot in many areas.  The new storm snow has fallen at cooling temperatures and began as either wet heavy snow or rain in many areas with a cooling trend.  The cooling trend likely formed good bonding to the old snow surface.  Strong crest level winds have likely built some wind slab on lee slopes, mainly NE through SE facing slopes.  

However a different upper snow structure may exist near the crest and Cascade passes where some areas may have an underlying slick crust preventing good bonding with new snow.

See Stevens and Snoqualmie pass area zone forecast for details in the passes.