Avalanche Forecast

The main concern Saturday should be areas of shallow wet snow developing on sun exposed slopes, especially below rock outcrops or cliff areas.  Continue to be aware of potential deeper weak layers such as the weaknesses noted near buried crusts.  While any avalanche on these layers should be very hard for a person to trigger, a snowmobile or falling cornice may add the load necessary so more caution and analysis may be required before committing to a steep lee or northerly slopes.

Freezing levels and temperatures should remain warm Saturday with weakening winds.  Mid and higher terrain away from the lower Cascade crest or passes will have better chances of small wet loose avalanches.  Avoid steep solar aspects or gullies in the sun if you see surface snow there deeper than a few inches or natural wet loose avalanches.

 

 

The last week long storm cycle to impact the Northwest ended about the 14th of January.  The storm dropped 2-4 feet of snow at most NWAC sites near and west of the crest with somewhat lesser amounts near Hurricane Ridge. A widespread natural avalanche cycle occurred towards the end of these storms producing many slab releases ranging mostly from size D2 to D3.  

Over the past 11 days, clear weather and warm temperatures have helped to maintain a variety of surface snow conditions.  Varying amounts of low clouds and temperature inversions kept lower elevations cooler with many strong surface crusts noted, both near surface as well as throughout the mid and upper snowpack. 

The warm days and cooler nights lately have been producing generally stable surface crusts on solar aspects at all elevations until mid-day softening occurs, and on most other aspects up to mid-mountain where a rain crust exists. A generally favorable mid and lower snowpack of crust layers and melt form crystals exists throughout the west slopes. The avalanche danger is low at lower elevations where there is little snow and and ample terrain and vegetation anchors. There is little snow cover on solar aspects even into the near tree-line zone near Hurricane Ridge. (see photo below). 

Avalanche activity has been little to none during this dry and mild period with only a few small triggered loose-wet slides noted on some steeper sun exposed slopes. 

Recent layers of concern: On northerly or shaded aspects near and above treeline not affected by the warm temperatures or weak January sun small areas of surviving slab layers may still be found. Strong radiational cooling at night has increased temperature gradients and faceting in the upper snowpack.  NWAC observers at Hurricane and Nason Ridge (near Stevens Pass) the past several days are reporting moderate or hard compression, extended column and deep tap test results with sudden collapse or sudden planar fracture characteristics. (see photos below) These results are found in the upper snow pack, as far down as 65 cm near Nason Ridge, releasing due to crusts and thin faceted snow layers. Due to the moderate and hard results, weak layers, would likely require larger triggers, perhaps a cornice or a snow mobile.  While there have been no known avalanches on any of these layers we will continue to monitor their characteristics as heavy future loading may likely be required to activate these weak layers.  They also have not been widely found throughout the region so they may be more isolated rather than widespread.  The upper snowpack is becoming more spatially variable during this ongoing dry spell.  Widespread reports of surface hoar growth has been reported this week but will have to withstand additional sunshine, warm temperatures and winds to become an issue when we finally receive more precipitation. 

Deep Tap Test - DT13 SC Q1 at 67 cm due to crust and facet layers,

Nason Ridge. NWAC observer Tom Curtis, 20 January.

ECTP29 SC Q1 at 67 cm due to crust and facet layers,

Nason Ridge. NWAC observer Tom Curtis, 20 January.

Faceted crystals from the upper snow pack, Klahhane Ridge near Hurricane Ridge, NWAC observer Katy Reid, 20 January.

South slopes Klahhane Ridge, Olympics - still awaiting winter! NWAC observer Katy Reid, 18 January.

Report of the cornice/avalanche fatality on Lewis Peak available at https://www.nwac.us/accidents/accident-reports/ 

Local non-avalanche hazards:  On 13 January a heavy local freezing rain event occurred in the Snoqualmie Pass area above about 4500 feet, covering the surface with about a 2-3 inch ice crust.  This crust should break down over time but a fall on a slope on this surface could result in a long and dangerous ride!  Additionally, guides in the North Cascades have noted some thin bridging over several crevasses on lower glaciers.  During this shallow snow season, any thin and potentially weak bridges over crevasses may present an additional danger for those travelling on glaciated terrain.