Avalanche Forecast

Stormy conditions Tuesday night should gradually ease by Wednesday as a brief break in storms occurs through the day Wednesday. Light winds and a lack of significant additional snowfall should allow for a gradual decrease in danger. However, cold temperatures will limit the stabilization Wednesday.

Storm slabs will continue to be sensitive to trigger and widespread Wednesday. The current storm slabs have formed over a variety of weak surface snow conditions, including near surface faceted snow, slightly settled powder or possible surface hoar. Natural or triggered storm slabs may also break down to deeper persistent layers, making larger and more dangerous avalanches possible Wednesday. Expect areas with the greatest storm snow totals to be most sensitive to this new load, mainly nearer to the crest. 

Where present, the persistent slab problem should remain sensitive to natural or triggered avalanches with the new snow load.

Fresh wind slabs should persist near and above treeline on a variety of lee slopes near ridges and exposed cross loaded features. 

The persistent slab problem still warrants attention throughout the Cascade range, especially in the Mission Ridge area where recent full depth avalanches have occurred. Recent significant loading will make this layer more sensitive to trigger where present. Remember that persistent weak layers are generally involved in larger avalanches and cautious route-finding and conservative decision making will be essential for safe travel.  Err on the side of caution by avoiding avalanche terrain of consequence, especially if you experience direct observations of this layer, such as whumpfing or shooting cracks. 

Weather and Snowpack

Strong storms a week ago Sunday and Monday deposited generally half to 1 inch of water equivalent along the east slopes through early Tuesday morning. Storm totals generally ranged from 6 - 12 inches along the east slopes during this cycle. Westerly winds were especially strong with the 2nd system late Monday night and into Tuesday with gusty winds mixing down into usually more wind sheltered terrain. 

A front Thursday and upper trough on Friday deposited about 1-5 inches of snow along the east slopes.  

Scattered snow showers, sunbreaks and generally light winds summed up the weather on Saturday with fair and cold weather seen on Christmas Day and early Monday, before a strong front arrived late Monday.

The strong front moved across the area early Tuesday, followed by snow showers and strong westerly winds through the day Tuesday at low snow levels. The most recent storm totals from Monday morning through Tuesday afternoon have been about 6-12 inches along the east slopes and still snowing in many areas Tuesday evening!

Recent Observations

NWAC pro-observer Jeff Ward was in the Icicle Creek area up to about 6300 feet on Wednesday and saw evidence of a widespread natural wind slab avalanche cycle during the last storm, with one very large crown seen on a north aspect. The December 17th persistent weak layer (PWL) was found at 15-30 cm below the surface on W to N to E slopes. The layer was unreactive both in large column snowpack tests, ski tests and cornice drops.

The NCMG on Friday and Saturday at Washington Pass had some planar hand shears in wind affected snow, but the only instability directly noted was small loose dry avalanches in steep rocky terrain. The 12/17 interface was found to be unreactive in several snowpack tests. 

NWAC observer Tom Curtis was on DirtyFace Peak near Lake Wenatchee Saturday and found the 12/17 PWL 15-25 cm down, but not propagating in snowpack tests on N-E-SE aspects between 4000-5500 feet. Tom also found shallow and stubborn wind slab in the near treeline band. 

A different story continues to evolve in the Mission Ridge area. On Wednesday avalanche mitigation produced 1.5 -3 ft hard slab avalanches in 3 separate paths! These avalanches were releasing on basal facets about 15 cm from the ground. On Thursday, snowpits on W-N-E slopes at 6500 feet continued to show hard slab layers giving hard compression test results with moderate quality shears on facets about 15 cm from the ground with about 120 cm (4 ft) of total snow. On Saturday, a backcountry ski tourer in the Lake Clara area near Mission Ridge reported a huge whumpfing noise, likely indicating a collapse of the basal facets. While no avalanche occurred, the terrain where the collapse occurred connected to a large avalanche path that was NE facing near treeline. While deep, persistent slabs in this area are unlikely to trigger, the appropriate travel response in consequential avalanche terrain is avoidance!. 

There have been no observations Tuesday following the new storm snow load, though given the sensitivity along the west slopes, similar conditions are expected with just somewhat shallower slabs.