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RegisterMar 29th, 2018–Mar 30th, 2018
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You may still trigger Loose Wet avalanches Friday on steep, rocky, and unsupported terrain where more than 6 inches of wet surface snow exists. If you see new roller balls, observe new Loose Wet avalanches, or experience wet surface snow deeper than your ankle, stay off of slopes greater than 35 degrees and minimize your exposure these slopes above you. If you travel in at higher elevations where dry snow can still be found, use visual clues such as cornices, snow drifts, and wind textured snow to identify and avoid steep wind loaded slopes.
You may still trigger loose wet avalanches Friday at elevations where moist to wet surface snow still exists. If you experience surface snow deeper than your ankle, see new rollerballs, or observe new loose wet avalanches stay off of nearby slopes greater than 35 degrees. You are most likely to encounter these conditions on steep, rocky, and unsupported slopes. In locations with a poor overnight refreeze, this may occur quickly with daytime warming. Rain showers and/or sun breaks during the day will also accelerate the development of wet surface snow.
Limit your exposure to steep rocky slopes above you if you see signs of wet avalanche conditions. Numerous natural wet avalanches occurred over the last several days traveling down and crossing common travel routes. Where and how you travel can minimize you and your team's exposure to this potential overhead hazard.
While not listed as a problem, we cannot rule out the potential for a wet slab avalanches. These avalanches can be difficult to assess and predict. Step back and avoid avalanche startzones if you see any new signs of slab avalanches in areas with wet snow.
Wind slabs continue to linger at higher elevations. If you travel in areas with dry surface snow expect wind slabs on slopes below cornices and near wind drifts. You are most likely to trigger an old wind slab on slopes greater than 35 degrees, on unsupported slopes, and below cornices. Use visual clues such as snow drifts, firm surface snow that cracks, and cornices to identify and avoid these steep wind loaded features.
Warm air temperatures and small sun breaks over the last several days created moist to wet surface snow in many locations. Generally two or more feet of melt-form snow exists at the snow surface. Wet surface snow resulted in a loose wet avalanche cycle in the Snoqualmie Pass area. This likely occurred in other locations as well.
At higher elevations drier soft snow can still be found. The elevation where this transition occurs can vary even with in a zone. Typically drier snow can be found above 6500 feet in the southern areas an near 5000 feet in the northern areas. Moderate winds formed wind slabs Monday through Wednesday near and above treeline. These wind slabs have been slowly gaining strength throughout the week.
Several avalanches 3/24-3/27 in the Crystal and Stevens areas failed on a layer of weak older snow buried on 3/22. Observations this week demonstrate this layer has been gaining strength. In some locations you may find a layer of small sugary facets above a firm melt-freeze crust. This layer has generally been reported 12-20” (30-50cm) below the snow surface.
The much older 2/13 facets layer just above the 2/8 melt-freeze layer can also still be found 4-6 feet (120-200cm) deep in the snowpack. While neither of these layers are listed in our current avalanche problem set, they may reawaken if they become wet.
Observations
North
On Wednesday Mt Baker Ski Patrol reported 8-12 inches (20-30cm) of soft snow over a recent melt-freeze crust. This snow was very rapidly effected by small sun breaks and thinning in the clouds. Winds earlier in the weak formed new wind slabs at higher elevations.
Central
On Thursday NWAC professional observer Jeremy Allyn traveled in the Snoqualmie Pass area. Jeremy reported numerous wet avalanche below and near treeline that over the last few days. He found moist to wet surface snow up to 4600 feet.
On Tuesday, Stevens Pass Pro-Patrol reported gusty west winds redistributing snow onto all aspects. Rain at Pass level in the afternoon caused small Wet Loose avalanches. A skier triggered avalanche was reported outside the ski area near Gemini Pass. This slab avalanche may have released down to the 3/22 crust.
South
On Wednesday. NWAC professional observer Ian Nicholson traveled in the Crystal backcountry. Ian found a 1" (2-3cm) surface crust on all aspects in the morning. This crust quickly broke down on sun exposed slopes as clouds thinned mid-day. Ian did observe the 3/22 interface and found that it was still reactive in some snowpack tests. This layer was 12-18" (30-45cm) below the snow surface.