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Avalanche Forecast

Archived

Mar 5th, 2016–Mar 6th, 2016

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Wet snow conditions will prevail below treeline with a transition to shallow storm hazards above treeline. Avoid steeper slopes where even a small loose wet avalanche could entrain significant amounts of recent snow or where you could be flushed into a terrain trap. Be wary of unstable layers created during heavier showers that would make shallow wind or storm slabs found at higher elevations more likely to trigger.

Detailed Forecast

Light to locally moderate rain Saturday night will transition to showers early Sunday morning with a slow cooling trend during the day. Showers may occasionally be intense on Sunday forming unstable storm layers.   

The avalanche danger will temporarily rise Saturday night during periods of peak rainfall. On Sunday, wet snow conditions will prevail below treeline with a transition to shallow storm hazards above treeline. Avoid steeper slopes where even a small loose wet avalanche could entrain significant amounts of recent snow or where you could be flushed into a terrain trap. Be wary of unstable layers created during heavier showers that would make shallow wind or storm slabs found at higher elevations more likely to trigger.

Cornices formed over the last week should still be weakened by the mild temperatures so be aware of the overhead hazard. 

Non-avalanche hazard: Despite our seasonally, healthy snowpack, many creeks are open and difficult to cross due to the periodic warm temperatures and rain events.  

Snowpack Discussion

Weather and Snowpack

The last significant snowfall in the Olympics occurred Sunday, 2/28 through early Monday when about 12 inches of snow accumulated at Hurricane Ridge accompanied by a cooling trend. 

Fluctuating freezing levels and periods of rain or snow Tuesday through Friday have maintained about the same total snow depth at Hurricane Ridge with a few inches of new snow received each day. There have been periods of strong, mostly southerly, winds during frontal passages each day this week. With the mild temperatures this week, storm related instabilities have most likely been quick to settle out. For perspective, the averaged freezing level measured in March thus far has been 5700 ft at Forks. 

Moderate rain fell Tuesday, 3/1 with rain reaching to about the near treeline band or at least 6000 feet.  Another front Thursday deposited about 4-6 inches of new snow at Hurricane Ridge by Friday morning, however warmer temperatures and increasing precipitation began to settle this snow by afternoon.

On Saturday morning, the NPS Olympic rangers reported 6 inches at the Hurricane Ridge snow stake. 

The mid and lower snow pack along the west slopes should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Note: The NWAC weather station at Hurricane Ridge is temporarily down due to communication issues and we hope to have it restored next week. 

Recent Observations

NPS rangers indicated widespread wind-affected snow in the Hurricane Ridge area with powdery snow in non-wind affected terrain Saturday morning. Cornices had grown fairly large and were sensitive to triggering. 

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.