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Avalanche Forecast

Archived

Mar 13th, 2017–Mar 14th, 2017

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

Regions

Olympics.

We have already experienced a region-wide avalanche cycle such that the overall likelihood of wet snow avalanches have diminished. However their destructive potential remains high. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain.  

Detailed Forecast

The relatively high snow levels will continue with rain forecast below 6000-7000 feet through Tuesday morning. We should see a relative break in the steady precipitation Tuesday afternoon before another wave of moisture returns Tuesday night. Periods of moderate W-SW winds above treeline will continue to transport new and recent snowfall only for the upper portion of the above treeline band Monday night through Tuesday. 

We have already experienced a region-wide avalanche cycle such that the overall likelihood of wet snow avalanches have diminished. However their destructive potential remains high. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain.

Loose wet avalanches are likely on steeper slopes with the additional rainfall. While most loose wet avalanches will be shallow, a few may gouge down to deeper layers and become more powerful than you expect. 

Cornices will be weakened and prone to failure due to rain and mild temperatures. Very large cornices have been reported in many areas and have been involved in recent accidents and close calls. A cornice failure could trigger a large and destructive wet slab avalanche. 

Wet slab avalanches are highly unpredictable and not necessarily tied to peak warming or rainfall. Glide cracks can indicate areas where wet slab avalanches are more likely to occur. Besides their destructive potential, wet slab avalanches often surprise backcountry travelers when they run further than expected. 

If you manage to venture into the above treeline zone Tuesday, expect new or previous wind slab mainly on NW-SE aspects due to recent SW-W winds. Continue to watch for firmer wind transported snow on all aspects especially in areas of complex terrain.

Snowpack Discussion

Weather and Snowpack

The first week or so of March was very cool and snowy. It looks like Hurricane had about 40-50 inches of snowfall.

A strong frontal system brought increasing precipitation and winds along with a warming trend to the Olympics and Cascades on Thursday. On Thursday night rain probably pushed up to about 5000 feet in the Olympics. By Friday morning Hurricane had about .5 inches of WE which looks like it fell as rain. This gave the snowpack a test and caused an avalanche cycle of several types of avalanches in the Olympics and Cascades.

Another front crossed the Olympics and Cascades on Saturday causing more SW-W winds, snow at higher elevations, and rain at low elevations. There was only up to a few inches new snow at Hurricane on Sunday morning.

A mild frontal system slowly sagged south across the Olympics and Cascades on Monday with moderate to locally heavy rainfall. Rainfall totals through 5 PM PST (or 6 PM PDT)

Recent Observations

Reports by NPS rangers early Sunday 3/5 and a report listed on the NWAC Observations page indicates there were at least three and possibly four separate triggered avalanches in the Hurricane Ridge area Saturday 3/4, including the areas known as Maggies, Hurricane Hill and Sunrise Face.

The Hurricane rangers report that a snow boarder triggered a cornice release on Friday which in turn triggered a very large slab avalanche on the locally named Pit Bull path on a NE slope at about 5000 ft. A loose wet avalanche near the summit of Mt Angeles in turn triggered a large slab avalanche on S-SE slopes at about 6000 ft. Other loose wet avalanches from S-SE slopes crossed the main road below the level of Hurricane Ridge.

Goat Creek avalanche where it crossed the road at about 3500 ft. Photo by Dave Turner.

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.

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.

Wet Slabs

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.