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Avalanche Forecast

Archived

Mar 12th, 2017–Mar 13th, 2017

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

Regions

Olympics.

Mother Nature is throwing a lot of avalanche problems at us right now so review the forecast to remind yourself of what to watch for if you are planning a trip into the backcountry on Sunday. Re-evaluate or ratchet back your plans if you encounter significantly more new snow than described at higher elevations.

Detailed Forecast

A short break between frontal systems should be seen Sunday. Light showers mainly over the Cascade west slopes should taper off in the morning. Renewed light rain or snow should be seen mainly over the Olympics and northwest to central west Cascades as moisture from the warm front of the next system reaches the Northwest. Re-evaulate your plans if the weather is not turning out as expected.

Mother Nature is throwing a lot of avalanche problems at us right now so review the forecast to remind yourself of what to watch for if you are planning a trip into the backcountry.

New or previous wind slab should be suspected mainly on NW-SE aspects above treeline due to recent SW-W winds. But watch for firmer wind transported snow on all aspects especially in areas of complex terrain.

New sensitive storm slab is most likely above treeline in areas that receive more than a few inches of rapidly accumulating snowfall.

Avoid travel on ridges near where cornices will have been loaded and weakened by recent storms and avoid steep slopes below cornices that may fail at any time. Cornices have been reported as large and sensitive in several areas and have been involved in recent accidents and close calls.

Loose wet avalanches are most likely on solar slopes in the near and below treeline especially if you are in an area with sunshine or little cloud cover. Watch for surface wet snow deeper than a few inches, pinwheels and initial small releases that will get bigger the longer the sun heats the snowpack.

Dangerous avalanche conditions are expected Sunday. We only got a taste of the spring stabilizing process the past couple days. Avalanches may step down or entrain deeper layers and be large and dangerous especially if they reach the Valentine's Day crust layer.

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 huge 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. It looks like there is only some light amounts of new snow at Hurricane on Sunday morning.

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

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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.