Avalanche Forecast

Archived

Jan 17th, 2018–Jan 18th, 2018

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

A storm overnight will bring strong winds and new snow. The storm will cause an increase in the avalanche danger overnight and Thursday. Expect dangerous avalanche conditions at mid and upper elevations. Choose conservative terrain and avoid slopes exposed to wind affected snow.

Detailed Forecast

An arriving storm overnight Wednesday will bring strong winds and snowfall. The storm should begin with rain at about the Hurricane ridge elevation, then transition to snow overnight and through Thursday with snowfall changing to showers Thursday with diminishing winds.

The incoming storm will build increasing wind and storm slabs over a thickening crust layer. The smooth crust layer may form a potential sliding layer, allowing any avalanche releases to run long distances as wind and storm slabs build.

Building wind and storm slabs should cause dangerous avalanche conditions near and above treeline by Thursday.

Monitor new snow and wind transport carefully and choose conservative terrain.

Snowpack Discussion

An incoming storm Wednesday evening is beginning to load the few inches of snowfall received Tuesday.

The underlying snowpack is dominated by a combination of strong crusts including a rain crust (formed Monday night) and melt-freeze crusts following the very warm temperatures this past weekend.

A foot of snow from last Thursday has now settled and is bonding to the previous recent rain crust. Below this rain crust, no notable layers of concern have been identified within the snowpack.

The height of snow across the terrain is quite variable with little snow in many areas below treeline. Numerous obstacles still exist at all elevations.

Observations

No recent observations have been received since the mild sunny weather last weekend.

NPS rangers reported a skier triggered avalanche from the Hurricane Ridge area Saturday morning. The avalanche occurred as the skier was traversing across a steep convex rollover locally known as Avalanche Run near Poma Bowl (SW aspect around 5300 feet). The avalanche was estimated to be 12 inches deep, about 100 feet wide, and ran down slope for 300-400 feet. The skier was caught and carried but did not sustain any injuries.

A separate natural, loose-wet avalanche occurred on Saturday in a known avalanche path named 20th of June. The avalanche occurred around 10am and ran for 300-400’.

Rangers also noted several glide cracks on steep smooth rock slabs.

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.