Avalanche Forecast
Regions: Olympics.
Watch for recently formed storm and wind slab layers, especially if you venture to higher elevations. Don't overlook early season terrain hazards, such as poorly covered rocks or vegetation and creeks, particularly at lower elevations.
Detailed Forecast
On Wednesday, a shortwave ridge moves across the Pacific Northwest with a temporary decrease in winds and precipitation. This weather should generally allow new or recent storm and wind slab layers to begin stabilizing.
Watch for storm slabs in areas that received more than a few hours of moderate or heavy snowfall intensities.Â
Watch for firmer wind-transported snow on lee slopes near ridges, generally northwest through southeast aspects, but watch for it on other aspects in areas of more complex terrain.
Storm or wind slab avalanches may entrain recent snow down to the firmer refreezing snow from last week.
Although they will not be listed as avalanche problems, loose dry avalanches are possible Wednesday, particularly on steep slopes.Â
Watch for the numerous travel hazards such as open creeks, barely buried rocks and trees, creating poor and challenging travel conditions, especially below treeline.Â
The avalanche danger should generally decrease for all elevation bands on Wednesday.
Snowpack Discussion
The great start to the 2017/18 PNW Winter took a giant step backwards last week. Warm, wet weather caused wet snow and glide avalanches and snowpack consolidation with total snow depths decreasing by 50% or more from their mid-November peak depths.
A front and a splitting upper trough crossed the US west coast Sunday and Sunday night. At Hurricane Ridge, the passage of a sharp cold front on Sunday caused south winds in the 20's with gusts to the 40's before changing to westerly in the 10-20 mph range. Temperatures generally dropped from the 40's into the 20's on Sunday afternoon. New snow at Hurricane Ridge was 5" on Monday morning.Â
There was some partial clearing at Hurricane Ridge on Monday.Â
On Tuesday, a front brought a brief bump in snow levels with the temperature climbing to about 31 degrees at Hurricane Ridge. Winds were generally south in the 10's with gusts in the 30's. By Wednesday morning 24 hour snow totals are expected to be about 5" and the 48 hour total should be about 10".
Observations
NWAC pro-observer Matt Schonwald was out in the Hurricane Ridge area on Saturday. Matt found pockets of wind slab up to 15 cm (6") thick on north aspects of Mt. Angeles near 5000 feet. Wind slabs were stubborn to trigger and did not propagate.  A few glide cracks were visible in the Hurricane Ridge area, but the only large slide observed from the recent rain events was noted off the south side of Mt. Angeles. Windward slopes above treeline were largely stripped of snow.  Â
The ranger at Hurricane Ridge on Monday morning reported no avalanche activity.
Avalanche Problems
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Wind Slabs
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.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features. They can be avoided by sticking to sheltered or wind-scoured areas..
Wind Slab avalanche. Winds blew from left to right. The area above the ridge has been scoured, and the snow drifted into a wind slab on the slope below.
Wind slabs can take up to a week to stabilize. They are confined to lee and cross-loaded terrain features and can be avoided by sticking to sheltered or wind scoured areas.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1