Avalanche Forecast
Regions: Mt Hood.
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.
The heavy snowfall snowfall intensities received late Tuesday will likely produce layers that require time to stabilize.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.
Although they will not be listed as avalanche problems, loose dry avalanches are possible Wednesday, particularly on steep slopes. Watch for potential loose wet avalanches on steep, solar slopes if there are significant sun breaks.
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.
Remember that closed ski areas without avalanche mitigation are equivalent to backcountry terrain! Â
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 at many NWAC stations including Mt. Hood.
A front and a splitting upper trough crossed the US west coast Sunday and Sunday night. At Mt. Hood Meadows, the passage of the sharp cold front on Sunday caused W winds in the 30-40 mph range to decrease to decrease to the 10 mph range. Temperatures dropped from 40's into the 20's at NWAC stations in the Mt. Hood zone. New snow amounts were fairly light ending Monday morning, ranging from 1-3".Â
Lingering light snow showers were seen on Monday at continued cooler temperatures and lighter winds, with 2-3" of lower density snow at Mt. Hood stations.
On Tuesday, a front brought a brief bump in snow levels to about 5000 feet, with SW to W winds in the 10 mph range with gusts in the 20's. By Wednesday morning, 24 hour snow totals are expected to be in the 10-12" range and 48 hour totals in the 10-15" range at Mt. Hood.
Observations
No recent observations from Mt. Hood.Â
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: Likely
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: Likely
Expected Size: 1 - 1