Avalanche Forecast
Regions: Mt Hood.
The avalanche danger will be decreasing on Wednesday. But the rate of this decrease is less certain so you will need assess conditions and be able to make wise terrain choices if you are out on Wednesday.
Detailed Forecast
Snow showers should gradually end and strong west to northwest winds should gradually decrease on Wednesday at Mt Hood with much cooler temperatures.
Unlike the Washington Cascades the avalanche danger may not significantly decrease until later Wednesday at Mt Hood. There will be a greater need assess conditions for yourself if you are out on Wednesday.
Storm slab will linger on Wednesday in areas that had at least several hours of rapidly accumulating snowfall and that developed weak storm layers on Tuesday.
Given the strong winds, small to large wind slabs are still likely near and above treeline, mainly on NW through SE aspects near ridges, but are possible on other aspects. Avoid ridges or terrain features with firmer wind transported snow.
The recent warm weather has melted much of the early season snowpack. Expect terrain hazards with poorly covered rocks, vegetation and creeks, particularly on south-facing terrain at lower elevations, and on exposed ridges where wind events have stripped much of the seasons snowcover.
Snowpack Discussion
Fair weather dominated the first half of December and a number on the early season snowpack at Mt Hood, gradually consolidating snow and returning many areas to very shallow early season conditions. The most consistent snowpack remains on shaded northerly aspects in the upper below treeline to near treeline.
West flow began to carry a series of fronts across the Northwest starting about December 16th.Â
The last front in the series is crossing the Northwest on Tuesday. Storm snowfall totals Wednesday morning at Mt Hood should end up in the 1-2 foot range. Very strong west to southwest alpine winds Tuesday will probably continue into Wednesday morning at Mt Hood. Temperatures rose a bit to the upper 20's or near freezing Tuesday depending on elevation and will begin cooling on Tuesday night
Observations
The Meadows pro patrol on Tuesday reported new wind slab forming near tree line and did not need to venture to the above tree line. New snow was bonding well to previous surface below tree line.
NWAC pro oberserver Laura Green was in the Heather/Mitchell drainages on Tuesday in low visibility conditions, her test results indicated several storm layers in about 1 foot of new snow but with low quality results. Total snow depths were quite varied and the new snow was bonding well to previous melt freeze snow.
On Monday the Meadows pro patrol reported a major freezing rain event with up to 6-8 inches of ice in the 6000-7300 foot elevation range, with rain softened snow at lower elevations.
Ice coated tree limbs at Mt Hood Meadows on Monday December 18th. Photo Nick Burks.
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: All elevations.
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