Avalanche Forecast
Regions: Mt Hood.
A lot is going to start happening on Thursday and regional timing of weather and avalanche conditions will be tricky. But it is pretty certain that wind, snowfall and a warming trend will arrive first at Mt Hood on Thursday.
Detailed Forecast
A lot is going to start happening on Thursday and regional timing of weather and avalanche conditions will be tricky.
South to southeast winds at Mt Hood should continue to increase Wednesday night in advance of an incoming front.
The front with increasing snow and a slight warming trend should begin to lift south to north over the Northwest starting in the south at Mt Hood on Thursday.
Watch for wind transport and new wind slab mainly on southwest to northeast aspects at Mt Hood on Thursday. But check for firmer wind transported snow on all aspects since confidence is not high on which aspects to highlight. The slight warming trend should enhance the formation of new wind slab on Thursday.
New storm slab also seems likely by the end of the day on Thursday in areas that rapidly accumulate snow. The slight warming trend should also enhance the formation of new storm slab on Thursday.
With deep unconsolidated snow in most areas, there is an increased risk for tree well and snow immersion suffocation at this time. Ride or ski with a partner and keep them in sight at all times!
Even though the lower part of the below treeline band is filling in, watch for early season travel hazards such as barely covered rocks and open creeks.
Further new wind and storm slab likely Thursday night. The warming trend should continue to enhance the formation of these layers.
Snowpack Discussion
Weather and Snowpack
Active snowy weather has been seen so far in December. NWAC stations at Mt Hood had about 2-4 feet of snow so far in December through Tuesday morning with an overall cooling trend.
Cold fair weather has been seen the past couple days. There have been many reports of right side up, favorable density profiles with lower density snow nearer the surface. We've been hearing the term "as good as it gets" quite a lot lately!
Given the favorable snowpack profile, good bonds of older snow layers and a lack of deeper layers of concern, avalanche problems should be confined to the most recent storm snow at this time.
Cold fair weather like this usually causes some new surface hoar layer and near surface faceted snow. This snow can make for great skiing or riding. But these layers will need to be watched if loaded by wind transported snow or new snow.
Recent Observations
The pro-patrol at Mt Hood Meadows Sunday indicated a favorable snowpack profile with very limited slab like character noted, except for isolated features were wind deposited snow produced some very soft slab releases of little consequence.
By Monday and Tuesday the pro-patrol at Mt Hood Meadows reported only isolated wind slabs in exposed terrain at the upper elevations. These avalanches were fairly shallow within the upper 4-8 inches of snow mostly and released with explosives only. In general, most areas have surface snow conditions lacking slab character with low cohesion snow providing some excellent conditions.
Lastly the indefatigable pro-patrol at Mt Hood Meadows on Wednesday reported light winds that were not causing wind transport. The upper snowpack remains generally right side up with good skiing and riding conditions. Some surface hoar was seen in sheltered locations.
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Avalanche Problems
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, South West, West, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1
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