Avalanche Forecast
Regions: Mt Hood.
Recent or new wind slab and recent storm slab may remain reactive on Thursday. The safest plan is to avoid avalanche terrain of consequence until we are sure these layers stabilize.
Detailed Forecast
West southwest flow aloft will carry the next front across the Northwest on Thursday afternoon and night. Winds should increase in most areas on Thursday but significant new snow during the daylight hours is expected mainly in the Olympics and northwest Cascades. A warming trend should also be seen with temperature inversions possible Thursday in the central west and southwest Cascades.
Further snow should be seen mainly in the Washington Cascades Thursday night with less or little at Mt Hood
Recent and renewed west to southwest winds mean wind slab will remain most likely on northwest to southeast aspects on Thursday. Wind slab may build further anywhere there is still snow available for wind transport in wind exposed areas.
Recent storm slab may linger in the near and below treeline at Mt Hood on Thursday. Storm slabs may be weakly bonded to the Solstice crust formed last week.
Snowpack Discussion
Weather and Snowpack
Strong storms around the Solstice deposited generally 3 inches of water equivalent recorded at NWAC stations on Mt Hood. Unfortunately, much of the heavy precipitation fell in liquid form with rain reaching above 7000 feet.
A system Thursday and Friday with low snow levels deposited about 5 inches of snow at NWAC stations on Mt Hood.Â
A strong front and strong west flow aloft was seen over the Olympics and Cascades on Monday and Tuesday. NWAC stations at Mt Hood had strong west winds and the station at Mt Hood Meadows had about 2.5 feet of new snow for the 48 hours ending Wednesday morning.
Recent Observations
Reports from the Mt Hood Meadows pro-patrol following the Solstice indicated a significantly different snowpack following rain, avalanches and cooling. A stout surface crust was found on all elevations up to at least 7200 feet. On exposed terrain, the crust was very supportable while in treed terrain the crust ranged from breakable to supportable.
The pro-patrol at Mt Hood Meadows patrol checked in early Sunday morning to report NW winds had scoured windward aspects near and above treeline exposing the thick crust on many aspects. The crust was slick enough that Santa had trouble landing his sled on any slope steeper than 20 degrees.
The pro-patrol at Mt Hood Meadows Tuesday reported very sensitive storm slab releases, with slabs releasing upon approach to ridges or steeper features.
The pro-patrol on Wednesday reported below treeline widespread sensitive 6-12 inch storm slab releasing by ski tests. Near tree line wind slab became reactive to 1-1.5 feet with good propagation. Above treeline explosives were used with larger hard deep wind slab releases where ski tests where considered too dangerous. The wind slab near and above treeline was seen mainly on E-SE slopes.
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, East, South East, 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.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1