Avalanche Forecast
Regions: Mt Hood.
Large and dangerous wind slabs should be less likely to trigger Wednesday but wind loaded slopes should be avoided for at least one more day especially above treeline. Small loose wet avalanches are possible on steep solar slopes below treeline with daytime warming.
Detailed Forecast
Storm slabs should have settled out by Wednesday, shifting the focus to lingering wind slab mainly found above treeline and the potential for small loose wet avalanches on steep solar slopes below treeline.Â
Large and dangerous wind slabs should be less likely to trigger Wednesday but wind loaded slopes should be avoided for at least one more day especially above treeline. Small loose wet avalanches are possible on steep solar slopes below treeline with daytime warming.  Â
Snowpack Discussion
Weather and Snowpack
Clear and cold weather from Wednesday, December 14th to Friday, December 17th allowed widespread surface hoar and near surface faceted snow to develop in the Cascades and Mt. Hood. Thin sun crusts formed on steeper solar slopes during sunny periods.
However, persistent weak layers likely have not survived in the Mt. Hood zone due to the copious water amounts received over this latest storm cycle. Strong westerly flow directed two Pacific frontal systems into the PNW Sunday night and again Monday night with generally 3Â inches of water accumulating at Mt. Hood NWAC stations through early Tuesday morning.
Unfortunately, much of the heavy precipitation fell in liquid form with rain likely reaching up to about 7000 feet late Monday night and Tuesday morning.Â
 A sharp cooling trend followed mid-day Tuesday with about 2 inches of snow in post-frontal showers.  A strengthening rain crust was noted near and below treeline by late in the day Tuesday with the arrival of colder air. Â
Westerly winds were especially strong with the 2nd system late Monday night and into Tuesday with gusty winds mixing down into usually more wind sheltered terrain.Â
Recent Observations
NWAC pro-observer Laura Green was out in the Newton and Clark drainages on Friday a found a mix of surface conditions of recent snow and 3-4 mm surface hoar with a thin sun crust on solar slopes. The upper snow pack on N-NE slopes was right side up with no direct signs of instability.
The Mt Hood Meadows pro-patrol on Sunday reports fairly widespread surface hoar and near surface faceted snow up to about 7300 feet. Calm winds have allowed it to develop or grow the past couple days.
Avalanche control observations were limited Tuesday morning and the below treeline snowpack appeared to be handling the heavy rain remarkably well with little natural or human avalanche activity observed. However, by late Tuesday afternoon and after some partial clearing, debris from a very large wind slab avalanche was observed above treeline on a ENE aspect at 7500 feet in the Mt. Hood Meadows ski area. This R4.5 - D3 avalanche likely occurred Monday night and cleared out two start zones running roughly 1500 feet vertical. From a distance, the crown was estimated to be several feet thick!Â
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, South.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2
Loose Wet
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1