Avalanche Forecast
Regions: Mt Hood.
Cooling by Thursday will help to lower the wet snow avalanche problem. Glide and wet slab avalanches will be unlikely, but are difficult to predict and remain a threat while water drains following the heavy rains. Avoid travel on or below steep, unsupported terrain. Shallow fresh wind slabs are possible near ridges in higher terrain.
Detailed Forecast
Gradual cooling is underway as of Wednesday afternoon as a cooler trough approaches. Light to moderate showers at further lowering snow levels are expected Wednesday night and early Thursday with moderate crest level winds.
Cool air should be over the area by Thursday with only scattered light showers expected as high pressure rebuilds over the area.
This weather will allow the previously wet snow pack to begin re-freezing and strengthening, causing an overall decreasing trend in the avalanche danger.Â
We have already experienced a region-wide avalanche cycle, such that the overall likelihood of wet snow avalanches has diminished. However, destructive wet slab avalanches are still being reported in isolated areas in the Cascades as of Wednesday. Realize that wet snow avalanches, specifically wet slab avalanches, are very hard to predict and demand an extra amount of caution when engaging with avalanche terrain.
The cooling trend through Thursday will lower the overall danger as surface snow begins to form a crust and liquid water continues to drain. Â
With that said, there remains a possibility of further wet slab avalanches, especially on unsupported slopes with a rock face bed surface.  These types of avalanches are highly unpredictable and not necessarily tied to peak warming or rainfall. Besides their huge destructive potential, wet slab avalanches often surprise backcountry travelers when they run further than expected. Watch for evidence of large cracks forming in the snow due to glide, especially on terrain with rocky bed surfaces.
Cornices have been weakened and prone to failure due to rain and mild temperatures. Very large cornices have been reported in many areas and have been involved in recent accidents and close calls. A cornice failure could trigger a large and destructive wet slab avalanche.
If you manage to venture into the above treeline zone Thursday, expect new or previous wind slabs mainly on NW-SE aspects due to recent SW-W winds. Continue to watch for firmer wind transported snow on all aspects, especially in areas of complex terrain.
Snowpack Discussion
Weather and Snowpack
The first week or so of March was very cool and snowy. NWAC stations at Mt Hood piled up about 6-7 ft of snow.
A strong frontal system brought increasing precipitation and winds along with a warming trend to the Cascades on Thursday 3/9. On Thursday night rain pushed up to about 7000 feet at Mt Hood. By Friday morning NWAC stations at Mt Hood had about 1.60 inches of WE (water equivalent) but alas only rain to show for it. This gave the snowpack a huge test and caused an avalanche cycle at Mt Hood.
Moist W-SW flow and a stalled frontal boundary have produced periods of light to occasionally moderate rainfall on Mt. Hood Monday through Wednesday. Rainfall totals over the past three days on Mt Hood have ranged from about 2 to over 2.5 inches.
By Wednesday midday the snow line had lowered to about 6000 feet with fresh shallow wind slabs beginning to build on some lee slopes near ridges.
Recent Observations
NWAC observer Laura Green was out on Friday 3/9 and reported recent large cornice triggered slab avalanches in White River Canyon on SE aspects in the 6500-8500 ft range and in Heather Canyon on a NE aspect in the 6100-6800 ft range. Very large debris was also observed from avalanches in Newton Canyon.
Mt. Hood Meadows pro-patrol reported an increasingly saturated snowpack with increasing boot penetration from 5400' and down within their area early Monday morning.
No new natural avalanche activity was reported by the Meadows patrol through midday Tuesday.  The MHM patrol reported new snow beginning to accumulate above 6500 feet midday Wednesday.  Wet snow conditions persisted below treeline, but no recent avalanches were reported.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, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1
Wet Slabs
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slab avalanches can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty
A Wet Slab avalanche. In this avalanche, the meltwater pooled above a dusty layer of snow. Note all the smaller wet loose avalanches to either side.
Wet slabs occur when there is liquid water in the snowpack, and can release during the first few days of a warming period. Travel early in the day and avoiding avalanche paths when you see pinwheels, roller balls, loose wet avalanches, and during rain-on-snow events.
Elevations: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 2