Avalanche Forecast
Regions: Mt Hood.
The stability of the Cascades snowpack has greatly increased after avalanche cycles and consolidation the past week. You should mainly need to watch for previous slab at higher elevations and the development of loose wet avalanches at lower elevations on Friday.
Detailed Forecast
A low pressure system is expected to form well to the SW of track towards the central Washington coast on Friday, before moving inland Friday night. This system should spread increasing light precipitation to Mt Hood Friday morning, before spreading to the remainder of the forecast area Friday afternoon, with rising snow levels. The peak in winds, snow levels and precipitation are expected Friday night into early Saturday morning.
At Mt Hood previous wind slab is most likely to linger on NW to SE aspects due to previous SW-W winds. But watch for firmer wind transported snow on other aspects especially in areas of complex terrain.
Small loose wet avalanche conditions are most likely to linger at lower elevations or to develop as rain moves in on Friday afternoon. Watch for surface wet snow deeper than a few inches, rollerballs or increasing small natural releases.
Although the likelihood of wet slab or glide avalanches has greatly decreased, continue to avoid unsupported slopes where you know there is a smooth underlying surface, or slopes with glide cracks.
It is always a good plan to avoid areas on ridge where a cornice maybe present and slopes below cornices.
Remember to re-evaluate plans if weather conditions are different or deteriorate sooner than expected.
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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, winds and warming 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 test and caused an avalanche cycle at Mt Hood.
Moist W-SW flow and a stalled frontal boundary produced periods of light to occasionally moderate rainfall on Mt. Hood Monday through Wednesday. Rainfall totals over the three days on Mt Hood ranged from about 2 to over 2.5 inches. About 1.5 ft of snowpack consolidation was seen the past week at Mt Hood.
Cooling and a little snow was seen on Wednesday night. NWAC stations at Mt Hood had 2-3Â inches by Thursday morning.
The past week of weather has done a reset of the snowpack in the Cascades. Most areas at the end of Thursday are light amounts of new snow over a firm, consolidated, stabilized snowpack.
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.
The MHM patrol reported an increasingly saturated snowpack with increasing boot penetration from 5400' and down within their area early Monday 3/13.
The MHM patrol reported new snow beginning to accumulate above 6500 feet midday Wednesday.  Wet snow conditions persisted below treeline with no recent avalanches.
By Thursday at 6600 ft the MHM reported 4-8 inches of recent snow over deep wet consolidated snow. Laura Green also reported a cornice caused a small slab in the lower White River Canyon.
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.
Likelihood: Possible
Expected Size: 1 - 1
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: Treeline, Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1