Avalanche Forecast
Regions: Mt Hood.
The overall snowpack is strong and well consolidated with a variety of surface conditions, but is lacking depth and coverage in some areas. Heads up when snow returns on Friday in case new snow buries surface hoar or near-surface facets on non-solar slopes or in terrain below the ongoing inversion.
Detailed Forecast
This stretch of high pressure has featured mostly sunny and warm conditions with light winds for areas west of the Cascade crest and at higher elevations. Local colder and cloudier conditions have been seen at lower elevations exposed to easterly flow. More of the same can be expected on Thursday.
Loose wet avalanches are unlikely, but might be encountered in isolated steep solar exposed slopes below rocks or trees absorbing more radiation. Â
This weather provides a nice opportunity to check out a variety of surface snow conditions but be sure to watch for early season/low snow travel hazards. Early season terrain hazards include poorly covered rocks, vegetation and creeks, particularly at lower elevations.
Heads up when a variety of weather conditions is likely on Friday. Snow may bury surface hoar or near-surface facets in some areas. Freezing rain may cap these layers mainly at low elevations in the passes or deep valleys. As you make your weekend plans, keep an eye on the weather forecasts.
Snowpack Discussion
Strong high pressure has now been over the region for over a full week. Sunshine and very mild temperatures have been the story with cooler temperatures and areas of low clouds at lower elevations. This weather has allowed for overall strengthening and consolidation of an already strong snowpack. Total snow consolidation in the Mt. Hood area ranges from 5-8" since December 3rd, with settled old storm snow of about 1 to 1.5 feet over the strong Thanksgiving rain crust at Mt. Hood.
Some natural small loose wet slides have occurred on mainly steep sun exposed slopes over the last week, but have become much less frequent over the past several days. See observation below for a skier triggered loose wet above NWAC's forecast elevation bands. Active wind loading has not been observed since late last week. Â
Surface conditions are highly variable. On solar aspects, surface melt-freeze crusts reform every night. On shaded and sheltered aspects, settled storm snow is still providing some nice skiing and riding conditions. Many aspects in higher terrain now feature wind stiffened snow. Near surface faceting and surface hoar growth has been reported on colder, non-solar aspects throughout the Cascades. These persistent grain types will become important when snowfall returns and watched as potential future weak layers.Â
Observations
On Wednesday afternoon, Mt. Hood Meadows Pro Patrol reported consolidated snow and no avalanche concerns with some corn developing on south-facing aspects.
NWAC pro-observer Laura Green traveled in the Mitchell/White River drainage on Monday between 5300 and 6600 feet and found many variations in the surface snow but overall a settled and well bonded snowpack with few avalanche concerns in the terrain she covered. She observed surface hoar up to 3-4 mm on non-solar ENE-facing slopes.Â
One skier triggered avalanche was reported on the White River Headwall near Crater Rock on Sunday up to size 2 (see picture). While this slide reaches above NWAC's forecast, it highlights the potential for loose wet avalanches on steep solar aspects. Â
Photo courtesy Mike Schumann 12-10-17
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Avalanche Problems
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.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Unlikely
Expected Size: 1 - 1