Avalanche Advisory Jan 14

Avalanche Advisory January 14, 2018

Bottom Line

The Avalanche Hazard is Moderate today. It is possible that we could see some natural avalanches on slopes that receive direct solar radiation as the snow warms up today. Moderate hazard also means that human triggered avalanches are possible on certain slopes today. Variable depths and stability exist throughout the advisory area Play it conservative, watch for signs of warming like rollerballs and point releases.

Avalanche Problem #1: Wet Slab

Wet slides are likely today as the snow struggles with warming temperatures. Watch for signs like pinwheels or rollerballs, and move to cooler slopes that are not receiving as much direct sunlight, We are going to see temperatures climb to nearly 40 degrees in the upper elevations today, and Sunlight for the first time on the new snow.

Avalanche Problem #2: Persistent Slab

Throughout the advisory area we have found a highly variable snowpack with depths ranging from a few feet to just over 6 feet. The only thing we found in common throughout the snowpack were shallow instabilities in the new snow that lacked significant propagation potential. Pit tests and some large cornice bombs showed us the potential for sluffing or loose, dry avalanches on steep terrain and the potential for small soft, storm slabs that were failing around 25-30 cm down from the surface. HOWEVER: the deeper, weak layer of faceted snow was still present above the Thanksgiving Crust at 7700 feet on an East aspect although it was not affected by our pit tests. Closer to 8200 feet we found the faceted layer on a shallow rocky north aspect to be fairly well defined but lacked the crust below it. It failed when we isolated our test column. 3 feet further over in the same pit we had no results where the snow was nearly 6 feet deep and the faceted layer proved to be unreactive even under hard force. Thursday we found the Thanksgiving rain crust/facet combination to be extremely reactive in the Lick Creek Drainage on an East facing slope near 7700 feet.

The bottom line is that the snowpack is still wildly variable on different aspects and in different elevations and areas. The weak layer of faceted snow above the Thanksgiving Rain Crust is still persisting in the snow pack on nearly every aspect. The strength of this layer is wildly variable with stability results ranging from confidence inspiring to very concerning have been documented this week. The potential for a shallow avalanche stepping down into this layer also exists in areas where the weak layer is more buried less deeply. Variability is the name of the game right now and that means there is no yes or no answer about which slopes are safer to travel on. Cautious, informed decision making is mandatory for safe travel right now. The potential of triggering an avalanche in this layer is like rolling the dice right now and the consequences are significant. See this short video for a better look at what we found in our pit tests on Thursday. This layer also has been creating problems in areas adjacent to the PAC advisory area; Mores Creek Summit near Boise experienced a significant natural avalanche cycle on the persistent weak layer Thursday night.

Weather

.SHORT TERM…Today through Monday night…Fog is impacting areas
around McCall, ID and Baker City, OR this morning. Additional low
lying locations remain in the fog threat this morning, especially
the Lower Treasure Valley and portions of eastern Oregon (Burns
and Baker City). High resolution models agree that much of the
Upper Treasure Valley and Western Magic Valley look to generally
stay out of fog this morning with mostly clear to partly cloudy
skies expected. Dry conditions expected today under the ridge,
with the threat of fog returning again tonight. Fog locations may
increase to include portions of the Upper Treasure Valley as
models indicate a more favorable environment for development. Most
fog development should lift by the late morning hours. The next
forecast challenge is the arrival of the cold front/trough on
Monday night. Models continue to slow down the progress of this
system, so the forecast has been trimmed back on precipitation
coverage and wind impacts for Monday night. Temperatures expected
to remain above normal through the period.

.LONG TERM…Tuesday through Saturday…A return to unsettled weather
expected in the long term, with appreciable mountain snowfall. A
shortwave will track across the region into Wednesday morning,
bringing widespread precipitation. The system is expected to weaken
considerably as it moves across SE Oregon into Idaho. At this time,
precipitation amounts will be heaviest in northern Malheur and Baker
Counties, and lesser across the rest of the forecast area. Travel
across Baker County may be difficult with this system, as snow
levels range from 3000-3500ft during the bulk of the precipitation.
Drier conditions are expected on Wednesday afternoon as a weak ridge
passes over the area. Southwest flow develops, bringing warmer
temperatures, in response to a deep upper level trough off the Pac
NW coast. A cold front will approach the region on Thursday,
bringing valley rain and mountain snow above 4500ft in Baker County
to 6500-7500ft south of the Snake Plain toward the NV border. With
the cold frontal passage, snow levels lower to the valley floors by
Friday night. A shortwave embedded in the main upper level trough
moves across the region late Friday night into Saturday morning,
with scattered snow showers across the area, including the valleys.
Showers will taper off on Saturday afternoon before the next system
begins to impact the region on Sunday. Stay tuned.

Recent Observations

Yesterday, we toured out to Lava Butte We were seeing point releases and rollerballs. The conditions made it very hard to see, and the snow was deep and warm. Visibility was a challenge as ice formed on goggle lenses repeatedly. The snowpack further north was thinner and lacked the coverage elsewhere. Our test pit was not inspiring, and showed a wet, not frozen shallow snowpack. We were getting moderate results in compression on the new snow, but no propagation in an ECT.

A very warm misty cloud saturating the snow surface

Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.

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