The bottom line: Winds have been moving lots of snow, so you can very easily trigger a destructive wind slab near and near treeline. Avoid all wind-loaded slopes at upper elevations and keep checking for shallow storm slabs in lower-elevation sheltered terrain.
Snow and Avalanche Discussion
Updated 7:30 AM due to lower than anticipated snowfall. Avalanche danger may peak later in the day as a powerful warm front brings increasingly stormy conditions in the afternoon. Be prepared to dial back your plans if the weather deteriorates.
Regional Synopsis
January 16, 2019
Since Friday January 11, we’ve enjoyed a spell of generally nice weather in the mountains. This allowed for some great views, enjoyable outings, and lots of snow observations. A more active weather pattern beginning Thursday January 17th will bring this nice weather to a close.
During this time period, the snow surfaces around the area have changed dramatically. This forms the foundation for a few current trends we are seeing in the mountains.
New Snow Problems
Reports from around the area indicate a wide variety of snow surface conditions prior to new snow on January 17th. We’ve heard about breakable crust, very icy surfaces, sugar facets, surface hoar, and rime. What snow surface you encounter can depend on aspect, elevations, and general location.
As a series of winter storms impact the area, how will the new snow bond to the old snow surface. This can be tricky to predict. As the snow starts to pile up make lots of shallow snow observations. Shovel tilt test, hand shears, and small slope test can all help you track how the new snow is bonding to the old snow at different aspects and elevations. Stop and take a look at where the snow is failing. Do you see large grains of snow? Do they look like feathers? Do the act like sugar? How far below the current snow surface are they?
Old Snow Problems
There are still lingering persistent weak layers in the eastern zones of the cascades. You are most likely to find weak older snow in areas further east from the Cascade crest where snowpacks are shallower, more variable, and generally weaker. In some locations weak snow near the ground can still be found. These basal facets have hung around all season. The only way to gain information about these old persistent weak layers is to get out your shovel and dig. Because of the size of our forecast zones and the variability in the snowpack, it's important to make snow observations as you travel. We’ll keep watching these old layers, but let us know what you see while you are in the mountains.
Avalanche Problems
Wind Slabs
While snowfall totals Thursday night have been less-than-impressive, the winds have been transporting a lot of recent snow. Expect large to very large and sensitive wind slabs at upper elevations and you will be able to trigger them.
Mt. Hood Meadows Pro Patrol found that the 5-6” of snow that fell at high intensities Wednesday evening was blown into 12-18” reactive soft slabs that were running full path above 6,600 ft. These wind slabs were running on a thin layer of snow that sits above the most recent crust. The same interface or a new storm layer may be the culprit tomorrow.
Today is not a day to play in or near large, potentially wind-loaded slopes. If you travel on a potentially wind-loaded aspect, stick to densely wooded or low-angle slopes well away from slopes where avalanches start, stop, or run.
Aspects:
All aspects.
Elevations:
Alpine, Treeline.
Likelihood: Likely
Expected Size: 2 - 3
Storm Slabs
Updated 7:15 Friday morning due to less than expected snowfall. Warming on Thursday created a reactive slab below treeline from the snow that fell at Mt. Hood Meadows Wednesday night. 2" of new snow fell overnight. With minimal new snow input early int the day, we are not sure whether old or new snow interfaces will be reactive, but additional snowfall late in the day may cause the storm slab problem to increase. Dig down to the most recent crust and check all old and new snow interfaces. Use skin track tests and small test slopes to identify reactive snow and if heavy snow falls, use lower-angle supported slopes for safe travel.
