Avalanche Forecast
Jan 16th, 2019–Jan 17th, 2019
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3:
Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3:
Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3:
Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3:
Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3:
Considerable
The avalanche danger rating below treeline will be considerable
Regions: Mt Hood.
The bottom line: Avalanche conditions will deteriorate dramatically throughout the day as increasing snow and wind form large and reactive slabs. These slabs likely sit on a thin layer of potentially weaker surface snow existing prior to the storm. As the storm intensifies, dial back your terrain selection.
Avalanche Discussion
A professional observer in the Mt. Hood area found breakable crusts on solar aspects (1-2.5†thick) and non-solar aspects (<1†thick) below treeline in the Newton/Clark drainages. A thin layer of new snow sits on that crust. The fresh snow was bonding moderately well with the crust.
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.
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.
Weather Forecast
Weather Synopsis for Wednesday night through Friday
A strong closed low slowly weakening and filling off the California coast is beginning to veer northward while it sends a chunk of energy directly into California. Wednesday night, a weakening band of moisture will lift northward and spread moderate snowfall to Mt. Hood and the east slopes of the southern WA Cascades with lighter snowfall for other areas.
On Thursday, expect increasing S then SW flow as the low tracks about 250 miles off our coastline, with continued cool easterly flow through the passes. Periods of light snow are expected with higher snow levels west of the Cascade crest. The main energy with the low will arrive from the SW late Thursday, bringing moderate rain and snow throughout the region into Thursday night. A wind shift late Thursday night is likely to change Snoqualmie pass to rain, but slightly higher elevations will remain snow.
On Friday, rain and snow showers will decrease as the initial low departs, but a second low tracking to our NW, well offshore, will spread increasing moisture to our coastal regions late in the day as snow levels rise.
Avalanche Problems
Wind Slabs
1.25” of snow water will be blown around under increasingly strong winds on Thursday. WInd slabs will become increasingly reactive throughout the day near and above treeline. Thes slabs may form a density interface with the recent snow that fell early on 01/16 or it may fall on weak, faceted, or rimed surfaces at higher elevations. With potential weak layers and bed surfaces in play, increasing snow and wind will drive the avalanche danger higher Thursday afternoon as slabs build in extent and thickness. You are most likely to trigger a wind slab where winds have been actively loading a slope. Active snow transport, fresh cornices, and rounded snow slopes may indicate that wind slabs inhabit the terrain. Before you set out, create a travel plan that allows you a safe exit on lower-angle terrain if conditions deteriorate. Avoid potentially wind-loaded slopes greater than 35 degrees.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 2 - 2
Storm Slabs
Higher snowfall rates will create storm slabs in sheltered locations, likely sitting on weaker snow above a crust. This is a good recipe for avalanches. Retreat to supported slopes less than 35 degrees if you find more than 6” of new snow forming a cohesive slab.
Aspects: All aspects.
Elevations: Below Treeline.
Likelihood: Possible
Expected Size: 1 - 1