Avalanche Forecast
Issued: Jan 16th, 2018 11:56AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
NWAC,
Northwest Avalanche Center
Light to moderate snow Wednesday morning will add to the development of shallow wind slabs above treeline. Mitigate hazard by approaching lee slopes with caution and observing wind transported snow, which may extend into the near treeline zone in areas that see more snowfall than anticipated.
Summary
Detailed Forecast
This discussion only applies to the Cascade West-Central and Cascade West-South zones.
Most areas in the central and south Cascades will see 2-4 hours of light to moderate rain and snow in the morning hours, with increasing moderate SE winds, and sharp warming during the late morning hours. Moderate to locally heavy rain will arrive in the evening.
Recent wet snow should be bonding well to firm surfaces in most areas. Recent gusty SW winds may have created shallow slabs in the above treeline areas. Additional snowfall Wednesday morning above 4500 feet will create shallow wind slabs as generally SE winds load lee slopes above and perhaps near treeline. Generally watch for active snow transport and navigate away from wind-loaded slopes, where small avalanches may be triggered on W-N-E aspects.
There will not be enough new snow to develop storm slab or wind slab below treeline.
Loose wet avalanches will not be listed as a problem, but they are not out of the question with heavier rain arriving very late in the day.
Snowpack Discussion
Across the west slopes of the Cascades, many locations near and above treeline received 2-4" of higher density snow Wednesday. Locally higher amounts were seen near Mt. Baker, especially above treeline. Moderate winds, with strong gusts, are locally transporting this shallow new snow around on Wednesday afternoon, most notably at Mt. Baker.
Recent snowfall sits on a firm crust at higher elevations and refreezing or still wet snow at lower elevations.
After 3 extraordinarily warm days of high pressure (Saturday-Monday), the snow from late last week is well consolidated and sits on a thin crust (Jan. 9) which may be found in the near treeline elevation band in most areas. A more supportable and thicker crust (Jan. 5) from rain or freezing rain is easily identifiable in the upper snowpack.
Below the 1/5 crust, observations continue to indicate a strong snowpack with no notable layers of concern.
Observations
North
Large natural and skier-triggered loose wet avalanches were reported on Sunday in the Twin Lakes area by Baker Pro Patrol and Hidden Lake Peak area via our public observations page.
Central
No recent observations
South
No recent observations
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: All aspects.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Jan 17th, 2018 11:56AM
