Avalanche Forecast
Regions: Olympics.
A mixed bag of conditions is possible in the Olympics and Cascades on Sunday. New mostly shallow wind slab Sunday afternoon has been emphasized in the Olympics.
Detailed Forecast
A weakening front will move over the upper ridge and cause increasing alpine winds on Sunday. It should still be mild or rather warm through the morning hours. Then light to moderate rain or snow should spread to the Olympics with a cooling trend by Sunday afternoon.
In the Olympics the main avalanche problem should be new mostly shallow wind slab Sunday afternoon. This should be mainly on northwest to southeast slopes near and above treeline but watch for new or older firm wind transported snow on all aspects in the upper terrain bands.
Snowpack Discussion
Weather and Snowpack
An arctic air mass settled over the Northwest with fair, very cold weather the second week of January.
An atmospheric river arrived over the Northwest Tuesday 1/17 with heavy rain seen up to at least 6000 feet in the Hurricane Ridge area. Three day precipitation totals through Thursday 1/19 were about 2.5 inches at Hurricane Ridge. An avalanche cycle likely occurred in the Olympics during this period.
The NPS rangers reported a storm total of 15 inches of snow at the Hurricane Ridge manual snow plot Thursday morning 1/19. Showers continued during the day but our precipitation gage didn't record any precipitation after 9 am due to equipment problems. About a foot of snow fell at the Waterhole NRCS Snotel over a 24 hour period ending Friday morning 1/20.Â
Showers late Saturday 1/21 and another band Sunday 1/22 deposited about 4-6 inches of new snow as of Sunday afternoon at Hurricane, with strong S-SE winds.
Fair weather with light winds and cool temperatures have been seen Monday through Wednesday.
A large upper ridge and warm air mass built over the Northwest Thursday to Saturday. By Saturday temperatures reached the 40's at Hurricane.
Recent Observations
NWAC pro-observer, Matt Schonwald, was at Hurricane Ridge Friday 1/20. Matt found 10 inches of settled recent storm snow generally well bonded to the underlying rain crust and not reactive. SE winds were forming shallow wind slabs on lee slopes near treeline. The recent rainfall had penetrated well into the snowpack. At a limited number of test sites, the 12/17 PWL was found to be rounding and unreactive in snowpit test and well over a meter down. We feel comfortable removing the persistent slab from the avalanche problem list moving forward.
A report from Klahane Ridge via the NWAC Observations page on Sunday indicated wind loading on the N slopes at 6000 feet. The rain had penetrated to about 3 feet in the snowpack and the 12/17 layer we have been tracking was well bonded and difficult to identify.
Avalanche 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: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood: Possible
Expected Size: 1 - 1