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Avalanche Forecast

Archived

Jan 25th, 2017–Jan 26th, 2017

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Thursday's avalanche danger will consist of a mix of lingering wind slab near and above treeline and loose wet avalanches on solar slopes if extended sunbreaks materialize during the afternoon.   

Detailed Forecast

Generally cloudy weather with light winds should be seen on Thursday although there may be some sunbreaks in the afternoon. A slow warming trend begins Thursday.  

These conditions will continue to help recent wind and storm slabs settle and further stabilize. Lingering wind slabs are most likely on SW-NW-NE aspects due to recent strong E-SE transport winds over the weekend. Watch for recent wind effects near and below ridgelines and avoid steep slopes with obvious signs of recent wind loading. 

Watch for loose wet snow conditions on steep solar slopes if the sun pops out for an extended period of time on Thursday afternoon. 

Snowpack Discussion

Weather and Snowpack

An arctic air mass settled over the Northwest with fair, cold weather from the New Year through the second week of January. An atmospheric river moved over the Northwest about 1/17-1/18 with heavy rain seen up to about 5500 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 Thursday 1/19, but our precipitation gage didn't record any precipitation after 9 am, possibly 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. 

Showers late Saturday and another band Sunday 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.

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 N slopes at 6000 feet. Rain had penetrated to 1 m in the snowpack and the 12/17 layer was well bonded and difficult to identify.

Problems

Wind Slabs

Wind Slab avalanches are the 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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.