Avalanche Forecast
Regions: Olympics.
The avalanche danger Friday should focus primarily on wet snow avalanches, especially on solar slopes during extended sunbreaks or filtered sunshine during the afternoon. Older wind slabs should be unlikely, but may linger near and above treeline on specific terrain features.
Detailed Forecast
Mainly high clouds are expected Friday with light winds and a continued warming trend. Freezing levels should climb to near 6000 feet in the Olympics Friday. Â
Watch for loose wet snow conditions on steep solar slopes during sun breaks or thin high clouds, especially during the warmest part of the day, Friday afternoon.Â
With a lack of midweek observations, we are still listing wind slabs as an avalanche problem, however, in the Cascades the older wind slabs have bonded and are no longer reactive. Any lingering older wind slabs will continue to strengthen and stabilize Friday. Lingering wind slabs are more likely on SW-NW-NE aspects due to strong E-SE transport winds last weekend. Watch for recent wind effects near and below ridgelines and avoid steep slopes with obvious signs of recent wind loading.Â
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.Â
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.
Light winds with warm air aloft allowed temperatures to climb above freezing midday Thursday at Hurricane Ridge.
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
Loose Wet
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. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. 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.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Several loose wet avalanches, and lots of pinwheels and roller balls.
Loose wet avalanches occur where water is running through the snowpack, and release at or below the trigger point. Avoid terrain traps such as cliffs, gullies, or tree wells. Exit avalanche terrain when you see pinwheels, roller balls, a slushy surface, or during rain-on-snow events.
Aspects: South East, South, South West.
Elevations: All elevations.
Likelihood: Possible
Expected Size: 1 - 1
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, South West, West, North West.
Elevations: Alpine.
Likelihood: Unlikely
Expected Size: 1 - 1