Avalanche Forecast
Issued: Dec 5th, 2017 10:00AM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Loose Wet.
NWAC,
Northwest Avalanche Center
Watch for small areas of firmer, wind-transported snow on isolated, lee terrain features. Watch for loose-wet snow avalanches releasing from sun exposed rock faces or below cliffs or rock bands.
Tree well hazard may still exist: Travel with a partner and keep them in sight and in communication in areas where there has been recent heavy snowfall.
Summary
Detailed Forecast
Continued sunny and mild weather is expected Wednesday with some moderate to strong crest level easterly winds.
This should allow for further settlement of the recent storm layers and cause an overall slowly decreasing danger.
Small wind slabs may exist on a variety of aspects, mainly on exposed lee slopes receiving any transported snow. The warming surface snow should limit or end further transport. Any remaining wind slabs are expected to be stubborn or difficult to trigger. Watch for small areas of firmer, wind-transported snow on isolated, lee terrain features.
Continue to watch for isolated, small, loose wet avalanches on steep sun exposed terrain during the late morning or afternoon, especially on unsupported slopes or near rocks.
Early season terrain hazards still exist, such as poorly covered rocks, vegetation and creeks, particularly at lower elevations.
Travel with a partner and keep them in sight and in communication in areas where there has been recent heavy snowfall due to tree well danger.
Snowpack Discussion
Warm, very wet weather before Thanksgiving caused wet snow and glide avalanches as well as snowpack consolidation, leaving a strong crust as a gift. There are no snowpack concerns below the Thanksgiving crust and in general new snow received post-Thanksgiving has reportedly bonded well.
A series of frontal systems produced snow over the week following Thanksgiving at all stations in the Cascades: Locations on the west side of the Cascade crest received 1.5' to 4.5' with the most at Mt. Baker.
This includes the most recent 2 day total snowfall ending Sunday morning along the Cascade west slopes, ranging from 5-27" with the most again at Mt. Baker.
The recent storm cycle ending early Sunday with 3-6 inches of snowpack settlement by Tuesday afternoon.
Observations
North
Storm slabs were sensitive early Saturday, however, by Sunday, the Mt. Baker ski patrol reported many folks were skiing in the backcountry with no avalanches reported. Additionally, a private report to NWAC indicated small, thin wind slab high on north-facing slopes near the Mt. Baker ski area. Otherwise, no signs of instability. Plenty of point releases on S-facing slopes during sun breaks.
On Sunday, a Professional Guide was skiing in the Bagley Lakes area and despite many back-country skiers, saw only one small triggered shallow wind slab in a steep, loaded location. Layers from Friday were less reactive and healing.
Central
On Sunday, NWAC observer Jeremy Allyn was in the Alpental/Source Lake area. A lot of recent storm snow hasn't fully settled and there were still some storm layers giving moderate RP results in snow pit tests. Pockets of wind affected snow seen on high terrain. The low-density snow was deep and tree wells were a major hazard.
By Tuesday, observations in the Alpental valley indicated sun and warming were quickly creating moist surface snow with several small loose-wet slides releasing from rock or unsupported features exposed to direct sun.
South
NWAC Pro Observer, Dallas Glass was out on Saturday in the Paradise area. On W-S-E aspects he found 8” new of new snow, well-bonded to 2 feet of previous snow on the Thanksgiving crust. He found 5400-6000’ W-SW-S-SE-E. He did not find evidence of storm or wind slab.
On Sunday, Crystal Mountain Ski Patrol reported 10” of new snow in the last 24 hours. The upper snowpack is generally right-side up and well-bonded to the Thanksgiving day crust. Winds on Saturday night also created a shallow surface layer of higher density snow giving minor cracking and likely small, shallow areas of wind slab.
Another Pro Observer was at Paradise on Sunday where the main story was the 9-10" of new snow that fell at slightly higher densities and precipitation rates, giving small storm slab on varied aspects. Several small loose-dry avalanches were observed in the near tree-line.
NWAC observer, Ian Nicholson, travelled in the Crystal back country Tuesday, finding new shallow wind slabs that had formed overnight from increasing easterly crest level winds. These were small and isolated to features near ridges, causing terrain choices to be altered to avoid exposure to obvious wind loaded pockets. By afternoon, surface snow had become moist on any solar facing slopes, from E-SW, ending further wind transport.
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, Treeline.
Likelihood
Expected Size
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.
Elevations: Treeline, Below Treeline.
Likelihood
Expected Size
Valid until: Dec 6th, 2017 10:00AM
