Avalanche Forecast

Archived

Jan 15th, 2017–Jan 16th, 2017

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural and human triggered avalanches likely.

Below Treeline

Natural and human triggered avalanches likely.

Regions

Olympics.

Little change in the avalanche danger is expected Monday with recent wind slabs primarily found on N-W-S aspects. However increasing SW winds above treeline may start to form shallow wind slabs on more easterly aspects Monday afternoon. A drastic change in the weather pattern to wetter and milder weather should substantially increase the avalanche danger either Monday night or Tuesday.

Detailed Forecast

Light rain should develop for the Olympics in the afternoon along with increasing SW winds in the afternoon.

Little change in the avalanche danger is expected Monday with recent wind slabs primarily found on N-W-S aspects. However increasing SW winds in the above treeline band may start to form shallow wind slabs on more easterly aspects. Remember that firmer wind transported snow is always your best sign of wind slab layers.

Also, shallow loose wet avalanches are possible on steeper slopes mainly near and below treeline as light rain is expected to develop in the afternoon.

Continue to identify the 12/17 buried PWL in snowpits and avoid areas where the overlying snowpack is shallower such that affecting this layer would be more likely.

Avalanche watch issued Monday night through Tuesday: A drastic change in the weather pattern to wetter and milder weather should substantially increase the avalanche danger either Monday night or Tuesday.

Heavy precipitation with a warming trend Monday night will most likely impact the Olympics including the Hurricane Ridge area. A natural avalanche cycle should occur Monday night.

An abundance of weak and cold snow in the upper snowpack especially near and below treeline combined with the potential for rapid warming and high precipitation rates would lead to very dangerous avalanche conditions during this period and backcountry travel is not recommended. Check the forecast Monday evening for updates.

The 12/17 PWL which has been largely unreactive as of late may awaken during the expected upcoming warm and wet period with the potential to produce large and destructive avalanches down to this layer.

Snowpack Discussion

Weather and Snowpack

A pair of warm fronts moved across the Northwest last weekend causing see-sawing temperatures to near or above freezing for areas away from the Passes including Hurricane Ridge. 6 inches of new snow were reported by NPS staff Monday 1/9 at Hurricane Ridge.

Although the precipitation gage didn't record any tips, NPS web cameras showed steady light snowfall at Hurricane Ridge all day Tuesday with light upslope snow showers. Light N or NE winds were increasing in the afternoon.

An upper ridge over the northeast Pacific Ocean has caused fair weather Thursday through Sunday over the Olympics and Cascades with mostly light winds and moderating temperatures west of the crest and at higher elevations. Hurricane Ridge topped out at 40 degrees on Saturday and Sunday.

Surface hoar and near surface faceting has been noted in the Olympics and Cascades in sun and wind sheltered locations below treeline. Sun crusts have formed on steeper solar aspects over the last few days. The best riding and skiing conditions have generally been reported in less wind and sun affected areas below treeline during this stretch of fair weather.

Recent Observations

NWAC pro-observer, Matt Schonwald was in the field with NPS rangers in the Hurricane Ridge area Friday, 1/6. Matt traveled to Steeple Rock on the Obstruction Peak Road. The persistent weak layer from 12/17 was evident in the two distinct areas where snow tests were performed. The layer ranged in depth from 110 cm on SSW aspect to 135 cm on NW aspect. While reactive in deep snowpack tests and PST's, stiff overlying layers and the fact the layer is deeper than 1 meter make human triggering of this layer unlikely.

NWAC pro-observer Matt Schonwald was out on Klahane Ridge on Friday 1/13 and on a south slope at 5170 feet found about 90 cm of snow with no reactive layers over the 12/17 PWL. The PWL gave a PST60/100 End result so we still need to watch this layer.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.