Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Jan 18th, 2017–Jan 19th, 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.

The snowpack in the Olympics and Cascades is undergoing a lot of change and there is less than the usual certainty in which avalanche problems and danger levels to indicate. It might be a good plan to wait until Friday when conditions are better known and should be more stable.

Detailed Forecast

Winds and snow showers will decrease Wednesday night and Thursday with cooler temperatures.

The greatest likelihood of new wind slab should be above the Hurricane elevations where storm snowfall is heavier. Underlying crusts may make wind slab sensitive on some slopes.

New storm slab will be most likely in any areas that experience rapidly accumulating snow of more than an inch an hour for several hours. Underlying crusts may make storm slab sensitive as well on some slopes.

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.

Wet slab or glide avalanches may also be possible for another day in the below treeline on Thursday while water from the atmospheric river drains from the snowpack. While this won't be listed as an avalanche problem in the Olympics on Thursday but avoid areas below unsupported steep terrain without trees in the below treeline especially if the slope is known to have a smooth ground surface.

The snowpack in the Olympics and Cascades is undergoing a lot of change and there is less than the usual certainty in which avalanche problems and danger levels to indicate. It might be a good plan to wait until Friday when conditions are better known and should be more stable.

Snowpack Discussion

Weather and Snowpack

An Arctic air mass was over the Northwest with fair, cold weather last week. Surface hoar and near surface faceted crystals probably formed in most areas during that period.

A drastic change was seen when an atmospheric river moved to the Northwest Tuesday and Wednesday. This caused heavy rain up to about 5500 feet at Hurricane. An avalanche cycle is expected to have occurred in some or many areas including Hurricane.

Observations the next couple days should help determine to what extent any of the surface hoar and near surface faceted crystals from the fair cold weather might have survived the atmospheric river event.

Recent Observations

The last observation for the Hurricane area is from NWAC pro-observer Matt Schonwald on Klahane Ridge on Friday, 1/13. He found 90 cm of snow with no reactive layers over the 12/17 PWL on a south slope at 5170 feet. But 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.

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.