Avalanche Forecast

Archived

Mar 8th, 2016–Mar 9th, 2016

Alpine

Natural and human triggered avalanches likely.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches possible, human triggered probable.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches possible, human triggered probable.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Olympics.

Significantly changing weather and snow conditions should be seen in the Olympics Wednesday afternoon. Travel in avalanche terrain above treeline is not recommended Wednesday afternoon. Dangerous conditions should also be seen in the near and below treeline.

Detailed Forecast

A weakening front should move over the Northwest Tuesday afternoon and night. This may cause some mostly light amounts of snow but probably not as much as earlier expected.

The bigger story is the incoming atmospheric river on Wednesday. A warm front should south to north over the Olympics and Cascades Wednesday morning to afternoon. This should bring stormy wet weather with rising snow levels initially to Mt Hood Wednesday morning and to the Olympics and Washington Cascades Wednesday afternoon.

Little change may be seen by Wednesday morning in the Olympics. But by Wednesday afternoon watch for increasing alpine winds and increasing moderate to heavy rain or snow and rising snow levels.

Mainly in the above treeline new wind slab of increasing density due to warming is very likely to form on lee slopes. Watch for firmer wind transported snow as the storm develops Wednesday afternoon.

Also mainly in the above treeline new storm slab of increasing density is also very likely due to warming. Watch for snowfall that begins to accumulate Wednesday afternoon at more than an inch an hour.

Rain in the below and possibly in the near tree line starting Wednesday afternoon is also likely to create loose wet avalanche conditions. Watch for pinwheels and natural loose wet avalanches.

The rain where heavy enough by Wednesday afternoon may activate previous layers and cause releases of previous wind slab layers or wet slab avalanches mainly in the near and below treeline.

Snowpack Discussion

Weather and Snowpack

Last week was wet and relatively mild with a series of active fronts transiting the region resulting in fluctuating freezing levels and periods of very strong winds.

A front Sunday brought about a foot of snow to Hurricane by Monday morning. No new snow was reported Tuesday morning.

The mid and lower snow pack in the Olympics should generally be a stable mix of crusts and layers of moist and rounded snow crystals.

Recent Observations

The ranger at Hurricane reported a foot of new snow on Monday morning with snow sliding off the road cuts and onto the road in many places. The Sunrise path on a northeast slope about a 1/2 mile from the visitor center released an avalanche that entrained snow to about 1' and became 100 feet wide although it could not be determined if it was a loose or slab avalanches due to low visibility.

On Tuesday the ranger added that there had been many 6-12 inch storm slab avalanches on Monday.

Hurricane Weather Station

Internet communications to the station have been disrupted but will hopefully be restored soon.

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.

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.