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Archived

Avalanche Forecast

Feb 19th, 2017–Feb 20th, 2017
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low
Alpine
2: Moderate
The avalanche danger rating in the alpine will be moderate
Treeline
1: Low
The avalanche danger rating at treeline will be low
Below Treeline
1: Low
The avalanche danger rating below treeline will be low

Regions: Olympics.

Generally safe avalanche conditions are expected at Hurricane on Monday. Watch for new shallow wind slab on lee slopes. Take care to avoid an uncontrolled fall on steep slopes with a smooth surface crust. 

Detailed Forecast

Weakening low pressure systems will pass near Cape Flattery on Sunday and near Astoria on Monday. This will generally cause a trend of increasing alpine winds and increasing snow especially in the south Cascades by Monday. Temperatures should not change greatly through Monday. But much of this snow will miss Hurricane Ridge. Expect a few inches of new snow at Hurricane on Sunday and Monday.

The size and extent of wind slab may slightly increase on Monday at Hurricane. Watch for firmer wind transported snow on potential lee slopes. Significant winds lately and on Monday will have been mostly south to southwest so north to southeast aspects will be indicated but keep an eye on all aspects.

There isn't expected to be enough sustained snowfall on Sunday and Monday at Hurricane for new storm slab so this won't be indicated as an avalanche problem. But reevaluate if you experience more than a few inches of rapidly accumulating snowfall.

Loose wet avalanches will not be indicated as an avalanche problem but watch for loose wet surface snow if you find yourself on solar slopes during cloud or sun breaks.

Snowpack Discussion

Weather and Snowpack

Hopefully the last atmospheric river of the season arrived on Valentines Day 2/14 bringing another round of heavy rain, avalanches, crusts and consolidation through Thursday in the Olympics. Minor snow was seen at Hurricane at the tail end of the storm.

A short period of fair weather on Friday 2/17 caused another surface crust.

Some snow was seen with light winds on Saturday. The NWAC station and the rangers at Hurricane indicate only 1-2 inches ending Sunday morning.

Temperatures haven't changed much on Friday to Sunday.

Recent Observations

NWAC pro observer Matt Schonwald traveled to the Hurricane Hill region Friday. A hard, slick surface crust made travel precarious early Friday before the sun and warming began softening the crust. The few inches of snow fell during the tail end of the storm had bonded well and filled in many rain runnels, helping to smooth surface conditions. There was little evidence that the latest rain event produced any avalanches. The main hazard in the Hurricane area appeared to be an uncontrolled fall on the slick crust.

An observation via the NWAC Observations page for Hurricane reports a sizeable loose wet avalanche on the W-SW side of Steeple Rock that probably occurred during the 2/14-2/16 period.

Avalanche 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: North, North East, East, South East, North West.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 1 - 1