Avalanche Forecast
Regions: Olympics.
The avalanche danger should decrease on Saturday but the decrease will be a moving target and careful snowpack evaluation and cautious routefinding will be essential.
Detailed Forecast
Decreasing winds and mostly light snow showers should be seen over the Olympics on Saturday with much lower snow levels and much cooler temperatures. Not a lot of snow is expected following the front Friday but we will see how it goes. The avalanche danger should decrease on Saturday but the decrease will be a moving target and careful snowpack evaluation and cautious routefinding will be essential.
Layers of recent or new wind and storm slab may need a day to mostly stabilize. Water may also need a day to drain from the upper snow pack below about 3-4000 feet.
Recent moderate to strong southwest to west winds will make wind slab most likely on northwest to southeast slopes but keep an eye out on all aspects in areas of more complex terrain. Watch for firmer wind transported snow from Friday and possible deeper wind transported layers such as from Tuesday.
New storm slab formed on Friday may need a day to mostly stabilize on Saturday. Storm slab is most likely in area that experienced more than a few hours of rapidly accumulating snow.
Cornices won't be listed as an avalanche problem in this area but avoid areas on ridges and mountain tops were a cornice might be present and avoid slopes below cornices.
Snowpack Discussion
Weather and Snowpack
The most recent wet warm storm arrived on Valentines Day 2/14 and formed the uppermost, very strong rain crust in the snowpack.Â
A series of disturbances in cool, NW flow aloft from Saturday 2/25 through Tuesday 2/28 deposited about 10 inches of snow at Hurricane. Very strong alpine winds were seen in most of the Olympics and Cascades on Tuesday.
Southwest flow aloft began to ramp up again on Thursday as the first in a new series of fronts crossed the Northwest. Strong southwest flow is carrying a second stronger front across the Northwest on Friday evening. At Hurricane this will be causing strong SSW alpine winds and moist, dense new snow above about 3-4000 ft and wet snow or rain below about 3-4000 ft.
Recent Observations
NWAC observer Matt Schonwald was Hurricane on Friday and found that ski tests were showing rapidly increasing propagation and increasing sensitivity of deepening storm slab. Previous winds had loaded various slope aspects while south winds on Friday were loading N aspects.Â
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: Likely
Expected Size: 1 - 1
Storm Slabs
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. 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.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Storm slabs usually stabilize within a few days, and release at or below the trigger point. They exist throughout the terrain, and can be avoided by waiting for the storm snow to stabilize.
Aspects: All aspects.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 1