Avalanche Forecast
Regions: Olympics.
Increasing high danger is expected at Hurricane Ridge at least near and above treeline Sunday afternoon and evening
Detailed Forecast
The next very strong cold front will begin to reach the Olympics Sunday midday. This will begin to cause stormy weather with strong winds and heavy snowfall. This system should have cooler temperatures and lower snow levels than the past few systems. Rapid loading should begin to cause new storm slab to begin to build on most sheltered aspects in all the elevations zones Sunday afternoon. Wind transport should cause new wind slab to begin to build on lee slopes mainly near and above treeline. This will begin to add further loads to the rain crust from Wednesday or deep layers. Natural or triggered large avalanches should become possible Sunday midday.
The storm should peak in the Olympics Sunday afternoon and evening. Rapid loading and wind transport will cause storm and wind slab to further build and become deep Sunday afternoon and evening. An avalanche cycle is likely in the near and above treeline zones. Natural or triggered large avalanches are likely near and above treeline Sunday afternoon and evening.
Snowpack Discussion
Recent Regional Weather and Snowpack
An extended dry mild period was seen the latter half of January. The was followed by very cold weather and periods of low density snowfall in early February. Now for the past 5 days the Northwest is getting pummeled by daily frontal systems producing periods of strong winds, periods of warmer higher density snowfall and rain during periods of generally warmer temperatures.
Water equivalents/snow for the past 5 days mostly range as follows: Olympics and Cascades near and west of the crest 3-7 inches WE/2-4 feet of snow, east of the crest 1-4 inches WE/1-2 feet of snow, and at Mt Hood 10-12 inches WE/2-3 feet of snow! Note this is generally heavy wet snow for all areas especially at Mt Hood!
Regionally this weather is generally building heavy denser snow layers over colder lower density and faceted snow from early February over potential hoar frost, faceted snow and crusts from late January. So it is no surprise there has generally been a lot of regional avalanche activity especially in the Washington Cascades and at Mt Hood the past couple days. Several widespread natural avalanche cycles have run their course over the past several days with the largest cycle occurring late Tuesday to early Wednesday.
Similar weather and snowpack structures around the west have lead to numerous recent fatal avalanche accidents including in northeast Oregon on Tuesday.
Hurricane Ridge
Our NWAC observer Tyler Reid at Hurricane Ridge on Friday reported a ski triggered D2 avalanche on a northeast slope at 5200 feet. He is also reported 20 cm of F storm snow over a rain crust from Wednesday over another 20 cm of F snow. The crust layer at 20 cm will probably be the interface to watch during the upcoming storm on Sunday.
Photo by NWAC observer Tyler Reid showing F over crust over F snow on 14 February.
Snow pit tests by Tyler on Saturday gave moderate to hard, sudden planar results and unlikely propagation.
Limited snow at the lowest elevations will limit the avalanche danger there. The mid and base pack should still consist of mostly stable crusts and melt form layers from periods of warm weather earlier this winter.
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Avalanche Problems
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
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.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 1