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West Slopes North - Canadian Border to Skagit River

Issued: 8:31 PM PST Thursday, January 18, 2018
by Kenny Kramer

NWAC avalanche forecasts apply to backcountry avalanche terrain in the Olympics, Washington Cascades and Mt Hood area. These forecasts do not apply to developed ski areas, avalanche terrain affecting highways and higher terrain on the volcanic peaks above the Cascade crest level. 

While mid and lower elevations have had a great deal of rain, there is DEEP new snow above the rain line. Heavy snow and very strong winds above treeline mean there are dangerous avalanche conditions right now and travel above treeline is not recommended and should be avoided Friday.  Conditions below this weeks rain line are less dangerous, but cautious route finding remains essential because you will be able able to trigger avalanches in the new snow that is becoming deeper.  Dangerous wind and storm slabs are thickening near and below treeline.

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Avalanche Problems for Friday

Wind Slabi

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.

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Storm Slabsi

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.

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Avalanche Summary:

In the Mt Baker area, over 4 inches of water equivalent has fallen since Tuesday night! Winds have ranged in the 40-60 mph range much of that time. Above treeline, much if not all that water has fallen as snow, likely 3-4 feet! The combination of heavy snowfall and very strong winds are making very dangerous avalanche conditions above treeline where deep wind and storm slabs have formed.

Near and below treeline the precipitation began as rain and transitioned to snow. This has caused less dangerous conditions with new snow forming good bonding to the old rain soaked snowpack. However, heavy snowfall and moderate to strong winds have built increasing wind and storm slabs at progressively lower elevations. There are still dangerous avalanche conditions with new and increasingly deep wind and storm slabs deeper of 1-2 feet as of late Thursday.

The old rain wet snow continues to gradually re-freeze and form a new crust layer.

The older snowpack has undergone several rain or warm periods and remains void of any significant layers of concern.

Observations

North

Thursday morning, the Mt Baker Pro Patrol reported fresh wind slabs were sensitive to ski cuts and were releasing in the 4-5 inch range, near treeline. Winds were reportedly very strong along ridges and actively transporting the new snow. 

On Wednesday afternoon, Mt. Baker Pro Patrol observed evidence of several large, natural loose wet avalanches visible on Shuksan arm at approximately 3000 ft. The avalanches are suspected to be from earlier Wednesday. 

Central

NWAC forecaster, Dallas Glass was on Skyline Ridge at Stevens Pass Thursday and reported new storm snow of 8 inches at 4000 feet and 14 inches above 5000 feet. The bonding was good to the old rain wet snow. The crust had yet to re-freeze but was in the process. There was evidence of recent wind transport with a fresh natural avalanche having released on a steep east face about 5300 feet, likely during a brief warm up Wednesday night. There were storm slab layers noted from fluctuating temperatures overnight, but were not sensitive to human trigger in that location. 

South

No recent observations

Forecast for Friday:

Cool temperatures, moderate snow showers and periods of moderate S-SW winds will continue to deposit new snow and further build existing wind and storm slab layers, especially in the north zone, containing the Mt Baker area where heavier showers are expected.

Note that a refreezing 1/17 rain crust will continue to harden and may provide a bed surface for wind and storm slab avalanches on Friday.

Cascade West-North above treeline terrain will have very dangerous avalanche conditions Friday with large and potentially deadly wind and storm slabs. Travel in this area should be avoided until well after these slabs have time to stabilize. 

Elsewhere, building but shallower wind and storm slabs should maintain dangerous avalanche conditions. Storm slabs may form quickly and become sensitive to human triggering, especially in those areas receiving the greatest amounts of new snow (more than about 8" of new snow accumulated) and higher snowfall rates (extended periods of more than about 2" per hour). 

Conservative terrain choices will be essential in most areas, especially higher terrain and wind exposed terrain. Best to travel in wind sheltered, lower elevation terrain well away from steep open slopes until this new storm snow stabilizes. 

Lower snowfall amounts anticipated in the Cascade Passes will make storm slab less massive/reactive and wind slabs generally smaller, reducing danger relative to other areas.

 

No Corresponding Mountain Weather Forecast Available

USE AT YOUR OWN RISK

This Backcountry Avalanche Forecast is provided in conjunction with the US Forest Service, and is intended for personal and recreational purposes only. Safe backcountry travel requires preparation and planning, and this information may be used for planning purposes but does not provide all the information necessary for backcountry travel. Advanced avalanche education is strongly encouraged.

The user acknowledges that it is impossible to accurately predict natural events such as avalanches in every instance, and the accuracy or reliability of the data provided here is not guaranteed in any way. This forecast describes general avalanche conditions and local variations will always occur. This forecast expires 24 hours after the posted time unless noted otherwise.