Avalanche Forecast

New shallow wind slab may from on lee N thru SE aspects, mainly in the afternoon on Tuesday as a weak low pressure system heads into southern Washington and northern Oregon.  If precipitation rates of the new snow accumulation becomes heavy enough Tuesday afternoon, watch for new snow instabilities late in the day. 

 

 

 

A front crossed the Northwest Thursday afternoon and night. Temperatures began quite warm and cooled during the storm. This initially produced rain or wet snow that gradually transitioned to snow at lower elevations. New snow amounts varied from north to south and with elevation. Upper elevations in the north received about 20-30 cm (8-12 inches) of new snow with lower elevations and areas in the south getting about 10-20 cm (4-8 inches).

Sunny weather with increasingly warm temperatures were experienced over the weekend except where easterly flow maintained locally cooler temperatures near the passes. Increasing mid and high clouds on Monday a bit of SW ridgetop wind likely stunted any significant softening of solar aspects.

Reports indicate mostly favorable profiles in the new snow and good bonding of the most recent storm snow to older wet snow. The mid and base pack mostly consists of stable layers of crusts and rounding or melt forms due to warm periods in late December and early January.

The exception was where the new snow bonded poorly to a slick rain crust. On this past Saturday sensitive storm and wind slab released in at least 2 different human triggered incidents.  A climber triggered 2 separate slides and was caught in a 1 foot storm or wind slab in the east facing bowl below Chair Peak near Snoqualmie Pass at about 5500'.  The climber was not seriously injured.

A photo of the Chair Peak slab crown.

A skier also triggered but was not caught by a 1-1.5 foot storm or wind slab on a south facing slope on Mt Herman near the Mt Baker ski area at about 5700 feet. The bonds here may not have been as good between the recent and old snow with the old crusted snow acting as a bed surface. Sunshine may have helped to activate this slope.

Small loose wet snow avalanches were also reported on solar aspects over the weekend, releasing easily on the slick underlying crust.

There were widespread reports of surface hoar the last two mornings with the clear cool nights from the lower elevations of the cooler Cascade passes and on shaded aspects throughout the west slopes. Watch for this layer to become reactive if it is not destroyed with the next incoming system, mainly on more sheltered and shaded slopes in higher terrain.   

Surface Hoar photo taken 1/05/14 at Snoqualmie Pass snow study plot, courtesy John Stimberis WSDOT

There will be less danger in areas that received less recent snow such as Hurricane Ridge and Crystal Mountain. The avalanche danger will continue to be low at lower elevations due to less recent snow and a low snowpack.