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RegisterJan 15th, 2015–Jan 16th, 2015
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New storm and wind slab mainly on lee aspects may bond poorly to the existing snow surface, especially if overlying a surface hoar layer present in many areas. Watch for unstable slab layers and avoid steep lee slopes that may have received wind transported recent snow, especially steep NW thru NE facing slopes.
A period of light to moderate precipitation expected overnight should build storm slab layers, especially near treeline and above.
New storm and wind slab should be possible Friday, especially near and above treeline. Strong winds overnight Thursday will have likely built unstable slab layers on NW-NE facing slopes, mainly below ridges.
Light and decreasing snow showers are expected through the day Friday with a cooling trend. This should allow for slowly improving avalanche conditions as storm layers begin to settle.
On backcountry travel safety note, watch for terrain hazards (exposed rocks, trees, streams, etc.) at lower elevations and on wind scoured aspects.
An approaching storm will move across the area Thursday night and early Friday, changing the recent snowscape, from one dominated by crust layers, to one with some fresh snow. The last storm arrived on January 4th, depositing about 6-12 inches of snowfall, followed by warming and rain on the 5th. This caused an avalanche cycle east of the crest. In the northeast Cascades at higher elevations more of the precipitation fell as snow before precipitation ended than elsewhere.
The latest high pressure has been marked by warm temperatures and sunshine in most alpine zones with cooler and sometimes foggy conditions in the valleys and to near treeline along the east slopes.
NWAC pro-observer Tom C. northwest of Blewett Pass Thursday, found widespread surface hoar up to 5mm on most aspects and elevations up to 5400 ft. The persisted facet layer found on Jove Peak on Wednesday was also found at 85 cm Thursday, but it also was unreactive to snowpit tests. The stronger crust layers above should be solid enough to support a fairly significant new snow load, so it is unlikely to be a layer involved in future slides, at least in the near term.
However, if the surface hoar layer becomes buried, that is a different story. Watch and test for this potential layer in areas where significant new snow accumulates and storm slab layers develop.