This Bulletin Valid Until: Friday December 22nd, 2017 @ 6 pm. 

Main Concerns: (Avalanche problems)

Storm Slab -  Snowfall amounts early this week in the range of 10-40 cm overlie a melt freeze crust on all aspects and elevations. This new snow and crust combination may form storm slabs on all aspects and elevations. Natural avalanches are possible in the wake of this new load and human triggering is likely. These avalanches have the potential to be from small (size 1) to large (size 2+).

Travel/Terrain Advice: Avoid steep convex rolls and be aware of recent reverse wind loading especially at ridge top. Take note of the depth of new snow over the old crust surface and if that snow is sticking to it. Recognize the potential for wide slab propagation and utilize safe zones and minimize exposure of suspect slopes to one at a time. 

Past Weather: A series of low pressure systems peaking in intensity on Tuesday have brought moderate snowfall to the Island mountains. Sunday saw elevated freezing levels and rain to about 1400 m followed by dropping freezing levels and temperatures. The bulk of new snow has come Tuesday in a NW to NE flow which is not the common pattern.

Avalanche Summary: On Tuesday numerous small soft storm slabs were reported at treeline on NW through NE aspects on all sufficiently steep slopes in the Mount Washington area. These avalanches were touchy to very touchy to ski cutting and were failing on the old crust that was buried 20-40 cm. One natural slab avalanche was observed at treeline on a SW aspect also failing at the crust. 

Snow Pack Description:  

Surface - 30-40 cm of low density snow with variable distribution due to moderate to strong NW through NE winds overlies the old crust. Some windward slopes have been stripped down to the crust. Expect wind loaded pockets on lee slopes up to 50-60 cm deep.

Upper - 40-60 cm of new snow load is now on the old crust surface and is bonding poorly. Some sugary snow has been observed below the crust especially on northern aspects in the alpine.

Mid - Well settled.

Lower - Well settled.

Weather Forecast: Another high pressure system begins to build off the Pacific coast and will bring clearing skies, cooling temperatures and dropping freezing levels. This ridge should prove to be a clean ridge, meaning no low level clouds and fog, just cold and clear. Minimal precipitation in the foreseeable future.

Wed - No new precipitation. Winds 30-40 km/h north veering to 20-15 northwest.

Freezing levels of 0-850 m

Thu - Trace amounts of snow on the north and east Island. Winds from the west 10-20 km/h.     

Freezing levels of 0-950 m

Fri - No new precipitation.  Winds northeast 15-40 km/h.

Freezing levels of 0-850 m

Prepared by Dan Goodwin