This Bulletin Valid Until: Friday January 12, 2018 @ 6 pm. 

Main Concerns: (Avalanche problems)

Storm slab - New snow through the forecast period with the bulk falling Wednesday night into Thursday will create storm slabs up to size 1 in the alpine and open exposed treeline. These slabs will be possibly triggered by human activity and will be on all aspects.  

Wind slab -  Wednesday/Thursdays storm will come in with moderate south east winds.  These winds will create wind slabs in the alpine, open exposed treeline, and on lee sides of ridge top features.  Found in specific terrain, these slabs will be likely-possibly triggered by human activity and have the potential to be up to size 2

Deep persistent slab - Significant new snow has fallen since January 7th on a rain crust formed on the 6th.  The bond of the new snow to this crust, and a layer just above it, have shown in tests to be weak.  Moderate snow fall this Wednesday night into Thursday might just be the additional load to trigger down to this layer and/or  other avalanches running above this layer have the potential to "step down" to this layer, vastly increasing the avalanche size. This deep layer will be unlikely to initiate, but possible in areas of thinner snowpack depths (like near ridge top or around rocky features) or with a large natural triggers.  They would be found in the lower alpine and treeline and have the potential to be up to size 2-2.5

Travel/Terrain Advice:  Avoid steep loaded slopes and features with north-west aspects that gather wind transported snow.  Watch new snowfall amounts over Wednesday night and use careful route finding and cautious decision making after the storm cycle.  Snowpack evaluation/tests Thursday will be important information to gather if traveling in more challenging terrain.          

Past Weather:  Strong (up to 70k mph) winds from the south-east accompanied the new snowfall (up to 15cm) Sunday.  Monday a spike in the freezing level  (up to 1300m) increased temperatures and left a thin melt freeze crust on solar aspects after it pasted, in all but the alpine elevations.  Late Monday into Tuesday another wave of new snow fell on the hills bringing anywhere from 12-20cms of fresh.   

Avalanche Summary: Sunday avalanche control on Mt Washington saw a few very soft slab-loose avalanches on north west slopes in the treeline with ski cutting and explosives.  Ski cutting in other near ski hill terrain produced numerous very small wind slab avalanches on convex unsupported ridge top features.  A skier accidental in out of bounds terrain at Mt Cain (west bowl) was also was reported in the size 1.5-2 range (see incident reports section for more details).  Monday ,once visibility improved, several small naturally triggered point releases were seen from steep north aspects at treeline on the back of Mount Washington (most probably running prior during Sundays storm) and one small wet slab size 1 was noted by skiers on Mt Elma ,in paradise meadows, on a open north aspect unsupported convex roll below treeline (associated with the 1300m freezing level spike no doubt).   So an active three days for avalanches for the island.     

Snow Pack Description:

Surface - Preserved new snow in sheltered zones in the treeline and below treeline elevations.  Alpine and exposed treeline have stiffer wind pressed snow and ridge tops have some isolated zones of wind stripped exposed crust.  

Upper - New snow everywhere with a thin non-supportive crust on solar aspects, approximately 12-20 cm down on below treeline and treeline terrain from Monday's warm spike.  Sunday's new snow (15-5cm) has created wind slabs (now buried) on north to west aspects in the alpine and treeline.  All this new load is sitting on the January 7th rain crust and has shown significant weakness and failures in tests.  

Mid - The new snow and crust buried on Jan 7th is now bridging and almost eliminating concerns surrounding the mid Dec and mid Nov crusts. The moist mid snowpack seams very stable producing only hard results in tests on the Dec crust.

Lower - Well settled.

Weather Forecast:   Light snowfall with cloudy skies and cold temperatures Wednesday. Fallowed (Thursday) by a new storm system via moderate southeast winds, bringing snowfall amounts from 5-15cm in the north to 15-25cm for the west coast and 10-15cm for the east. Light snow at first Friday and then a trend (unfortunately) toward warming and high freezing levels for the weekend. 

Wed - 1-5 cm of new snow. Winds light south east to south west.

Freezing levels of 140-900 m

Thurs -   5-25 cm of snow.  Winds moderate south east. 

Freezing levels of  400-1000m

Fri - 2-7 cm of new snow. Winds light west to moderate south.

Freezing levels of 0-1250 m

Prepared by Bill Phipps