This Bulletin Valid Until: Friday January 19, 2018 @ 6 pm.
Main Concerns: (Avalanche problems)
Storm slab- Significant quantities of new snow will fall this forecast period. This new snow will form slabs that will be touchy as their bond to the old crust from the previous period will be poor. These slabs will very likely produce avalanches, both naturally triggered and human, up to size 3 and will be found on all aspects and elevations.
Wind slab- The new snow will be accompanied by strong south east winds. These winds will certainly form slabs on north to west slopes in the alpine, treeline and open zones below treeline. These slabs will very likely trigger naturally and with human activity and have the potential to be up to size 3.
Wet slab- A short lived spike in temperature and freezing level Wednesday afternoon till early evening, may possibly bring rain to the prior new snowfall. This additional loading could cause the release of wet slab avalanches on all aspects and at all elevations. These slabs will be touchy and will potentially be triggered both naturally and with human loads and could be up to size 2.
Travel/Terrain Advice: Travel in any avalanche terrain when the hazard rating is high is strongly not recommended. Expect large avalanches in many areas and very large avalanches in specific areas. Still want to take advantage of the new powder.... Stay at the ski resorts where control work will reduce the danger or ski those low angled tree lines you love so much. Be wary of the potential for the temperature spike Wednesday afternoon. If taking observations of the snowpack, the bond of the new snow to the old will be a main concern. Be patient with your terrain choices and give it time to settle down and out before you turn the Rad on...
Past Weather: Warm temps and high freezing levels did not drop until later in the day Tuesday. Light to moderate amounts of new snow fall began and tests showed a very poor bond to the old crust formed in the treeline and above.
Avalanche Summary: Late Tuesday's new snow has already shown avalanche results with the release of small windslabs at treeline elevations. Ski cutting at the end of the day on north to west aspects in the upper treeline at Mt Washington (by avalanche control teams) easily triggered small windslabs running on the old crust up to size 1.
Snow Pack Description:
Surface - The new snow has already begun to accumulate and will continue to do so in significant quantities this forecast period. Moderate (forecast to increase to strong) winds are building hardened windslabs on lee (north-west) slopes.
Upper - The moist snow surface (from prior warm temps and rain) cooled by winds and dropping temps formed a thin melt freeze crust that remained intact on all aspects (except some direct solar below treeline terrain). This crust is now buried by the new falling snow and there is a very weak bond between them.
Mid - Well settled and gaining strength
Lower - Well settled.
Weather Forecast: Winter is finally here? La Nina? Who knows, but it sure looks like great skiing etc. ahead. Significant new snow will fall over the next three days with strong south east winds. A short lived temperature spike Wednesday afternoon in to early evening may put a bit of a damper on things, but they will soon turn back into a skier, snowboarder, snowshoe, snowmobile dream.
Wed - 10-30 mm of rain and 10-40 cm of snow. Winds moderate rising to strong from the south east.
Freezing levels of 1000 m rising to 2500 m during the spike then dropping to 800 m
Thurs - 20-50 cm of snow. Winds strong south east.
Freezing levels of 800-1000 m
Fri - 20-40 cm of snow and 5 mm of rain. Winds moderate to light south east.
Freezing levels of 750-1200 m
Prepared by Bill Phipps