Monday December 28, 2020

Wednesday December 30, 2020
Tuesday December 29, 2020
Monday December 28, 2020
Confidence: High - Weather models in agreement and good field data.

Main Concerns

Loose Wet, Storm Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Watch steep direct solar slopes if things start to warm up when the sun comes out. The heat may increase the chance of loose wet avalanches. Pinwheels and tree bombs are a hint its getting dangerous.

Watch for shooting cracks in the snow as this is a significant sign of a weak dangerous layer underfoot.

Avoid all avalanche terrain when the rating is high for an elevation band and travel when the rating is considerable is certainly on the sketchy side of things as well. A good old saying is add the words “chance of death” after the danger/hazard rating word. As in “considerable chance of death”….

Avalanche Summary

We would like to remind folks to send in their snow, avalanche and weather info directly to this bulletin. Please send your snow stories to forecaster@islandavalanchebulletin.com as your info greatly helps us write more accurate bulletins for everyone’s safety. It does not have to be technical snow terms… just write in your own words what you saw and how it all went out there. The great news is that, if you report to us directly, you will often get contacted by our on duty forecaster to discuss your info so it’s a great two way learning experience.

Many thanks to those of you that did send us info. Cliff Umpleby, Kai McGrady, Connor Silverton, Faelan Prentice and of course Mt Washington Ski Patrol.

There was a lot of avalanche action on the ski hill the past three days as the Mount Washington zone saw the most new snowfall for the island . Patrol reported a few avalanches from size one and a half to size two with explosives and numerous size ones with ski cutting. There were no reports of avalanche activity from other sources.

Avalanche Problems

Loose Wet

As the sun tickles steep solar slopes later in the day Monday or when a rain snow mix rolls in at lower warmer elevations during late Tuesday night/Wednesdays storm event there will be a potential for wet loose avalanches.

Location: Monday steep solar (SE to SW aspects) affected slopes at all elevations, Tuesday night/Wednesday below treeline all aspects.

Likelihood: possible with natural triggering and likely to human activities.

Potential size: size one to two.

Storm Slab

As the next storm rolls in it will come with substantial new snowfall. This snow will create storm slab avalanche conditions. Potentially falling on a melt freeze crust, forming Monday Tuesday, these storm slabs will be touchy and raring to roll downhill.

Location: all aspects and elevations (below treeline, treeline and alpine) especially NE to NW sides where the wind will transport even more snow to.

Likelihood: triggering will be likely for naturally occurring avalanches and very likely with human triggers.

Potential size: size one to size two, with possible size threes in the alpine or alpine like features found at treeline).

Snowpack Summary

Well the past three days did not disappoint for new x mas snowfall. There was an average of 20 to 30 cm of new snow for most zones with Mt Washington getting a whopping 50 cm. The north got the least with Cain hitting 11 cm.

Snowpack Details

SurfaceA bit of snow Sunday night over a thin crust at higher elevations and lower down moist snow capping the x mas snow.
UpperNew x mas storm snow from the past three days 11 cm all the way to 50 cm with some signs of weak layers within
MidWell settled with some old crusts
LowerWell settled

Past Weather

Santa brought us the great gift of snow. Three big storms have significantly increased our snowpack depth. Temperatures hovered around the 0 to -1 degree mark so it was not blower powder, but hey we will take it! Strong winds came from the SW to SE so the alpine and ridgetops have been affected, but down in the trees things have been pretty darn fantastic.

Weather Forecast

Things settle down for a couple days (Monday Tuesday), but then the next big storm system hits starting later in the day/early evening Tuesday. We may see some sunny breaks Monday into early Tuesday with mild temps during the day and a clear cold at night in between. This may create a crust on the snow surface which will be a potential sliding layer for the snow walloping coming Tuesday night into Wednesday.

Monday: a trace to 10 cm of new snow Sunday night into Monday morning then clearing midday , winds light from variable directions, temps for 1500 m -1 to +1, freezing level 1000 m dropping to sea level in the evening.

Tuesday: a trace to no new snow, winds light S increasing to strong SE to SW as the day goes on, temps for 1500 m +2 to -3, freezing level 900 to 200 m.

Wednesday: 30 to 50 mm of precip with all falling as snow at upper elevations and a potential for a rain snow mix for lower (1 mm of precip is equal to 1 mm of rain, 1 mm of precip in the form of snow is approx 1 cm of snow. So 30 to 50 mm could be a heck of a lot of new snow! winds strong SE to SW, temps for 1500 m +2 to -1, freezing level 1300 to 700 m.

Posted on Monday December 28, 2020 by Bill Phipps

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