Friday December 21, 2018

Friday December 21, 2018
Saturday December 22, 2018
Sunday December 23, 2018
Confidence: Low - Limited field observations from northern and western areas

Main Concerns

Storm Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Recent sustained strong winds will have created large fragile cornices on ridge tops, give them a wide berth and use caution when travelling above them. Be aware of wind loaded areas and watch for signs of instability including cracking, whumpfing and evidence of recent avalanches. Conditions will vary greatly with changes in elevation.

Avalanche Summary

Explosive testing Wednesday at Mount Washington produced several small (size 1-1.5) storm slab avalanches in lee terrain at treeline (NW through NE aspect). These avalanches were approximately 15-25 cm deep and failing only in the recent wind loaded snow. A few natural storm slab avalanches in the size 1 to 1.5 range were observed in the same previously controlled terrain during the height of the precipitation and warming of the significant storm event that took place on Thursday. These avalanches were also triggered in the new snow only with no signs of failure from deeper layers. Many small loose wet avalanches were also observed on Thursday on all aspects below treeline.

Avalanche Problems

Storm Slab

Continued wind and snow loading will very likely create storm slabs that could be reactive to light loads such as a skier. These avalanches may be large (size 2-3) and found on all aspects, especially at treeline and above with deepest and touchiest areas in the wind loaded alpine areas.

Snowpack Summary

Up to 80 cm of new storm snow fell during Thursday’s storm in alpine areas with much of that precipitation coming in the form of rain below 1500 m. Expect deep wind loaded areas above 1500 m and rain soaked upper snow below. Snow depths at treeline are in the 250 cm range with wind loaded areas in higher elevations well over 3 m.

Snowpack Details

SurfaceEither 60-80 cm of wind affected new snow or rain soaked depending on elevation
UpperLoose dry snow above 1400 m and 20-30 cm of moist snow below 1400 m
MidMultiple layers of rounding storm snow with varying densities
LowerWell settled

Past Weather

Sounding like a broken record. Another powerful and potent storm system with heavy precipitation, strong to extreme southerly winds and wildly fluctuating freezing levels have deposited more snow to the Island peaks. Lower elevations experienced significant rain events.

Weather Forecast

FRIDAY - 10-15 cm of accumulation with freezing levels around 650 m. Winds strong from the west veering to SE.

SATURDAY - 20-45 cm of accumulation with freezing levels around 750 m with the lower amounts for the north. Winds strong to extreme from the SE.

SUNDAY - 15-25 cm of accumulation with freezing levels around 1000 m. Winds strong from the SE veering to SW.

Posted on Friday December 21, 2018 by Dan Goodwin

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