Friday January 19, 2018

Sunday January 21, 2018
Saturday January 20, 2018
Friday January 19, 2018
Confidence: High - Significant storm system confirmed to continue with weather models, lots of field data gathered.

Main Concerns

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

Travel & Terrain Advice

Travel in any avalanche terrain is NOT recommended when the hazard rating is HIGH or above. Stick to in-bounds controlled terrain or low angled slopes in forested areas with only small openings. Avoid large wind loaded open slopes on north west-north east aspects at all elevation bands. Travel will be very difficult due to new snowfall accumulations so give yourself extra time to be home before dark and bring emergency overnight gear just in case. Be cautious of what is above you, do not to expose yourself to overhead large avalanche terrain. Now is not the time to ride the big lines!

Avalanche Summary

Control work on Mt Washington produced numerous size 1-1.5 soft slabs and a few size 2 with explosives. Ski cutting produced a few soft slabs and numerous loose dry avalanches.

Avalanche Problems

Wind Slab

Very high to strong south east to south west winds will transport snow to lee aspects and will form wind slabs. These slabs will very likely create avalanches both with human and natural triggering and could be up to size 3. These slabs will form in all elevations bands where ever the wind can access. Remember, a rule of thumb is that the wind can move and deposit 3-5 times the amount of snowfall to lee aspects, so…. 30 cm of new snow could mean 90-150 cm of snow deposited to form wind slabs. That is a deep and big avalanche!

Storm Slab

Large quantities of new snow will fall on all aspects and will very likely to produce storm slabs. These slabs have a high potential to trigger both naturally and with human activity. They will be widespread in the alpine and treeline and in specific/open terrain below treeline. Due to the volume of new snow these avalanches could be up to size 3.

Loose Dry

New low density snow will form loose dry avalanches on all elevations and aspects in steep terrain. Triggering is certain with human activity and very likely with natural triggering up to size 1.5.

Snowpack Summary

Significant (OK, LARGE) quantities of new snow have fallen during the previous forecast period and will continue to fall. This new snow seams to be bonding well to the old crust but shears or failures have been noted within the new storm snow.

Snowpack Details

SurfaceWidespread new snow with wind slabs on lee slopes. Some isolated zones of exposed crust at ridge top
UpperNew snow gaining in density as it gets lower. Some storm shears noted in tests. Bonding well to the old buried crust
MidWell settled
LowerWell Settled

Past Weather

Significant new snow for the entire forecast area. Approx 40 cm to the north, 80 cm in the east and a huge 150+ cm in the west. A short temperature spike Wednesday warmed the upper snow pack. This warming helped bond the new snow to the old crust below and has now cooled and tightened up. Now, more snow has fallen on top with a few density changes/shears, but seams to be relatively stable.

Weather Forecast

More, More and More new snow! Another 80 cm-140 cm are forecast to fall during this forecast period/over the weekend, with a large load Saturday night into Sunday morning. This new snow will be accompanied by strong south east-south west winds, so expect significant snow transport. Temperatures will continue to cool so the snow will be amazing.

Fri - 18-40 cm of new snowfall, strong south east to south west winds, freezing levels 900 m-1200 m

Saturday - 15-40 cm of new snowfall, strong south east to south west winds, freezing levels 700-1000m

Sunday - 40-60 cm of new snowfall, very strong to strong south east winds dropping to moderate, freezing levels 700-1000m

Posted on Friday January 19, 2018 by Bill Phipps

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