Friday March 2, 2018

Sunday March 4, 2018
Saturday March 3, 2018
Friday March 2, 2018
Confidence: High - Lots of field data gathered and weather models in good agreement

Main Concerns

Wind Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

With the significant wind events over the past two days (Wednesday and Thursday), avoid wind loaded slopes. The majority of the winds have been from the SE so N-W slopes are the most prone. However recent variability in wind directions means that wind slabs may lurk under the fresh snow in unexpected places, so be wary. Watch for signs of instability like shooting cracks, whumphing and hollow drum like sounds/feeling. Warming Friday may make triggering avalanches more likely, so watch exposure as the temps climb.

Avalanche Summary

Avalanche control on Mt Washington has produced a few size 2 and numerous size 1 avalanches with explosive control and widespread loose sloughing with ski cutting over the past two days. Natural activity up to size 2 has also been reported by the public.

Avalanche Problems

Wind Slab

Two howling days have significantly moved the new snow around and created widespread wind slabs in all elevation bands. The majority of the wind slabs are found on N-W aspects, but some variability in the wind means we can find slabs lurking on all aspects. These slabs may possible trigger naturally (esp. in the alpine and open tree line where winds are more pronounced) and are likely to trigger with human activity up to size 2 (ie enough to injure, hurt, kill and or bury a person). These slabs will begin to settle down as we move forward in the forecast period, reducing their likelihood to trigger.

Snowpack Summary

Approximately 20 cm of new snow has fallen over the past two days with a layer (1-3 cm) of graupel (the snow equivalent of hail) in some regions just below the surface. Significant redistribution by variable but mainly SE winds have created wind slabs on lee slopes and also pressed snow on windward aspects. The new snow has been bonding moderately well to the Valentines day crust below, even on the previously rock hard ice/crust exposed ridge-line zones. The Valentines crust is still extremely thick and supportive. The mid and lower snowpack is well settled and capped by the crust.

Snowpack Details

Surfacewidespread wind slab 20-60 cm (with a few very loaded areas up to 90cm)
Uppernew snow (20 cm) gaining in density as it gets deeper
Midthick, thick Valentines day crust, over well settled snow
Lowerwell settled

Past Weather

“Mile after mile in the fresh morning breeze.” Yes another Dr Seuss quote… it is his birthday this Friday after all. Well the winds have been certainly Fresh! Both Wednesday and Thursday saw Strong to Very strong variable direction winds in the east and west regions, but only strong to moderate winds to the north. The 20 cm of new snow has been pushed around and packed in. Temps have remained cool and freezing levels have stayed low.

Weather Forecast

Things will settle down as we enter the weekend with only a slight weak disturbance Friday. Should be a great weekend to get out and play.

Friday - 0 to 5 cm of new snow, moderate N winds easing to light variable, slight temps spike to -1 then dropping to -4, freezing levels near sea level then rising to 1000 m (that’s a big gain in a short time frame that will affect the snow pack and stability).

Saturday - 0 to a trace of new snow, light variable winds, temps -2 to -4, freezing level 100 to 1000 m.

Sunday - 0 to 2 cm of new snow, light variable to SW winds, cooling off to -4 to -7, freezing level 73 to 900 m.

Posted on Friday March 2, 2018 by Bill Phipps

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