Monday March 15, 2021

Wednesday March 17, 2021
Tuesday March 16, 2021
Monday March 15, 2021
Confidence: Moderate - Uncertainty with extend of wind distribution of storm snow , numerous reports, numerous forecaster field observations and good weather model agreement.

Main Concerns

Cornice Fall, Wind Slab, Storm Slab - view Avalanche Problems for detailed information.

Travel & Terrain Advice

Please respect the avalanche/patrol team and workforce at Mount Washington, at no time is uphill travel or unsanctioned use of the private property permitted.

Practice patience and allow time for new storm instabilities to stabilize prior to committing to any steep terrain.

Plan routes and choose terrain that is low angle and supportive as you begin to venture into unmodified and uncontrolled snowpack and terrain.

Identify and avoid travel either above or below cornice features.

Adjust travel plans to ensure avoidance of solar aspects during warming and when the sun is out.

Avalanche Summary

Please respect the avalanche/patrol team and workforce at Mount Washington, at no time is uphill travel or unsanctioned use of the private property permitted.

Mount Washington Avalanche control teams report triggering on all aspects between 1500 and 1300 meters numerous size 1 to 1.5 utilizing ski cuts and explosives, as well a couple of size 2 avalanches. These avalanches when trigger propagated widely and ran full path with good entrainment of the mass. These avalanches where all within the new storm snow (45cm total) and on terrain greater than 30 degrees.

Guiding operations reports a number of size 2 skier accidental avalanches on north and north west terrain in the backcountry outside of the ski area boundary. No details on elevation, involvement or loss of gear.

Avalanche Problems

Cornice Fall

Very large cornices exist and continued snowfall, wind and high humidity continue to promote cornice growth. Cornice failures have the potential to over load the snowpack and trigger both new snow instabilities as well deeper instabilities. Expect the new growth to be fragile and when temperatures and freezing levels rise become suspected triggers in bigger avalanche events.

Location: North thru to West aspects at ridges top in the Alpine and Tree line.

Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers. Natural avalanches are possible to likely.

Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3 .

Wind Slab

This new avalanche problem will initially be very sensitive to triggering and will slowly begin to settle and stabilize over the forecast period. Found on predominantly North aspects. This avalanche problem was formed during the past storms strong south winds and overlies in isolated Alpine terrain surface hoar. All other surfaces were warm and moist.

Location: North East thru to North West aspects and found in both the Alpine and Tree line.

Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers. Natural avalanches are possible to likely.

Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3 .

Storm Slab

This new avalanche problem will initially be very sensitive to triggering and will slowly begin to settle and stabilize over the forecast period. On isolated Alpine terrain expect this new snow to have buried surface hoar. On solar aspects, expect the storm snow to overlie a melt freeze crust and is likely to become more reactive to triggering during daytime warming and solar effect.

Location: All aspects, Alpine and Tree line. Below tree line hazard is from above.

Possibility: Triggering of this avalanche problem is likely to very likely from light loads such as skiers. Natural avalanches are possible to likely.

Size: If triggered expect these avalanches to be large size 2, on isolated terrain features very large, size 3.

Snowpack Summary

New storm snow of up to 60 cm arrived on Sunday and this overlies a variety of surfaces. On isolated north aspects in the Alpine, surface hoar and on solar aspects a crust. 1500 meters and below, this new storm snow overlies a warm and moist surface.

The upper snowpack continues to settle and a faceted decomposing crust combination can be found down 100 to 200 cm. This crust is producing sudden planar results during moderate testing and with a very large trigger such as a cornice fall could be triggered.

The persistent slab from February is now down over 250 centimeters and is dormant and currently non reactive to testing.

Below the snowpack is dense and well settled.

Snowpack Details

SurfaceNew storm snow between 40 to 60 cm.
UpperSettled snow between 100 and 200 centimeters overlies a faceted and decomposing crust..
MidOld unreactive crusts, overall dense and well settled.
LowerWell settled and dense.

Past Weather

A strong cold front passed over the forecast area Sunday, this system delivered 60 cm on the northwestern zones and 40 to 50 cm to the mid and south zones. In the wake of the storm temperatures cooled and winds subsided.

Weather Forecast

Predominantly clear conditions with daytime warming and sun. Expect warming to increase daily throughout the forecast period. Wednesday expect the northern zone of the forecast area to see precipitation and increasing South east wind with the southern zones receiving trace amounts of precipitation.

Monday: No new precipitation Winds Strong backing to Light from the North West , Freezing levels at sea level rising during the daytime to 600 meters. Temps at 1500 meters up to 3 degrees.

Tuesday: Trace amounts of snow, Winds light to moderate from the South East, Freezing levels at sea level rising during the daytime to 700 meters. Temps at 1500 meters up to 4 degrees.

Wednesday: 1 to 5 cm , Winds Moderate to Strong from the South East, Freezing levels 600 meters with a daytime a high of 1000 meters. Temps at 1500 meters up to 4 degrees.

Posted on Sunday March 14, 2021 by Jesse Percival

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