Friday December 25, 2020

Sunday December 27, 2020
Saturday December 26, 2020
Friday December 25, 2020
Confidence: High - Many days of field data and weather models in agreement

Main Concerns

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

Travel & Terrain Advice

Significant amounts of new snow will fall Friday and Saturday so avoid loaded slopes during this time. It will be a great time to stick to low angled terrain or play amongst the trees. Wind loaded slopes on N to W aspects will be particularly dangerous.

Avalanche Summary

No new avalanches have been reported in the past couple days

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.

Avalanche Problems

Wind Slab

The Christmas snow will certainly be transported by strong SE to SW winds. This transport will load NW to NE lee slopes and create a significant wind slab issue. Last Monday’s storm stripped NW to NE slopes down to an old rain crust along the ridgetops, so our new snow will have a difficult time bonding to this old firm and slippery surface.

Location: All elevations on NW to NE slopes, especially near ridge top.

Likelihood of triggering: Natural avalanches are likely and these slabs will very likely be triggered by human activity.

Potential size: size one to size two.

Storm Slab

Significant new snow will fall Friday and Saturday creating the potential for storm slab avalanche activity. As the snow gets deeper and deeper the hazard will increase.

Location: All aspects in the alpine and treeline elevation bands.

Likelihood of triggering: Natural avalanches are possible and human triggered avalanches are likely.

Potential size: size one to two.

Loose Dry

As the storm matures cools and winds ease off, loose dry powder snow will cap this new blanket of white magic. This loose dry snow has the potential to slide in the form of loose dry avalanches.

Location: All aspects in the alpine and treeline.

Likelihood of triggering: Natural avalanches are likely and human triggered slides are very likely.

Potential size: size one to one and a half

Snowpack Summary

No new snow has fallen since the last bulletin came out. The weather since Monday has also left us with very variable surface conditions which the new snow, forecast for Friday and Saturday, will land on. Luckily the new snow comes in a bit warm so it will have some ability to bond to the old surfaces. The storm also tapers off with colder temps, so we should be left with nice light dry snow over warmer dense snow (a right side up cake as we snow nerds call it). This layering set us up well for a somewhat more stable but still fun snowpack.

Snowpack Details

SurfaceThin sun crust on solar slopes. ridgetop windward stripped down to old crust, lees small windslabs. powder in the shade
UpperStorm snow from Mondays event (one shear layer noted in tests) with a few thin decaying rain crusts below.
MidWell settled old snow with a beefy crust from that warm spell we had.
LowerWell settled

Past Weather

No new snow has fallen since last Monday. Winds have been moderate to strong from the SE and some snow transport has been seen loading on to N to W slopes at treeline and alpine elevations. Luckily temps did not get as high as the weather models had predicted so we are not cursed with a very nasty widespread melt freeze crust.

Weather Forecast

Santa brings a snow storm to the mountains for everyone!!! Significant new snow will begin to fall early Friday (Christmas) morning and will slowly taper off by Sunday. The storm comes in warm and leaves cold. Southern regions may even see the first bit of precipitation in the form of rain or a rain snow mix but it will soon change over to snow. Winds at the beginning of this storm will be high, but will also taper off as the storm travels through. Same with temperatures… warm getting colder.

Friday: 10 to 25 cm of snow, Strong easing to moderate SE to SW winds, Temps for 1500 m +2 to -1, Freezing levels 1800 to 850 m.

Saturday: 5 to 15 cm of snow, Strong to moderate SE to SW winds, Temps for 1500 m -1 to -5, Freezing levels 1000 to 900 m.

Sunday: 3 to 10 cm of snow, Moderate to light variable direction winds, Temps for 1500 m +1 to -4, Freezing levels 1200 to 600 m.

Posted on Friday December 25, 2020 by Bill Phipps

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