Bottom line: Two strong and very wet systems will hit the area (Early Monday, and again on Tuesday). Expect dangerous avalanche conditions both days, with large natural avalanches likely. Avoid all avalanche terrain during this time, including lower runout zones in valley bottoms. Total new snowfall of 24-48" is likely above 3000ft by Tuesday night.
Problem #1: Storm Snow:
Location: ALL aspects above 1500ft, especially wind loaded slopes.
Heavy snow is falling Monday, adding up to 12-20" above 1500ft. Strong SE winds are whipping the snow into fresh storm slabs, and rising temperatures mean the new snow is falling upside-down (weak underneath and slabby on top). It''s the perfect recipe for unstable snow. Storm slabs could be anywhere from 1-2 feet thick. There may be a break in the weather Monday afternoon, but the upper snowpack will still be quite unstable. As more heavy snow comes in Tuesday, dangerous avalanche conditions will continue. On isolated slopes, heavy wind loading may overload a lingering layer of facets over 1m deep, causing very large avalanches.
Problem #2: Wet Avalanches:
Location: all aspects below 3500ft, steeper than 30 degrees.
This storm will bring increasing temperatures and snow levels rising to 3000ft, possibly higher, Monday and Tuesday. As heavy rain begins falling on our snowpack, natural wet slabs and nasty wet-loose slides will begin in steep terrain. They will funnel into gullies and terrain traps and could build up quite deep. Make sure you're not on or beneath steep terrain during this period of rain-on-snow.
We received some recent reports of fresh natural and human triggered wind slab avalanches to size 2 or 3, over the last few days. These were occurring on slopes that are lee to the northwest winds that blew over the last several days, where active wind loading was occurring.
Above: Human-Triggered D1.5 hard slab avalanche on the Chilkat Pass, from 12-23-2018. E aspect, crown was about 1 foot deep.
Isolated D2-D3 naturals ran during the storm last week, on wind loaded and cross loaded aspects. Crown depths were around 1 meter, running on facets above a rain crust.
Natural D3 avalanche from the big storm last week. Chilkat Pass zone, cross-loaded NE aspect at ~4500ft. 2018-12-21
Monday-Tuesday will feature two strong and wet storms bringing heavy accumulations and snow levels rising to near 3000ft. Total new precipitation amounts of 2-4" are likely by Wednesday (meaning 24-48" of new snow above 3000ft, 6-24" below that level). On Wednesday, snow levels will drop to sea level and light-moderate snow accumulations should continue.
( *star means meteorological estimate )
If you get out riding, please send in an observation!
Do a rescue practice with your partners. Always carry a beacon, shovel, and probe, and KNOW HOW TO USE THEM. Come to our FREE backcountry skills workshop on January 10th (see flyer below).
Practice good risk management, which means only expose one person at a time to slopes 30 degrees and steeper, make group communication and unanimous decision making a priority, and choose your terrain wisely: eliminating unnecessary exposure and planning out your safe zones and escape routes.
Two strong and very wet systems will hit the area (Early Monday, and again on Tuesday). Expect dangerous avalanche conditions with large natural avalanches likely. Avoid all avalanche terrain during this time, including lower runout zones in valley bottoms.
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