Avoid all avalanche terrain. There may be a large natural avalanche cycle this weekend. Some slides could be quite large, reaching lower runout zones on valley bottoms.
We have a weak snowpack that has been steadily loaded over the last week. It has also been slowly warmed up over the last two weeks and we're starting to see large avalanches stepping down to deep layers. Heavy precipitation and warming this weekend will only exacerbate the persistent slab problem.
Problem #1: Storm Snow
Location: all aspects and elevations, but especially W-NW-N-NE aspects.
Heavy precipitation Friday night will let up a little Saturday. Up to 1" of new SWE is expected in this zone. Southeast winds will be strong.
On Wednesday night this area received around 1" of water-equivalent. This is on top of a similar amount that fell Sunday 3/10. The new storm snow is heavy, moist, slabby, and wind-affected. It sits over a layer of old facets about 60cm deep, under Sunday's snowfall. In any wind-affected terrain, expect the new snow to be forming tender soft slabs 30-60cm thick. Natural and Human-triggered avalanches are likely this weekend on slopes 30-degrees and steeper.
Problem #2: Persistent Slab
The heavy load of new snow is actively overloading these deeper weak layers, and step-down avalanches are likely.
Beneath the new/recent snow, we have two different persistent-slab dangers to watch out for: 1) old facet layers, and 2) buried surface hoar.
1) For the old-facets problem: Location: All aspects, at elevations above treeline where the snowpack is thin/windswept.
One concern is in areas of thin snowpack, where old facets (1-2mm) lurk underneath the wind slabs that sit 30-60cm deep. Our heavy load of new snow may activate these dormant layers. Pole probing can help you map out which slopes contain hard-over-soft layering, a sign of this persistent slab danger. Remote triggering is possible, so keep track of your group and manage your exposure carefully.
2) For Buried Surface Hoar: Location: ALL elevations, clearings in the trees, and specific slopes above treeline (mainly slopes sheltered from NW winds) where surface hoar formed over the last 3-4 weeks and wasn't blown away by NW winds.
There are areas of buried surface hoar lingering at one and three layers down (roughly 50-80cm deep). These dangerous weak layers will persist for several weeks until they can be crushed and flushed out by lots of heavy snowfall. Be sure to dig around in wind sheltered areas to look for "the thin grey line" and clean shears. Assume this weak layer to be present in wind-sheltered areas. Use extra caution in openings around treeline, and avoid wind-sheltered rollovers in the alpine.
Problem #3: Wet Avalanches
Location: Below 4500ft where temperatures have warmed above freezing and/or rain has fallen on recent snow.
The recent snow is wet and heavy. With warming temperatures today and continued rain-on-snow, wet-loose and wet-slab avalanches will be likely in steep terrain (30-degrees and up). Steer clear of any gullies or depressions where wet debris tends to funnel.
Natural and skier-triggered slides size D1-D2 were observed in low vis Thursday in the Lutak zone. Other observations have been limited. Sadly, there was an avalanche involvement at Mumford's (Lutak Zone), Wednesday 3/13 with one fatality.
Our zones have seen 15-36" of new snow in the last week (lowest amounts at the pass, highest in the Lutak zone). South winds have been howling out of the southeast. Periods of heavy Precipitation will continue Friday night and Sunday, with 1-3" of additional SWE and snow levels rising to 2000ft Saturday, and up to 4000ft Sunday.
Snow Depth [in]
Last 24-hr Snow/SWE [in]
Last 3-days Snow/SWE [in]
Today's Freezing Level [ft]
Next 24-hr Snow/SWE
10" / 0.80
22" / 1.80
2000 rising to 4000ft sunday
12" / 1.00 *
6" / 0.60
17" / 1.50
12" / 1.00 *
5" / 0.45
8" / 0.75 *
( *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.
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.
All avalanche terrain should be avoided this weekend. This includes lower runout zones in valley bottoms.
Details about Wednesday's avalanche fatality will be updated on our accidents page: https://alaskasnow.org/haines-hac/haines-accidents/
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