Bollettino valanghe

Logan

Utah Avalanche Center
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In sintesi

A CONSIDERABLE danger exists in drifted upper elevation terrain, where people are likely to trigger avalanches of wind-drifted snow failing up to 2 feet deep on a thin, persistent, weak layer. Avoid steep slopes where the snow gets saturated from the sun and warm temperatures. The best riding terrain today will be on sheltered slopes less than 30°.

Careful snowpack evaluation, cautious route-finding, and conservative decision-making are essential for safe backcountry travel.

Problemi valanghivi

  • Wind Slabs

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    Probabilità
    Likely
    Dimensione
    2

    Drifting by winds from the west in the last couple of days created stiff wind slabs in exposed upper-elevation terrain. Winds from the southwest will increase this afternoon and, in some areas, people are likely to trigger avalanches of wind-drifted snow up to 2-3 feet deep on drifted slopes steeper than 30°.

    • Watch for and avoid fresh wind slabs on the lee side of major ridges, corniced slopes, and in and around terrain features like cliff bands, sub-ridges, gully walls, and mid-slope rollovers.
    • Stay well away from and out from under overhanging cornices, which may break further back than expected.
    • Obvious signs of instability include cracking and collapsing, but these red flags may not be present when avalanches occur.
    • Soft slab and loose avalanches of new snow are possible even in more sheltered terrain, and natural avalanches are most likely during periods of particularly heavy snowfall.

  • Persistent Slabs

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    Probabilità
    Likely
    Dimensione
    2

    Avalanches around 2-3 feet deep may fail on a thin layer of small-grained, sugary, or faceted snow that was on the snow surface on Wednesday, 2/14. This thin, persistent weak layer was buried by the productive storms on Thursday, Friday and Sunday but should heal or gain strength pretty quickly. Reports of audible collapsing (whumpfs) and a couple of remotely triggered avalanches on Saturday confirm that this layer may still be unstable in some areas. The problem is more pronounced in sunny terrain where the thin layer of faceted snow sits atop a supportable melt-freeze crust.

  • Loose Wet

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    Probabilità
    Possible
    Dimensione
    1

    Wet snow avalanches might be possible this morning with warm temperatures and a bit of sunshine. Roller balls and pinwheels are signs of instability. If the snow you're on gets saturated, move to a cooler aspect and/or elevation.

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Recent Activity

Numerous 1 to 2-foot deep natural avalanches were observed at upper elevations across the zone Saturday morning on east through south-facing slopes. Saturday morning, a possibly remotely triggered slide was observed on Cornice Ridge on a SE facing slope at 9600' in elevation. The avalanche was estimated to be 18" deep and 150' wide. Riders reported remotely triggering a good-sized avalanche in Three Terraces Bowl in upper Providence Canyon on the east side of Providence Peak on a southeast-facing slope at around 9500' (~2' deep and 200' wide, running around 700vrt'), and the party also noted several recent naturals. No avalanches were reported yesterday. Check out local observations and avalanches HERE.

Snow and Weather

The Logan area mountains got another good shot of snow yesterday picking up 1.3" SWE at the Tony Grove Snotel. With strong winds yesterday and more again this afternoon, dangerous conditions still exist where wind-drifted snow has overloaded the old snow/new snow interface from 2/14. Riding conditions are very good on all aspects and elevations away from wind-affected areas and we have excellent coverage across the zone, Today, your best option is to stick to safe slopes less than 30°. Human-triggered slab avalanches up to 2-3 feet deep are likely on drifted upper-elevation slopes steeper than 30°.

The Tony Grove Snotel at 8400' reports 1.3" SWE (snow water equivalent) from yesterday, it's currently 22° F, and there is 99" of total snow. The wind is blowing from the southwest this morning at around 29 mph, with gusts around 35 mph at the 9700' CSI Logan Peak weather station. At 9500' on Paris Peak, winds from the southwest are blowing around 16 mph, and it's 20° F.

We'll have a short-lived break in the weather this morning before another system moves into the area this afternoon with strong winds and snowfall. Temperatures at 8500' will be around 34° F today, with winds blowing from the southwest at 17-22 mph and gusts as high as 33 mph. The National Weather Service has issued a Winter Weather Advisory for tonight through tomorrow night with the strongest winds this afternoon into tonight. The mountains will receive 6-12" of snow by tomorrow evening. We'll see continued snowfall through Thursday morning.

You know it's getting deep when the Tony Grove campground latrines are almost buried. Pic from 2/16.

Additional Info

This avalanche in Three Terraces (upper Providence Canyon) was remotely triggered Saturday morning by a rider on a snowmobile.

We found a layer of small-grained, sugary snow at the interface of Wednesday's snow surface and Thursday's new snow. The "Valentines persistent weak layer (PWL)"

General Announcements

-Listen to your very own Logan Zone avalanche forecasters on the UAC Podcast HERE.

-Read my recent blog about wind, drifting, and avalanches HERE.

-Sign up for forecast region-specific text message alerts. You will receive messages about changing avalanche conditions, watches, and warnings...HERE.

-For all questions on forecasts, education, Know Before You Go, events, online purchases, or fundraising, call 801-365-5522.

-To report an avalanche or submit an observation from the backcountry, go HERE.

-Come practice companion rescue at the Franklin Basin TH Beacon Training Park. It's free and open to everyone. For easy user instructions, go HERE.

-Paige will update this forecast by 7:30 AM tomorrow. This forecast is from the U.S.D.A. Forest Service, which is solely responsible for its content. This forecast describes general avalanche conditions, and local variations always occur.

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